Patent Application
20110210242
The present invention relates to an ion source, a mass spectrometer, an elemental analyser, a method of ionising a sample, a method of mass spectrometry and a method of elemental analysis of a sample.
A principal use of mass spectrometers is to determine the mass to charge ratio of ions generated from an unknown substance in order to provide information from which to aid the identification of the substance. Where the unknown substance comprises one or more organic compounds it is commonly necessary to determine the elemental composition of these compounds. This information is helpful, and often essential, for the identification of the organic compounds present in the unknown substance.
The measurement of the mass of an organic compound is rarely adequate information from which to determine the elemental composition of the compound. The element carbon may combine with any or all of the elements hydrogen, nitrogen, oxygen, sulphur, phosphorous, fluorine, chlorine and bromine (which are the most common constituents of organic compounds) in numerous different proportions so that it is likely that an organic compound with a given nominal molecular weight will have a large number of possible elemental compositions.
The different isotopes of the different elements do not have precise integer masses but instead have a small mass sufficiency or deficiency (of the order of +/− a few hundredths of a mass unit) with respect to its nominal or integer mass. Hence, the exact mass of an organic molecule is not an integer and is generally not precisely the same as those of other organic molecules with the same nominal or integer mass. Hence, if the measurement of the molecular weight is made to a higher accuracy it is possible to eliminate a large number of possible elemental compositions that have the same nominal or integer mass. Accurate mass determination reduces the number of possible elemental compositions, and the more accurate the mass determination the smaller the number of possible elemental compositions.
Inspection of the isotopic distribution of the molecular ion may also help to reduce the number of possible elemental compositions. For example, the presence of chlorine and/or bromine is usually easily recognised since these elements have very distinct isotope distributions. The isotope ratio for chlorine, Cl35/Cl37, is approximately 3, and the isotope ratio for bromine, Br79/Br81, is approximately 1, both of which are quite different to those of other commonly occurring elements in organic compounds. The element sulphur also has a relatively distinctive isotope ratio. The ratio S32/S34 is approximately 22.5 and with careful measurements of the isotope ratios of a molecular ion it is sometimes possible to determine if sulphur atoms are present in the molecule, and if so approximately how many. However, it is considerably more difficult to determine if sulphur is present or not if the molecules of interest also contain either or both of chlorine and bromine. Information regarding the likely number of chlorine and bromine atoms in the molecule, or in the absence of chlorine and bromine, the range within which the number of sulphur atoms are likely to be present in the molecule, will help reduce the number of possible elemental compositions for an unknown organic molecule analysed by mass spectrometry. Apart from the determination of the likely number of chlorine and/or bromine atoms in each molecule, or, in the absence of chlorine and bromine, the determination to a lower precision of the approximate number of sulphur atoms in each molecule, it is very difficult or impossible to determine anything very useful from the molecular ion isotope distribution about the presence and relative numbers of the other common elements occurring in organic compounds. In particular, fluorine and phosphorous are mono-isotopic and hydrogen, nitrogen and oxygen have very low abundance secondary isotopes, and their presence in an organic molecule is not revealed in its molecular ion distribution.
When necessary, it is common practice to resort to other techniques in order to determine the elemental composition of an unknown organic compound. For example, elemental analysers may be used to determine the presence of certain types of element in the molecule.
There are several known methods for elemental analysis. In the more common types of elemental analyser a sample to be analyzed is weighed into a disposable tin or aluminium capsule. The sample is injected into a high temperature furnace and combusted in pure oxygen under static conditions. At the end of the combustion period, a dynamic burst of oxygen is added to ensure total combustion of all inorganic and organic substances. If tin capsules are used for the sample container, an initial exothermic reaction occurs raising the temperature of combustion to over 1800° C.
The resulting combustion products pass through specialized reagents to produce from the elemental carbon, hydrogen, and nitrogen: carbon dioxide (CO2), water (H2O), nitrogen (N2) and N oxides. These reagents also remove all other interferences including halogens, sulphur and phosphorus. The gases are then passed over copper to scrub excess oxygen, and to reduce oxides of nitrogen to elemental nitrogen.
The resulting mixture of gases may then be separated, for example by gas chromatography and/or may be analysed, for example, using specific detectors. The gas mixture may be measured using a series of high-precision thermal conductivity detectors, each containing a pair of thermal conductivity cells. A water trap is provided between the first two cells. The differential signal between the cells is proportional to the water concentration which is a function of the amount of hydrogen in the original sample. A carbon dioxide trap is provided between the next two cells for measuring carbon. Finally, nitrogen is measured against a helium reference.
Sulphur is commonly measured separately, as sulphur dioxide, by replacing the combustion and reduction reagents. Oxygen is also commonly measured separately by pyrolysis in the presence of platinized carbon. The oxygen is finally measured as carbon dioxide.
Known elemental analysers are not particularly sensitive when compared with that commonly achieved by mass spectrometry. Typically 1-5 mg of sample is required, or more for samples with low carbon content. The analysis time is quite long, typically of the order of 5 minutes for carbon, hydrogen and nitrogen analysis. Hence, the technique is too slow to be used when directly coupled to gas or liquid chromatography. Hence the sample needs to be purified separately before analysis. Furthermore, if the sample is in solution, as would be the case for separation by liquid chromatography, it is necessary to isolate, collect and desolvate a sample before submission for elemental analysis.
More recently the technique of gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) has been developed wherein a mixture of organic materials are separated by gas chromatography, combusted to carbon dioxide, water and other oxides, and the 13C/12C isotope ratio is then measured by isotope ratio mass spectrometry. The effluent from a gas chromatography capillary column is arranged to first enter a motorised valve to allow solvent to be diverted to waste to prevent premature depletion of the combustion reactor. The analytes eluting from the capillary column are then directed to an alumina or quartz combustion tube loaded with an oxidising reagent such as copper oxide (CuO), nickel oxide (NiO) or zinc oxide (ZnO). A mixture of oxidising reagents may be used and a catalytic material may also be added. For example, the combustion tube may be loaded with a twisted strand of copper, platinum and nickel wires. The combustion tube is heated, typically to between 900° C. and 950° C., and is periodically recharged with oxygen to convert the surface layers of the copper wire to copper oxide and the nickel wire to nickel oxide. Following combustion, the effluent is dried in a Nafion® water trap or cryogenic water trap and the dried effluent is admitted to the isotope ratio mass spectrometer.
In comparison to elemental analysis isotope ratio mass spectrometry (EA-IRMS), the GCC-IRMS method requires lower levels of analyte i.e. nanomoles versus micromoles of carbon. It is also faster with the gas-phase combustion process occurring on a millisecond time scale. GCC-IRMS has proven to be adequate for fast GC detection thereby providing the convenience of on-line isolation of components. However, this method is not appropriate for the measurement of the isotope ratios of all the elements commonly occurring in organic compounds and for similar reasons it is not appropriate for the elemental analysis of organic compounds.
In summary, accurate mass measurement of an organic compound using mass spectrometry is, in itself, rarely adequate for determining the elemental composition of the organic compound. The determination of the elemental composition is aided by the information gained from separate measurements, such as the information gained from measurements with an elemental analyser. However, elemental analysers are relatively insensitive and are relatively slow. If the sample is a mixture of organic compounds, as the vast majority of samples are, then it is necessary to isolate the components of the mixture prior to the elemental analysis. The speed of the elemental analyser does not allow on-line interfacing to chromatography. Furthermore, liquid chromatography would require the additional process of removing solvent before submission of the effluent material to the elemental analyser. The methods employed in GCC-IRMS allow on-line interfacing to gas chromatography, and provide improved sensitivity, but are not suitable for elemental analysis. The methods employed in GCC-IRMS are also not appropriate to liquid chromatography since it is necessary to remove all solvent material before submission of the effluent material to the combustion chamber. Finally, there is no method for the elemental analysis of ionised organic molecules, or for the elemental analysis of fragment ions, daughter ions, or decomposition or reaction product ions of organic molecules.
