Patent Application
20080087815
In one embodiment of the invention, the sample source 10 includes an analytical separation device 6 that provides a liquid containing a sample of interest from to sample sprayer 9. Similarly, sample source 12 may include an analytical separation device 8 that provides a liquid containing a sample of interest to sample sprayer 11. A sample may be any liquid material, including dissolved solids, or mixture of materials dissolved in a solvent. Samples typically contain one or more components of interest, and may be derived from a variety of sources such as foodstuffs or environmental materials, such as waste water, soil or crop. Samples may also include biological samples such as tissue or fluid isolated from a subject (e.g., a plant or animal), including but not limited to plasma, serum, spinal fluid, semen, lymph fluid, external sections of skin, respiratory, intestinal and genitourinary tracts, tears, saliva, milk, blood cells, tumors, organs and also samples of in vitro cell culture constituents, or any biochemical fraction thereof. Useful samples might also include containing calibration standards or reference mass standards.
The analyte sample(s) may be in liquid or gas form, the sprayers 9 & 11 may be merely gas exits, and the ionization method may vary. However, the preferred mode of sample introduction for medium and large molecules in tandem mass spectrometry is liquid chromatography (LC/MS/MS), by which sample components are sorted according to their retention time on a column through which they pass. The various compounds that leave tubes 6 and 8 and flow into sample supply regions 2 and 4 are present for some tens of seconds or less, which is the amount of time available to obtain all the information about an eluting compound. Since compounds often overlap in their elution, rapid spectral generation as provided by LC/MS/MS may enable rapidly generating each compound's elution profile and allow overlapping compounds to be separately identified.
Analytical separation devices 6 and 8 can be any liquid chromatograph (LC) device including but not limited to a high performance liquid chromatograph (HPLC), a micro- or nano-liquid chromatograph, an ultra high pressure liquid chromatography (UHPLC) device, a capillary electrophoresis (CE), or a capillary electrophoresis chromatograph (CEC) device. However, any manual or automated injection or dispensing pump system may be used. For example, in some embodiments, a liquid stream may be provided by means of a nano- or micro-pump.
A continuous stream of sample provided by analytical separation devices 6 and 8 are then ionized by devices 9 and 11, respectively. Devices 9 and 11 may be any ion source known in the art used for generating ions from an analyte sample. Examples include atmospheric pressure ionization (API) sources, such as electrospray (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) sources.
Ions leaving sample sprayers 9 and 11 are directed to beam converging transfer capillary 15 which transfers ions toward mass analyzer 62 and allows a reduction of gas pressure from that of the ionization source chambers 2 and 4. Pressure may be reduced by one or more vacuum chambers. Capillary 15 may be a tube, a passageway or any other such device for ion transport and pressure reduction. According to an embodiment of the invention, capillary 15 has a first channel including entrance 14 to transfer the first ion stream from sprayer 9, and a second channel including entrance 16 to transfer the second ion stream from sprayer 11. Ions from the first and second ion streams enter their respective channels of capillary 15 from separate inlets at one end of capillary 15, and exit a single outlet 7 at the other end of capillary 15 to converge into a single flight path. In one aspect, the ion inlet device includes a capillary 15 (or tube) that is Y-shaped as shown.
The mass spectrometer system shown in
Ions of the first and second ion streams are combined or converged by capillary 15 into a single flight path in a time division multiplexed manner, e.g., in slots of predetermined time in alternating sequence, as will be further discussed later. The ions in the flight path (including ions from the first and second ion streams) then pass through skimmer 22.
The ions exit skimmer 22 and enter a first or preliminary ion guide 30 in chamber 17. According to an exemplary embodiment of the invention, first ion guide 30 is an octapole ion guide and is driven by power source 34. Ion guide 30 may also be a radio frequency (RF) ion guide or any other type of ion guide such as a direct current (DC) ion guide, a stacked ring ion guide or an ion lens system. Ion guide 30 may also include a multiple structure if the power sources 34 is an RF and/or DC power supplies.
After ions travel along a preliminary ion path through first ion guide 30, they are pushed or directed into a second ion guide 38 in chamber 21. As shown in
According to one embodiment, mass analyzer 62 is used for analyzing ions from both first and second ion streams of the mass spectrometer system, as combined into a single flight path of ions from ion sources 2 and 4. The fragment ions and any undissociated precursor ions from either the first ion stream from ion source 2 or the second ion stream from ion source 4 pass through beam slicer 58 into mass analyzer 62, which determines the m/z ratio of the ions to determine molecular weights of analytes in the samples.
Tandem mass spectrometers may include multiple mass analyzers operating sequentially in space or a single mass analyzer operating sequentially in time. Mass spectrometers that can be coupled to a gas or liquid chromatograph include the triple quadrupole mass spectrometer, which is widely used for tandem mass spectrometry. However, one limitation in the triple quadrupole system is that recording a fragment mass spectrum can be time consuming because the second mass analyzer must step through many masses to record a complete spectrum. To overcome this limitation, the second mass analyzer may be replaced by a time-of-flight (TOF) analyzer. One advantage of the TOF analyzer is that it can record up to 104 or more complete mass spectra every second. Thus, for applications where a complete mass spectrum of fragment ions is desired, the duty cycle is greatly improved with a TOF mass analyzer and spectra can be acquired more quickly. That is, the TOF analyzer can produce product spectra at such a high rate that the full MS/MS spectrum can be obtained in one slow sweep of the quadrupole mass analyzer. Alternatively, for a given measurement time, spectra can be acquired on a smaller amount of sample.