It is desired to provided an improved apparatus and method for determining the elemental composition of an organic compound and/or for determining an isotope ratio of one or more elements present in an organic compound.
According to an aspect of the present invention there is provided an ion source comprising:
a source chamber; and
a first device located within the source chamber which is arranged and adapted to at least in part fully oxidise, fluorinate, chlorinate or halogenate a sample which is introduced, in use, into the source chamber.
The sample preferably comprises an organic sample.
According to the preferred embodiment sample molecules or sample ions are preferably combusted upon impacting the first device which is preferably heated. At least some of the elements in the sample molecules or sample ions are fully oxidised i.e. carbon is converted into carbon dioxide molecules and hydrogen is converted into water molecules.
According to another embodiment there is provided apparatus comprising a chamber and a first device located within the chamber wherein the first device is arranged and adapted to oxidise, fluorinate, chlorinate or halogenate sample molecules or sample ions which are caused to impact the first device and wherein the chamber and/or the first device are maintained at a pressure below atmospheric pressure and further preferably are maintained at a pressure ≦10−5 mbar. It will be apparent that the apparatus is maintained at a much lower pressure than conventional combustion sources which are typically maintained at atmospheric pressure. Furthermore, the apparatus preferably further comprises an electron beam within the chamber which preferably ionises the gaseous products resulting from the oxidisation, fluorination, chlorination or halogenation of the sample molecules or sample ions by the first device.
The ion source preferably further comprises a second device located within the source chamber which is arranged and adapted to at least in part fully oxidise, fluorinate, chlorinate or halogenate a sample which is introduced, in use, into the source chamber. The second device is preferably spaced apart from the first device or comprises a separate region or portion of the first device.
The phrase “at least in part fully oxidise, fluorinate, chlorinate or halogenate a sample” is intended to include some sample molecules or ions comprising carbon being full converted to carbon dioxide (rather than carbon monoxide).
According to the preferred embodiment the source chamber is preferably located in a vacuum chamber which is preferably maintained, in use, at a pressure selected from the group consisting of: (i) ≦10−5 mbar; (ii) ≦10−6 mbar; (iii) ≦10−7 mbar; (iv) ≦10−8 mbar; and (v) ≦10−9 mbar.
At least one surface of the first device and/or the second device preferably comprises one or more oxidising reagents for oxidising the sample. The one or more oxidising reagents are preferably selected from the group consisting of: (i) antimony oxide (Sb2O3); (ii) arsenic oxide (As2O5); (iii) cobalt oxide (Co3O4); (iv) copper oxide (CuO); (v) iridium oxide (IrO2); (vi) iron oxide (Fe3O4); (vii) lead oxide (Pb3O4); (viii) lead oxide (PbO2); (ix) palladium oxide (PdO); (x) potassium oxide (K2O); (xi) rhodium oxide (Rh2O3); (xii) silver oxide (Ag2O); (xiii) sodium peroxide (Na2O2); (xiv) tellurium oxide (TeO2); (xv) tin oxide (SnO); (xvi) chromium oxide (CrO2); (xvii) chromium oxide (Cr2O5); (xviii) germanium oxide (GeO); (xix) iridium oxide (Ir2O3); (xx) lead oxide (Pb2O3); (xxi) manganese oxide (Mn2O3); (xxii) manganese oxide (MnO2); (xxiii) molybdenum oxide (MoO2); (xxiv) nickel oxide (Ni2O3); (xxv) platinum oxide (PtO); (xxvi) rhenium oxide (ReO2); (xxvii) rhenium oxide (ReO3); (xxviii) rubidium oxide (Rb2O); (xxix) ruthenium oxide (RuO2); (xxx) tungsten oxide (WO2); and (xxxi) zinc oxide (ZnO).
According to the preferred embodiment at least one surface of the first device and/or the second device comprises one or more fluorinating reagents for fluorinating the sample. The one or more fluorinating reagents are preferably selected from the group consisting of: (i) copper fluoride (CuF2); (ii) iridium fluoride (IrF3); (iii) manganese fluoride (MnF3); (iv) niobium fluoride (NbF4); (v) ruthenium fluoride (RuF3); (vi) thallium fluoride (TIF3); (vii) titanium fluoride (TiF3); (viii) tungsten fluoride (WF3); (ix) vanadium fluoride (VF4); and (x) nickel fluoride (NiF6, NiF4, NiF3).
According to the preferred embodiment at least one surface of the first device and/or the second device comprises one or more chlorinating reagents for chlorinating the sample.
According to the preferred embodiment at least one surface of the first device and/or the second device comprises one or more halogenating reagents for halogenating the sample.
According to the preferred embodiment at least one surface of the first device and/or the second device comprises a catalytic material. The catalytic material preferably comprises one or more elements selected from the group consisting of: (i) nickel; (ii) platinum; (iii) palladium; (iv) rhodium; and (v) a transition element.
According to the preferred embodiment at least one surface of the first device and/or the second device is porous or sintered.
According to the preferred embodiment the first device comprises a heating element for heating a surface of the first device to a temperature selected from the group consisting of: (i) ≧150°; (ii) ≧200°; (iii) ≧250°; (iv) ≧300°; (v) ≧350°; (vi) ≧400°; (vii) ≧450°; (viii) ≧500°; (ix) ≧550°; (x) ≧600°; (xi) ≧650°; (xii) ≧700°; (xiii) ≧750°; (xiv) ≧800°; (xv) ≧850°; (xvi) ≧900°; (xvii) ≧950°; and (xviii) ≧1000°.
According to the preferred embodiment the second device comprises a heating element for heating a surface of the second device to a temperature selected from the group consisting of: (i) ≧150°; (ii) ≧200°; (iii) ≧250°; (iv) ≧300°; (v) ≧350°; (vi) ≧400°; (vii) ≧450°; (viii) ≧500°; (ix) ≧550°; (x) ≧600°; (xi) ≧650°; (xii) ≧700°; (xiii) ≧750°; (xiv) ≧800°; (xv) ≧850°; (xvi) ≧900°; (xvii) ≧950°; and (xviii) ≧1000°.
The ion source preferably further comprises a device for generating an electron beam, wherein the electron beam is arranged to ionise at least some gaseous products resulting from sample molecules or sample ions impacting the first device and/or the second device and becoming oxidised and/or fluorinated and/or chlorinated and/or halogenated.
The ion source preferably further comprises a first capillary or introduction tube through which:
(i) a sample in a liquid or gaseous state is introduced, in use, into the source chamber; and/or
(ii) a purging gas is introduced in a mode of operation prior to, with or subsequent to the introduction of the sample into the source chamber; and/or
(iii) oxygen and/or fluorine and/or chlorine and/or a halogen is introduced in a mode of operation in order to recharge a surface of the first device and/or the second device.
The ion source preferably further comprises a second capillary or introduction tube through which:
(i) a sample in a liquid or gaseous state is introduced, in use, into the source chamber; and/or
(ii) a purging gas is introduced in a mode of operation prior to, with or subsequent to the introduction of the sample into the source chamber; and/or
(iii) oxygen and/or fluorine and/or chlorine and/or a halogen is introduced in a mode of operation in order to recharge a surface of the first device and/or the second device.
According to a less preferred embodiment the ion source may further comprise a vacuum insertion probe for introducing a solid into the source chamber. The vacuum insertion probe is preferably heated in use.
According to the preferred embodiment the ion source further comprises a first ion inlet through which sample ions are introduced into the ion source. Sample ions are preferably introduced into the ion source via the first ion inlet and are directed onto the first device and/or the second device and wherein the first device and/or the second device is arranged and adapted to oxidise, fluorinate, chlorinate or halogenate the sample ions.
In a first mode of operation sample ions may be arranged to enter the source chamber and wherein at least some or, at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the sample ions are directed on to the first device and/or the second device and wherein in a second mode of operation sample ions may be arranged to enter the source chamber and wherein at least some or at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the sample ions are arranged to be transmitted through the source chamber without being directed on to the first device and/or the second device.
The ion source preferably further comprises one or more electrodes for directing sample ions onto the first device and/or the second device.
According to the preferred embodiment in a mode of operation sample ions are directed onto the first device and/or the second device, preferably by the one of more electrodes, at an incident angle (preferably measured relative to the surface of the first device and/or the second device) of: (i) <15°; (ii) 15-30°; (iii) 30-45°; (iv) 45-60°; (v) 60-75°; and (vi) >75°.
According to the preferred embodiment in a mode of operation sample ions are directed onto the first device and/or the second device, preferably by the one of more electrodes, with an ion energy selected from the group consisting of: (i) <1 eV; (ii) <3 eV; (iii) <10 eV; (iv) <30 eV; (v) <100 eV; (vi) <300 eV; (vii) <1000 eV; (viii) >1 eV; (ix) >3 eV; (x) >10 eV; (xi) >30 eV; (xii) >100 eV; (xiii) >300 eV; and (xiv) >1000 eV.
The sample ions may comprise fragment, daughter or product ions of a sample material.
According to another aspect of the present invention there is provided a mass spectrometer or an elemental analyser comprising an ion source as described above.
According to another aspect of the present invention there is provided a method of ionising a sample comprising:
providing a source chamber;
introducing a sample into the source chamber; and
using a first device located within the source chamber to at least in part fully oxidise, fluorinate, chlorinate or halogenate the sample.
According to another aspect of the present invention there is provided a method of mass spectrometry comprising a method as described above.
According to an aspect of the present invention there is provided a method of analysing a sample comprising:
introducing a sample into an ion source;
at least in part fully oxidising, fluorinating, chlorinating or halogenating the sample using a first device to produce gaseous oxidised, fluorinated, chlorinated or halogenated products; and
ionising at least some of the gaseous oxidised, fluorinated, chlorinated or halogenated products to form a plurality of analyte ions.
The method preferably further comprises mass analysing the analyte ions.
The sample preferably comprises an organic sample.
According to an embodiment the method further comprises determining an isotope ratio of one or more elements present in the sample from the mass analysis of the analyte ions. The elements are preferably selected from the group consisting of: (i) carbon; (ii) hydrogen; (iii) nitrogen; (iv) oxygen; and (v) sulphur. Other embodiments are contemplated wherein the element may comprise chlorine or bromine.
According to an embodiment the isotope ratio comprises the ratio of two or more isotopes selected from the group consisting: (i) C12; (ii) C13; and (iii) C14.
According to an embodiment:
(i) the first device is arranged and adapted to at least in part fully oxidise the sample; and/or
(ii) the gaseous oxidised products include carbon dioxide (CO2); and/or
(iii) the isotope ratio comprises the ratio C14/C12; and/or
(iv) the isotope ratio is determined by analysing the intensity of C14O162 having a nominal mass to charge ratio of 46 to the intensity of C12O162 having a nominal mass to charge ratio of 44.
Other less preferred embodiments are contemplated wherein other ratios may be determined such as the ratio of C14/C13 and/or C13/C12 and/or C14/C13/C12.
According to the preferred embodiment both naturally occurring isotopes and isotopes such as C14 which may have been artificially introduced into a sample may be measured. C14 isotopes may, for example, have been introduced into a sample as part of a chemical or metabolic study of the sample.
According to an embodiment:
(i) the first device is arranged and adapted to at least in part fully fluorinate the sample; and/or
(ii) the gaseous oxidised products include carbon tetrafluoride (CF4); and/or
(iii) the isotope ratio comprises the ratio C14/C12; and/or
(iv) the isotope ratio is determined by analysing the intensity of C14F164 having a nominal mass to charge ratio of 90 to the intensity of C12F164 having a nominal mass to charge ratio of 88.
Other less preferred embodiments are contemplated wherein other ratios may be determined such as the ratio of C14/C13 and/or C13/C12 and/or C14/C13/C12.
According to an embodiment:
(i) the first device is arranged and adapted to at least in part fully iodinate the sample; and/or
(ii) the gaseous oxidised products include carbon tetraiodide (Cl4); and/or
(iii) the isotope ratio comprises the ratio C14/C12; and/or
(iv) the isotope ratio is determined by analysing the intensity of C14I1274 having a nominal mass to charge ratio of 522 to the intensity of C12I1274 having a nominal mass to charge ratio of 520.
Other less preferred embodiments are contemplated wherein other ratios may be determined such as the ratio of C14/C13 and/or C13/C12 and/or C14/C13/C12.
The method preferably further comprises measuring ion currents for ions of each mass to charge ratio of interest.
The method preferably further comprises processing the measured ion currents for ions of each mass to charge ratio of interest by:
(a) subtracting a background spectrum or ion current; and/or
(b) correcting measured ion currents for variations in response for ions of different mass to charge values.
According to another embodiment of the present invention the method further comprises a method of elemental analysis of the sample.
The method preferably further comprises measuring, determining or estimating the relative abundances of some or all of different elements present in an organic molecule or ions derived from an organic molecule.
According to an embodiment the method further comprises utilising the measurement, determination or estimation of the relative abundances of some or all of different elements present in the organic molecule to provide limits to, or to filter, the results of an elemental composition calculation derived from the measured mass or the accurate mass of an organic molecule or of an ion derived from an organic molecule.
The elements are preferably selected from the group consisting of: (i) carbon; (ii) hydrogen; (iii) nitrogen; (iv) oxygen; (v) sulphur; (vi) phosphorus; (vii) fluorine; (viii) chlorine; and (ix) bromine.
According to an aspect of the present invention there is provided apparatus for analysing a sample comprising:
an ion source into which a sample is introduced in use;
a first device for at least in part fully oxidising, fluorinating, chlorinating or halogenating the sample to produce gaseous oxidised, fluorinated, chlorinated or halogenated products; and
a device for ionising at least some of the gaseous oxidised, fluorinated, chlorinated or halogenated products to form a plurality of analyte ions.
The apparatus preferably further comprises a mass analyser for mass analysing the analyte ions.
According to an aspect of the present invention there is provided an isotope ratio mass spectrometer comprising apparatus as described above.
According to an aspect of the present invention there is provided an elemental analyser comprising apparatus as described above.
According to an aspect of the present invention there is provided a computer program executable by the control system of a mass spectrometer comprising an ion source comprising a source chamber and a first device located within the source chamber, the computer program being arranged to cause the control system:
to cause a sample which is introduced into the source chamber to be at least in part fully oxidised, fluorinated, chlorinated or halogenated by the first device.
According to an aspect of the present invention there is provided a computer program executable by the control system of a mass spectrometer, the computer program being arranged to cause the control system:
(i) to cause a sample to be at least in part fully oxidised, fluorinated, chlorinated or halogenated by a first device to produce gaseous oxidised, fluorinated, chlorinated or halogenated products;
(ii) to cause a device to ionise at least some of the gaseous oxidised, fluorinated, chlorinated or halogenated products to form a plurality of analyte ions; and
(iii) to cause a mass analyser to mass analyse the analyte ions.