According to one embodiment of the invention, mass analyzer 62 includes a TOF analyzer. As shown in
Ions have different velocities due to different mass-to-charge ratios (m/z) when accelerated in a vacuum by an electric field. Detector 66 measures the time required for the ion to reach the detector after acceleration begins to determine this velocity at the end of the flight path in flight tube 70. For a known distance d between the acceleration region and the detector, and a flight time t between the times of acceleration and detection, the velocity v will be v=d/t (note that where a TOF includes a mirror element, the equation will differ as is well known to one of skill in the art)(note also that since the pulser does not create an infinite gradient, finite time is spent accelerating and this must also modify the equation). Since the distance is approximately the same for all ions, their arrival times differ with smaller m/z ions reaching the detector first and larger m/z ions later. Signal processing electronics then record an ion mass spectrum at time intervals, in a three-dimensional LC/MS/MS or GC/MS/MS data sets.
According to embodiments of the invention, simultaneous analyses of ions from two or more ion streams is enabled by time division multiplexing. That is, signals from two or more sources are simultaneously sent over one transmission path by interleaving pulses of ions from both sources. As noted above, ions in the ion streams corresponding to ion sources 2 and 4 are transferred into a single flight path in slots of predetermined time, in alternating sequence. Ion sources 9 and 11 may be nebulizers connected to separate nebulizer voltages that produce alternating ion streams in short, rapid pulses by switching nebulizer voltages. Alternatively, the nebulizers may be held at a constant voltage such as ground, the voltage applied to the two entrances 14 and 16 of the capillary 15 may be varied to accept and reject ions from the two sources. Timed spaces may also be provided by switching in neutral molecules (e.g., pure solvent, instead of analyte and solvent solution) into the liquid streams, but this in not preferred because it is inherently slow and disruptive. An electrical means of either inhibiting the ion formation or the ion transport prior to combing the streams is preferred. Interaction between ions from sprayers 9 and 11 may thus be avoided due to the timed spacing of pulses of the ion streams. In one aspect, the length of each pulse occupies the entire ion path from the source to the analyzer. The rest of the ion optics in spectrometer 100 generally operate as components of a single channel MS instrument, except that their operating conditions, such as mass range or filtering, may be additionally adjusted to address the requirements of each ion stream independently.
The mass spectrum is then determined by a signal processing system (not shown). In one aspect, pulser 64 accelerates each ion stream independently, and detector 66 detects each ion signal separately so that two separate data files are instantly produced. In another aspect, the signal processing system records a single output data file for the combined inputs of the first ion stream corresponding to ion source 2 and the second ion stream corresponding to ion source 4. The signal processing system coupled to analyzer 62 includes a demultiplexer that subsequently reassembles the single output data file according to their transmission order, to provide two or more data files corresponding to each ion stream.
In other embodiments of the invention, three or four different ion streams from three or four different ion sources may be provided in the same MS or MS/MS instrument and share the same TOF analyzer.
A variety of different mass analyzers using electromagnetic fields and ion optics may be part of the mass spectrometer system in other embodiments of the invention, such as a quadrupole analyzer, a reflection time of flight analyzer, an ion trap analyzer, an ion cyclotron mass spectrometer, Fourier transform ion cyclotron resonance (FTICR), a single magnetic sector analyzer, and a double focusing two sector mass analyzer having an electric sector and a magnetic sector. Other spectrometry systems and variations as known in the art may be used, such as for example coupling electrospray ionization (ESI) to TOF mass spectrometry (TOFMS). Other variations on the TOFMS include subjecting all the precursor ions to the fragmentation mechanism without preselection and determining the product mass with subsequent acceleration. Recent proposals also include resonant excitation in RF-only quadrupoles for CID with fragment mass analysis by TOFMS.
Embodiments of the invention described above provide for the analysis of two or more ion streams from two or more ion sources using a single instrument. The different ion sources may be different types of sources. Thus, embodiments of the invention provide advantages of two or more mass spectrometry systems in a single chassis, using a single mass analyzer. Providing two or more MS/MS systems associated with different ion streams or ion channels in one instrument saves cost by requiring only a single set of vacuum pumps, ion optics, data acquisition electronics, other hardware and industrial design. Two or more MS/MS systems could be obtained for a reduced cost, e.g., approaching the cost of only one system, or three or four MS/MS systems for the cost of two. Additionally, providing two or more MS/MS channels in one instrument saves the time to run two (or more) different analyses at different times, since the single instrument provides for separate functions while sharing much of the electronics and hardware.
While the present invention has been described with reference to the specific embodiments disclosed, the invention is not limited to any particular implementation disclosed herein. For example, a radio frequency ion guide may be a quadrupole, hexapole or other multipole device, as well as a structure of rings or a multipole sliced into several segments as well known in the art. It should be understood by those skilled in the art that various changes may be made and equivalents substituted without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.