According to an aspect of the present invention there is provided a computer readable medium comprising computer executable instructions stored on the computer readable medium, the instructions being arranged to be executable by a control system of a mass spectrometer comprising an ion source comprising a source chamber and a first device located within the source chamber, the computer program being arranged to cause the control system:
to cause a sample which is introduced into the source chamber to be at least in part fully oxidised, fluorinated, chlorinated or halogenated by the first device.
According to an aspect of the present invention there is provided a computer readable medium comprising computer executable instructions stored on the computer readable medium, the instructions being arranged to be executable by a control system of a mass spectrometer, the computer program being arranged to cause the control system:
(i) to cause a sample to be at least in part fully oxidised, fluorinated, chlorinated or halogenated by a first device to produce gaseous oxidised, fluorinated, chlorinated or halogenated products;
(ii) to cause a device to ionise at least some of the gaseous oxidised, fluorinated, chlorinated or halogenated products to form a plurality of analyte ions; and
(iii) to cause a mass analyser to mass analyse the analyte ions.
The computer readable medium is preferably selected from the group consisting of:
(i) a ROM; (ii) an EAROM; (iii) an EPROM; (iv) an EEPROM; (v) a flash memory; (vi) an optical disk; (vii) a RAM; and (viii) a hard disk drive.
According to another aspect of the present invention there is provided an apparatus comprising:
a source chamber;
a first ion inlet through which sample ions are introduced, in use, into the source chamber;
a first device located within the source chamber which is arranged and adapted to at least in part fully oxidise, fluorinate, chlorinate or halogenate the sample ions, wherein the source chamber is located in a vacuum chamber which is maintained, in use, at a pressure selected from the group consisting of: (i) ≦10−5 mbar; (ii) ≦10−6 mbar; (iii) ≦10−7 mbar; (iv) ≦10−8 mbar; and (v) ≦10−9 mbar; and
a device for generating an electron beam, wherein the electron beam is arranged to ionise at least some gaseous products resulting from the sample ions impacting the first device and becoming oxidised and/or fluorinated and/or chlorinated and/or halogenated.
According to another aspect of the present invention there is provided a method comprising:
providing a source chamber;
introducing sample ions into the source chamber;
using a first device located within the source chamber to at least in part fully oxidise, fluorinate, chlorinate or halogenate the sample ions, wherein the source chamber is located in a vacuum chamber which is maintained at a pressure selected from the group consisting of: (i) ≦10−5 mbar; (ii) ≦10−6 mbar; (iii) ≦10−7 mbar; (iv) ≦10−8 mbar; and (v) ≦10−9 mbar; and
generating an electron beam, wherein the electron beam is arranged to ionise at least some gaseous products resulting from the sample ions impacting the first device and becoming oxidised and/or fluorinated and/or chlorinated and/or halogenated.
A method of chemical analysis is preferably provided wherein the organic molecules of an organic substance, or ions derived from the organic molecules, are reacted with a chemical reagent within the vacuum system of a mass spectrometer to yield a plurality of small molecules (e.g. carbon dioxide) comprised of one or more constituent atoms of the organic molecules or ions derived from the organic molecules, and one or more atoms of the chemical reagent. For example, a substantial proportion of the organic molecules are fully oxidised thereby yielding a plurality of relatively small gaseous molecules such as carbon dioxide from oxidation of the carbon atoms from which the organic molecules were comprised. The plurality of small molecules are then preferably analysed by the mass spectrometer.
In a preferred embodiment, the small molecules that result from the reaction of the chemical reagent with the organic molecules or ions derived from the organic molecules, and which comprise more than one constituent atom of the organic molecule or ions derived from the organic molecules, are comprised of constituent atoms of the same element (e.g. water molecules from the oxidation of the hydrogen atoms from which the organic molecules were comprised).
In a preferred embodiment, the analysis of the small molecules by the mass spectrometer provides information which may be used to determine some or all of the different elements present in the organic molecules or ions derived from the organic molecules, and furthermore, an estimation of the relative abundance of the elements in the organic molecules or ions derived from the organic molecules.
The chemical reagent preferably comprises an oxidising reagent and the atoms of the chemical reagent preferably comprise oxygen atoms.
The oxidising chemical reagent preferably comprises one or more of: (i) antimony oxide (Sb2O3); (ii) arsenic oxide (As2O5); (iii) cobalt oxide (Co3O4); (iv) copper oxide (CuO); (v) iridium oxide (IrO2); (vi) iron oxide (Fe3O4); (vii) lead oxide (Pb3O4); (viii) lead oxide (PbO2); (ix) palladium oxide (PdO); (x) potassium oxide (K2O); (xi) rhodium oxide (Rh2O3); (xii) silver oxide (Ag2O); (xiii) sodium peroxide (Na2O2); (xiv) tellurium oxide (TeO2); (xv) tin oxide (SnO); (xvi) chromium oxide (CrO2); (xvii) chromium oxide (Cr2O5); (xviii) germanium oxide (GeO); (xix) iridium oxide (Ir2O3); (xx) lead oxide (Pb2O3); (xxi) manganese oxide (Mn2O3); (xxii) manganese oxide (MnO2); (xxiii) molybdenum oxide (MoO2); (xxiv) nickel oxide (Ni2O3); (xxv) platinum oxide (PtO); (xxvi) rhenium oxide (ReO2); (xxvii) rhenium oxide (ReO3); (xxviii) rubidium oxide (Rb2O); (xxix) ruthenium oxide (RuO2); (xxx) tungsten oxide (WO2); and (xxxi) zinc oxide (ZnO).
The chemical reagent may comprise a halogenating reagent and the atoms of the chemical reagent may comprise halogen atoms.
The chemical reagent may comprise a fluorinating reagent and the atoms of the chemical reagent may comprise fluorine atoms.
The fluorinating chemical reagent is preferably one or more of: (i) copper fluoride (CuF2); (ii) iridium fluoride (IrF3); (iii) manganese fluoride (MnF3); (iv) niobium fluoride (NbF4); (v) ruthenium fluoride (RuF3); (vi) thallium fluoride (TIF3); (vii) titanium fluoride (TiF3); (viii) tungsten fluoride (WF3); (ix) vanadium fluoride (VF4); and (x) nickel fluoride (NiF6, NiF4, NiF3).
The chemical reagent may comprise chlorinating reagent and the atoms of the chemical reagent may comprise chlorine atoms.
According to an embodiment of the present invention the chemical reagent is in the form of, or is present on, a surface. The chemical reagent preferably decomposes when heated. The chemical reagent preferably thermally decomposes at a temperature below which it melts or sublimes in vacuum. The surface is preferably rough or porous or sintered The surface is preferably heated. The surface is preferably heated to a temperature greater than: (i) 200° C.; (ii) 250° C.; (iii) 300° C.; (iv) 350° C.; (v) 400° C.; (vi) 450° C.; (vii) 500° C.; (viii) 550° C.; (ix) 600° C.; (x) 650° C.; (xi) 700° C.; (xii) 750° C.; (xiii) 800° C.; (xiv) 850° C.; (xv) 900° C.; (xvi) 950° C.; and (xvii) 1000° C.
In an embodiment of the present invention the chemical reagent forms, or is deposited on, the surface of a dispenser cathode.
In another embodiment of the present invention the surface includes a catalytic material. The catalytic material preferably includes one or more of: (i) nickel; (ii) platinum; (iii) palladium; (iv) rhodium; and (v) a transition element.
In a preferred embodiment of the present invention the small molecules are further ionised prior to analysis by mass spectrometry. The small molecules may be ionised by Electron impact (EI) ionisation and/or by Thermal Ionisation (TI)
In a preferred embodiment of the present invention the heated chemically reactive surface, and subsequent means for ionisation, are maintained at high vacuum. The pressure in the high vacuum is preferably less than (i) 10−6 mbar; (ii) 10−7 mbar; (iii) 10−8 mbar; and (iv) 10−9 mbar.
In an alternative embodiment of the present invention the heated chemically reactive surface, and subsequent means for ionisation, are preferably continuously purged by a flow of an inert or un-reactive gas. The inert or un-reactive gas is preferably one or more of: (i) helium; (ii) neon; (iii) argon; and (iv) a noble gas. The pressure of the inert or un-reactive gas is preferably less than: (i) 10−2 mbar; (ii) 10−3 mbar; (iii) 10−4 mbar; and (iv) 10−5 mbar.
In a preferred embodiment of the present invention the ions formed from the small molecules are mass analysed by a mass spectrometer. The mass spectrometer is preferably (i) a quadrupole mass filter; (ii) a 3D or Paul ion trap; (iii) a linear quadrupole ion trap; (iv) a Time of Flight mass spectrometer; (v) an orthogonal acceleration time of Flight mass spectrometer; (vi) a magnetic sector; (vii) an electrostatic ion trap mass analyser utilising Fourier Transform (FT); (viii) a magnetic ion trap utilising Fourier Transform (FT); (ix) an Orbitrap®; and (x) a Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometer.
The mass spectrometer preferably comprises a magnetic sector incorporating multiple detectors to allow simultaneous detection of ions of more than one mass to charge ratio value.
In a preferred embodiment of the present invention the measured ion currents for ions of each mass to charge ratio value of interest acquired by the mass spectrometer are processed such as to perform any or all of the following functions: (a) subtraction of background spectrum or ion current; (b) correction of measured ion currents for variations in response for ions of different mass to charge values; where variations in response for ions of different mass to charge ratio values are the products of variations in any or all of (i) variations in ionisation efficiency, (ii) variations in ion transmission efficiency, (iii) variations in relative ion sampling times or ion transmission and detection duty cycles, (iv) variations in ion detection efficiencies; (c) measurement of the relative abundances of ions of the small molecules comprising different elements present in the organic molecule or ions derived from the organic molecule; (d) determinations or estimations of the relative abundances of some or all of the different elements present in the organic molecules or ions derived from the organic molecules; and (e) utilisation of determinations or estimations of relative abundances of some or all of the different elements present in the organic molecules to provide limits to, or to filter, the results of an elemental composition calculation derived from the measured mass, or preferably the accurate mass, of an organic molecule, or of an ion derived from the organic molecule
In another embodiment of the present invention the measured ion currents for ions of each mass to charge ratio value of interest acquired by the mass spectrometer are processed such as to perform any or all of the following functions: (a) subtraction of background spectrum or current; (b) correction of measured currents for variations in response for ions of different mass to charge ratio values; where variations in response for ions of different mass to charge ratio values are the products of variations in any or all of: (i) variations in ionisation efficiency; (ii) variations in ion transmission efficiency; (iii) variations in ion sampling times or ion transmission and detection duty cycles; and (iv) variations in ion detection efficiencies; and (c) measurement of the relative isotope abundance ratios for one or more of the elements present in the organic molecules or ions derived from the organic molecules.
In a preferred embodiment of the present invention the organic molecules are preferably introduced directly into the vacuum system of the mass spectrometer. The organic molecules are preferably introduced through a capillary tube or through one or more apertures into the vacuum system of the mass spectrometer. The stream of organic molecules preferably form a molecular beam that is directed at the heated chemically reactive surface.
In another preferred embodiment of the present invention the organic molecules are ionised before being exposed to the heated chemically reactive surface. The ions are preferably directed at the surface of the heated chemically reactive surface. The ions preferably impact the heated chemically reactive surface at an incident angle (measured relative to the plane of the reactive surface) of: (i) less than 15°; (ii) between 15° and 30°; (iii) between 30° and 45°; (iv) between 45° and 60°; (v) between 60° and 75°; and (vi) greater than 75°. The energy of the ions is preferably: (i) less than 1 eV; (ii) less than 3 eV; (iii) less than 10 eV; (iv) less than 30 eV; (v) less than 100 eV; (vi) less than 300 eV; (vii) less than 1000 eV; (viii) greater than 1 eV; (ix) greater than 3 eV; (x) greater than 10 eV; (xi) greater than 30 eV; (xii) greater than 100 eV; (xiii) greater than 300 eV; and (xiv) greater than 1000 eV.
In another preferred embodiment of the present invention the organic molecules are preferably ionised before being exposed to the heated chemically reactive surface by: (i) Electron Impact (EI) ionisation; (ii) Chemical Ionisation (CI); (iii) Field Ionisation (FI); (iv) Field Desorption (FD) Ionisation; (v) Fast Atom Bombardment (FAB); (vi) Liquid SIMS; (vii) Atmospheric Pressure Ionisation (API); (viii) Electrospray Ionisation (ESI); (ix) Atmospheric Pressure Chemical Ionisation (APCI); (x) Atmospheric Pressure Photo-Ionisation (APPI); (xi) Laser Desorption Ionisation; (xii) Matrix Assisted Laser Desorption Ionisation (MALDI); and (xiii) Desorption Electrospray Ionisation (DESI).
In another embodiment of the present invention the ions derived from the organic molecules are, prior to exposure to the heated chemically reactive surface: (a) selected according to their mass to charge ratio values, where ion selection according to mass to charge ratio value utilises: (i) a quadrupole mass filter; (ii) a Wien filter; (iii) a magnetic sector; (iv) a linear or 3D ion trap; (v) a Time-of-Flight mass spectrometer; (b) selected according to their ion mobility, where ion selection according to ion mobility utilises: (i) a drift tube; (ii) a travelling wave; or (c) selected according to their differential ion mobility, where ion selection according to their differential ion mobility utilises: (i) a Differential Mobility Spectrometer (DMS); (ii) a Field Asymmetric Ion Mobility Spectrometer (FAIMS).
In another embodiment of the present invention the ions derived from the organic molecules are, prior to exposure to the heated chemically reactive surface, partially fragmented or decomposed, or reacted. The ions are preferably partially fragmented or decomposed or reacted by: (i) collision with gas molecules or atoms; (ii) collisions with an inert or un-reactive surface; (iii) collisions with electrons; (iv) Electron Capture Dissociation (ECD); (v) collisions with ions; (vi) Electron Transfer Dissociation (ETD); (v) collisions with metastable atoms; (vi) collisions with metastable molecules; and (vii) collisions with metastable ions.
In another embodiment of the present invention the organic molecules are first separated or purified by gas chromatography, liquid chromatography or capillary electrophoresis.
According to an embodiment of the present invention a mass spectrometer is provided wherein the mass spectrometer further comprises an ion source selected from the group consisting of: (i) an Electrospray ionisation (“ESI”) ion source; (ii) an Atmospheric Pressure Photo Ionisation (“APPI”) ion source; (iii) an Atmospheric Pressure Chemical Ionisation (“APCI”) ion source; (iv) a Matrix Assisted Laser Desorption Ionisation (“MALDI”) ion source; (v) a Laser Desorption Ionisation (“LDI”) ion source; (vi) an Atmospheric Pressure Ionisation (“API”) ion source; (vii) a Desorption Ionisation on Silicon (“DIOS”) ion source; (viii) an Electron Impact (“EI”) ion source; (ix) a Chemical Ionisation (“CI”) ion source; (x) a Field Ionisation (“FI”) ion source; (xi) a Field Desorption (“FD”) ion source; (xii) an Inductively Coupled Plasma (“ICP”) ion source; (xiii) a Fast Atom Bombardment (“FAB”) ion source; (xiv) a Liquid Secondary Ion Mass Spectrometry (“LSIMS”) ion source; (xv) a Desorption Electrospray Ionisation (“DESI”) ion source; (xvi) a Nickel-63 radioactive ion source; (xvii) an Atmospheric Pressure Matrix Assisted Laser Desorption Ionisation ion source; (xviii) a Thermospray ion source; (xix) an Atmospheric Sampling Glow Discharge Ionisation (“ASGDI”) ion source; and (xx) a Glow Discharge (“GD”) ion source.
The mass spectrometer preferably further comprises one or more continuous or pulsed ion sources.
The mass spectrometer preferably further comprises one or more ion guides.
The mass spectrometer preferably further comprises one or more ion mobility separation devices and/or one or more Field Asymmetric Ion Mobility Spectrometer devices.
The mass spectrometer preferably further comprises one or more ion traps or one or more ion trapping regions.
The mass spectrometer preferably further comprises one or more collision, fragmentation or reaction cells selected from the group consisting of: (i) a Collisional Induced Dissociation (“CID”) fragmentation device; (ii) a Surface Induced Dissociation (“SID”) fragmentation device; (iii) an Electron Transfer Dissociation (“ETD”) fragmentation device; (iv) an Electron Capture Dissociation (“ECD”) fragmentation device; (v) an Electron Collision or Impact Dissociation fragmentation device; (vi) a Photo Induced Dissociation (“PID”) fragmentation device; (vii) a Laser Induced Dissociation fragmentation device; (viii) an infrared radiation induced dissociation device; (ix) an ultraviolet radiation induced dissociation device; (x) a nozzle-skimmer interface fragmentation device; (xi) an in-source fragmentation device; (xii) an in-source Collision Induced Dissociation fragmentation device; (xiii) a thermal or temperature source fragmentation device; (xiv) an electric field induced fragmentation device; (xv) a magnetic field induced fragmentation device; (xvi) an enzyme digestion or enzyme degradation fragmentation device; (xvii) an ion-ion reaction fragmentation device; (xviii) an ion-molecule reaction fragmentation device; (xix) an ion-atom reaction fragmentation device; (xx) an ion-metastable ion reaction fragmentation device; (xxi) an ion-metastable molecule reaction fragmentation device; (xxii) an ion-metastable atom reaction fragmentation device; (xxiii) an ion-ion reaction device for reacting ions to form adduct or product ions; (xxiv) an ion-molecule reaction device for reacting ions to form adduct or product ions; (xxv) an ion-atom reaction device for reacting ions to form adduct or product ions; (xxvi) an ion-metastable ion reaction device for reacting ions to form adduct or product ions; (xxvii) an ion-metastable molecule reaction device for reacting ions to form adduct or product ions; (xxviii) an ion-metastable atom reaction device for reacting ions to form adduct or product ions; and (xxix) an Electron Ionisation Dissociation (“EID”) fragmentation device.
The mass spectrometer preferably further comprises a mass analyser selected from the group consisting of: (i) a quadrupole, mass analyser; (ii) a 2D or linear quadrupole mass analyser; (iii) a Paul or 3D quadrupole mass analyser; (iv) a Penning trap mass analyser; (v) an ion trap mass analyser; (vi) a magnetic sector mass analyser; (vii) a double focusing magnetic sector mass analyser; (viii) Ion Cyclotron Resonance (“ICR”) mass analyser; (ix) a Fourier Transform Ion Cyclotron Resonance (“FTICR”) mass analyser; (x) an electrostatic or orbitrap mass analyser; (xi) a Fourier Transform electrostatic or orbitrap mass analyser; (xii) a Fourier Transform mass analyser; (xiii) a Time of Flight mass analyser; (xiv) an orthogonal acceleration Time of Flight mass analyser; and (xv) a linear acceleration Time of Flight mass analyser.
The mass spectrometer preferably further comprises one or more energy analysers or electrostatic energy analysers.
The mass spectrometer preferably further comprises one or more ion detectors.
The mass spectrometer preferably further comprises one or more mass filters selected from the group consisting of: (i) a quadrupole mass filter; (ii) a 2D or linear quadrupole ion trap; (iii) a Paul or 3D quadrupole ion trap; (iv) a Penning ion trap; (v) an ion trap; (vi) a magnetic sector mass filter; (vii) a Time of Flight mass filter; and (viii) a Wein filter.
The mass spectrometer preferably further comprises a device or ion gate for pulsing ions.
The mass spectrometer preferably further comprises a device for converting a substantially continuous ion beam into a pulsed ion beam.
According to an embodiment the mass spectrometer further comprises a C-trap and an orbitrap® mass analyser comprising an outer barrel-like electrode and a coaxial inner spindle-like electrode, wherein in a first mode of operation ions are transmitted to the C-trap and are then injected into the orbitrap® mass analyser and wherein in a second mode of operation ions are transmitted to the C-trap and then to a collision cell or Electron Transfer Dissociation device wherein at least some ions are fragmented into fragment ions, and wherein the fragment ions are then transmitted to the C-trap before being injected into the orbitrap® mass analyser.
According to an embodiment the mass spectrometer further comprises a stacked ring ion guide comprising a plurality of electrodes each having an aperture through which ions are transmitted in use and wherein the spacing of the electrodes increases along the length of the ion path, and wherein the apertures in the electrodes in an upstream section of the ion guide have a first diameter and wherein the apertures in the electrodes in a downstream section of the ion guide have a second diameter which is smaller than the first diameter, and wherein opposite phases of an AC or RF voltage are applied, in use, to successive electrodes.
Various embodiments of the present invention will now be described, by way of example, and with reference to the accompanying drawings in which:
An embodiment of the present invention will now be described.
For the elements considered in
Some types of mass spectrometer are capable of measuring the mass of an ion with an accuracy of about +/−1 ppm (+/−one standard deviation or 68% confidence). Under situations where enough sample and enough time is available to achieve a mass accuracy of about +/−1 ppm (68% confidence) then a mass search window of +/−4 ppm or +/−0.001 Da may be set. In this case, the number of possible elemental compositions is reduced to 108. However, 108 possible elemental compositions is still a long way short of the target of just one possible elemental composition.
The elements chlorine and bromine have noticeably different isotope ratios to those of the other elements that have been considered. The isotope ratio for chlorine Cl35/Cl37 is approximately 3 and the isotope ratio for bromine Br79/Br81 is approximately 1. Hence, it is often possible to recognise if atoms of chlorine and/or bromine are present in the molecule. If atoms of chlorine and/or bromine are present then the number of such atoms per molecule may be determined from a measurement of the isotope ratios for the molecular ion. Column B in
The element sulphur also has a relatively distinctive isotope ratio, although far less distinctive than that of chlorine and bromine. The ratio S32/S34 is approximately 22.5 and with careful measurements of the isotope ratios of a molecular ion it is possible to determine if sulphur atoms are present in the molecule and if so approximately how many. Column C in
In this situation, where the mass has been accurately measured and the search window has been set to +/−4 ppm or +/−0.001 Da, the number of possible elemental compositions is reduced to 30. This is considerably less than the 108 possible elemental compositions first calculated but is still short of the target of just one possible elemental composition.
The table shown in
For the elements considered in
Column B in
Column C in
In this situation, where the mass has been accurately measured and the search window has been set to +/−4 ppm or +/−0.002 Da, the number of possible elemental compositions is reduced to 989. This is considerably less than the 3662 possible elemental compositions first calculated but is still a long way short of the target of just one possible elemental composition.
The tables shown in
The table in
It has been assumed above that it has not been possible to narrow the range of the number of oxygen atoms in the molecule since it has been assumed that the molecule has been fully oxidised or combusted in order to determine the relative amounts of the other elements in the molecule. However, if required, the molecule may alternatively be fully fluorinated in order to determine the relative number of oxygen atoms in the molecule. In column D in
The table in
The data tabulated in column E of
These examples illustrate that the elemental composition of an organic molecule can be uniquely determined by a combination of accurate mass measurement of the molecule, a measurement to determine what elements are present in the molecule and a measurement of the approximately relative numbers of the atoms of the different elements present in the molecule. As the mass of the molecule increases, the required accuracy of measurement of the mass of the molecule and the required accuracy of determination of the approximately relative numbers of atoms of the different elements present increases in order to uniquely determine the elemental composition of the molecule.
A preferred embodiment of the present invention will now be described with reference to
A sample is preferably introduced into the source chamber 1 via the sample introduction, capillary tube 2 which is preferably provided in an evacuated outer chamber. The sample may be introduced directly into the source chamber 1 or with the assistance of a carrier gas such as helium. The sample is preferably exposed to a high temperature oxidising surface of the ion repeller electrode 6 which preferably causes the sample to be oxidised to yield the oxides of the elements contained within the sample molecule. For example, carbon in the organic molecule is preferably converted to one or more oxides of carbon, preferably to carbon dioxide. Similarly, hydrogen is preferably converted to water and nitrogen is preferably converted to one or more oxides of nitrogen. Sulphur is preferably converted to one or more oxides of sulphur (e.g. sulphur dioxide) and phosphorus is preferably converted to one or more oxides of phosphorus. Fluorine is preferably converted to one or more oxides of fluorine (e.g. fluorine monoxide) and chlorine is preferably converted to one or more oxides of chlorine (e.g. chlorine dioxide). Bromine is preferably converted to one or more oxides of bromine or to free bromine. The resulting molecules of the oxidation process are then preferably ionised by electron impact ionisation with the electron beam 3 and the resultant ions are preferably extracted from the source chamber 1 through the ion exit aperture 5. The ions are then preferably passed on to a mass spectrometer for mass analysis.
The mass spectrometer downstream of the ion source may, for example, comprise a quadrupole mass filter or a quadrupole ion trap. However, a mass spectrometer capable of high resolution is particularly preferred since some of the product ions may have substantially the same nominal mass. For example, carbon dioxide (CO2) and nitrous oxide (N2O) both have a nominal mass of 44. However, their accurate masses are 43.990 and 44.001 respectively and hence these ions will be resolved at a mass resolution of 4000. According to the preferred embodiment a high resolution mass spectrometer may be provided such as a double focusing magnetic sector mass analyser, a Time of Flight (“TOF”) mass analyser, an orthogonal acceleration Time of Flight (“oa-TOF”) mass analyser, a Fourier Transform Ion Cyclotron Resonance (“FT-ICR”) mass analyser or a Fourier Transform electrostatic trap mass analyser such as an Orbitrap® mass analyser. In particular, Time of Flight, FT-ICR and Orbitrap® instruments may be used as they have parallel detection characteristics and are capable of recording mass spectra with very high sensitivity.
According to the preferred embodiment the source chamber 1 is preferably heated, preferably to at least 400° C. The source chamber 1 is preferably contained in a vacuum chamber which is preferably maintained at a very low pressure. The vacuum is preferably maintained at a pressure of less than 10−6 mbar, preferably at a pressure of less than 10−7 mbar, further preferably at a pressure of less than 10−8 mbar, and further preferably at a pressure of less than 10−9 mbar. A high vacuum is preferred to minimise the residual background gas pressure which will contribute to the mass spectrum and which may interfere with the peaks resulting from oxidation of the sample. In particular, a background pressure of water will interfere with the water signal generated from the oxidation of the organic compound. The use of a carrier gas, such as helium, may advantageously be used to purge the source chamber 1 of residual background gas. The carrier or purging gas is preferably of high purity and is dry.
The oxidising reagent may slowly become degenerated and hence according to an embodiment of the present invention the oxidising surface may periodically be recharged. This may be accomplished by introducing oxygen via the sample or purging gas inlet line 2 for a period of time while the oxidising surface is preferably maintained at an appropriate temperature. This method of recharging is preferred to that of removing the electrode from the vacuum chamber since once the high vacuum is lost then it may take a considerable period of time to recover.
Analysis of the resultant mass spectrum enables an approximate determination of the elemental composition of the organic compound to be made. According to an embodiment the background spectrum due to the residual background gas may be subtracted in order to determine the true spectrum due to the oxidation of the organic compound. It may also be necessary to calibrate the response of the ionisation source and the mass analyser for each component in the mass spectrum by means of an appropriate reference material or standard. This will allow a response factor for each component to be determined and this in turn will allow each measurement to be corrected for different response factors. Once an approximate elemental composition has been determined this information may be used in combination with the measured mass of the molecules of the organic compound, or preferably the accurate measured mass of the organic compound, to determine the elemental composition of the organic compound.
An Electron Impact ionisation ion source according to an embodiment of the present invention which is shown in
In the embodiment illustrated in
Introduction of the organic sample material in the form of a beam of ions 10 allows a very significant increase in the range and variety of species that may be analysed according to the preferred embodiment of the present invention. Nearly all organic materials may be ionised and transmitted through a vacuum chamber regardless of the chemical polarity, volatility and stability of the organic material. An organic material needs to be reasonably volatile and stable and therefore have low or zero chemical polarity in order to be introduced in the gas phase into the embodiments illustrated in
Depending on the characteristics of the organic sample the sample material may be ionised by one or more of the following ionisation methods that may be used within a vacuum including Electron Impact (“EI”) ionisation, Photo Ionisation (“PI”) ionisation, Field Ionisation (“FI”) ionisation, Field Desorption (“FD”) ionisation, Chemical Ionisation (“CI”) ionisation, Fast Atom Bombardment (“FAB”) ionisation, Surface Ionisation Mass Spectrometry (“SIMS”) ionisation, Liquid Surface Ionisation Mass Spectrometry (“LSIMS”) ionisation or, Plasma Desorption (“PD”) ionisation. Thermospray ionisation, Laser Desorption Ionisation (“LDI”), Matrix Assisted Desorption Ionisation (“MALDI”) and Desorption Ionisation On Silica (“DIOS”) ionisation may also be used.
Depending on the characteristics of the organic sample the material may be ionised by one or more ionisation methods at substantially atmospheric pressure. For example, Electrospray ionisation (“ESI”), Atmospheric Pressure Chemical Ionisation (“APCI”), Atmospheric Pressure Photo-Ionisation (“APPI”), Atmospheric Pressure Laser Desorption and Ionisation (“AP-LDI”), Atmospheric Pressure Matrix Assisted Laser Desorption and Ionisation (“AP-MALDI”), Desorption Electrospray Ionisation (“DESI”), Direct Analysis in Real Time (“DART”), Atmospheric Pressure Ionisation (“API”), Ni63 ionisation and other sampling and ionisation techniques that may be used at atmospheric pressure may be used.
If the sample comprises a mixture of different organic compounds then it may first be separated into its components prior to ionisation. According to an embodiment separation techniques such as Gas Chromatography (“GC”), Liquid Chromatography (“LC”), Capillary Electrophoresis (CE), Capillary Electrophoresis Chromatography (CEC), Ion Mobility Separation (“IMS”), Differential Mobility Separation (“DMS”), Field Asymmetric Ion Mobility Separation (“FAIMS”) and other techniques that may be interfaced directly to the ionisation source may be used. The process whereby the sample is ionised at atmospheric pressure by ionisation techniques such as Electrospray ionisation or Atmospheric Pressure Chemical Ionisation and wherein the resultant ions are then passed through into a first vacuum chamber of a mass spectrometer is known for interfacing liquid chromatography and capillary electrophoresis to mass spectrometry. According to an embodiment solvent is removed from organic samples that are in solution and therefore this process solves the problem of the need to remove solvent from organic sample material prior to analysis by mass spectrometry.
A further advantage of ionising the organic sample material prior to oxidising with a heated oxidising surface 8 is that the ion beam 10 may be filtered by mass to charge ratio and/or by ion mobility prior to analysis. An ion source may comprise a number of different ionic species. A mass filter such as a quadrupole mass filter, a magnetic sector or a Wien filter may be used to select just one ionic species of interest. Furthermore, if required, just one isotope peak from the ionic species of interest may be selected. The ability to select one isotope or another can be helpful in removing any ambiguities in the interpretation of a mass spectrum of the oxidised or fluorinated products of the organic molecule.
Another advantage of ionising the organic sample material prior to oxidising with a heated oxidising surface 8 is that the ion beam 10 may first be subjected to fragmentation to produce one or more characteristic fragment, daughter or product ions. The fragment or product ions may themselves be the subject of analysis. The fragment or product ions may be accurately mass measured and may also be submitted to elemental analysis according to the preferred method described here. Such species are not available for analysis by any other technology and the opportunity to submit such species to elemental analysis is particularly advantageous. Methods for fragmentation of ions include Collision Induced Decomposition (“CID”) in a gas collision cell, preferably employing radial confinement of ions by means of RF ion guides. Other methods include Electron Capture Dissociation (“ECD”), Electron Transfer Dissociation (“ETD”), Surface Induced Decomposition (“SID”) and other known methods employing reagent atoms, molecules, ions and/or metastable atoms, metastable molecules and metastable ions. Following fragmentation of sample ions it may be advantageous to select one fragment, daughter or product ion according to its mass to charge ratio and/or its ionic mobility prior to analysis according to a preferred method of the present invention. A mass filter, such as a quadrupole mass filter, a magnetic sector or a Wien filter may be used to select just one ionic species of interest. Alternatively, or in addition, an ion mobility separator may be used to select an ion of interest prior to analysis.
In
The mass spectrometer downstream of the ion source may comprise a quadrupole mass filter or a quadrupole ion trap. However, a mass spectrometer capable of high resolution may be provided since some of the product ions may have the same nominal mass. Such high resolution mass spectrometers include double focusing magnetic sector mass analysers, Time of Flight (“TOF”) mass analysers, orthogonal acceleration Time of Flight (“oa-TOF”) mass analysers, Fourier Transform Ion Cyclotron Resonance (“FT-ICR”) mass analysers and Fourier Transform electrostatic trap mass analysers such as an Orbitrap® mass analyser.
In
According to a preferred embodiment the ion source chamber 1 is preferably heated, preferably to at least 400° C., and is preferably contained in a vacuum chamber which is preferably maintained at a very low pressure. The vacuum may, for example, be maintained at a pressure of less than 10−7 mbar, preferably at a pressure of less than 10−8 mbar, and further preferably at a pressure of less than 10−9 mbar. A high vacuum is preferably provided in order to minimise the residual background gas pressure and in particular the partial pressure of water. A high purity and dry carrier gas, such as helium, may advantageously be used to purge the ion source chamber 1 of residual background gas.
Analysis of the mass spectrum of the oxidised organic sample allows an approximate determination of the elemental composition of the organic compound to be made. It may be necessary to subtract the background spectrum due to the residual background gas and to correct the measured peak intensities to allow for different response factors due differences in ionisation, mass analyser transmission and detection efficiencies. The approximate elemental composition may then be used in combination with the measured mass or mass to charge ratio, preferably the measured accurate mass or mass to charge ratio, of the organic compound of interest to determine its elemental composition.
An advantage of the embodiment illustrated in
An additional advantage of the embodiment illustrated in
In order to test the combustion of an organic molecule in the vacuum system of a mass spectrometer, experiments were carried out using acetophenone. Acetophenone is a liquid at room temperature but it is quite volatile and when a small volume is introduced into an evacuated reservoir heated to 100° C. then it becomes gaseous.
In order to produce a copper oxide (CuO) surface to the copper ion repeller 6, oxygen was introduced into the ion source 1 through the gas inlet line normally used for introducing CI reagent gas. The temperature at which copper oxide thermally decomposes under vacuum is known to be significantly lower than that at atmospheric pressure (see Thermal decomposition of cupric oxide in vacuo; Proc. Phys. Soc., B70, 1005-1008, 1957) and as a consequence it was not certain that the copper could effectively be oxidised under vacuum. Hence, in order to oxidise the copper surface it was exposed to a low pressure of oxygen gas at a series of different temperatures. The oxygen pressure measured on a Penning gauge in the vacuum housing was 10−5 mbar and it was estimated that the oxygen pressure within the ion source chamber 1 was about 10−3 mbar. The ion source chamber 1 and the ion repeller 6 were heated to about 400° C. for about an hour. The temperatures were then reduced to about 300° C. for a further hour and then further reduced to about 200° C. for a further hour. The flow of oxygen gas into the source was then switched off.
Acetophenone (C8H8O) was then introduced continuously into the ion source 1 from a heated reservoir through a heated fine capillary 2. The ion source chamber 1 was maintained at 200° C. Spectra were recorded every two seconds whilst the copper/copper oxide ion repeller 6 was progressively heated from 200° C. to 700° C. over a period of approximately 20 minutes.
For comparison, the same experiment was repeated, but without the process of introducing oxygen in order to oxidise the copper ion repeller 6.
Comparison of the chromatogram for carbon dioxide shown in
Comparison of the two background subtracted spectra shown in
The lower temperature at which the copper oxide appears to decompose thermally in vacuum, when compared with its thermal decomposition at atmospheric pressure is in agreement with the observations reported by Goswami and Trehan (Thermal decomposition of cupric oxide in vacuo; Proc. Phys. Soc., B70, 1005-1008, 1957). The use of other oxide surfaces with higher temperatures of thermal decomposition in vacuum may be preferred. The presence of a background signal due to the presence of water illustrates a difficulty with this method. According to an embodiment a heated fluorinating reactive surface may be used in order to overcome this difficulty.
The prime objective of the preferred embodiment of the present invention is to provide a universal means for determining the approximate elemental composition of organic compounds, with improved sensitivity and improved speed, and to use this information along with a measurement of the mass of the organic molecules in question to determine their elemental composition. However, the preferred embodiment of the present invention may also be used to measure the isotope ratio of the elements in organic compounds. The organic compound is preferably oxidised to the oxides of the constituent elements and these may be submitted to mass analysis. Alternatively, the organic compound may be fluorinated or chlorinated. This also allows measurement of the isotope ratios of the constituent elements.
The ion sources according to embodiments of the present invention as illustrated in
Furthermore, if the sample comprises a mixture of different organic compounds then it may first be separated into its components prior to ionisation. Such separation techniques include Gas Chromatography (“GC”), Liquid Chromatography (“LC”), Capillary Electrophoresis (“CE”) and other well known techniques. The process whereby the sample is ionised at atmospheric pressure by ionisation techniques such as Electrospray Ionisation (“ESI”) and Atmospheric Pressure Chemical Ionisation (“APCI”) is a well established method for interfacing liquid chromatography and capillary electrophoresis to mass spectrometry. This process incorporates the stage of removing the solvent from organic samples that are in solution and therefore inherently solves the problem of removing solvent from organic sample material prior to analysis of the isotope ratios of its constituent elements.
In applications where it is required to measure isotope ratios it is generally preferred to use a magnetic sector mass spectrometer fitted with several detectors, one for each isotope mass to be measured. This allows all the required isotope peaks to be measured simultaneously. However, isotope ratio measurements may also be made using a quadrupole mass spectrometer or another type of mass spectrometer.
Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0813060.1 | Jul 2008 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2009/001753 | 7/16/2009 | WO | 00 | 4/1/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61082249 | Jul 2008 | US |
