Patent Application
20050282286
The present invention relates to a method for determining the organically bound carbon (TOC).
DE 19616760 A1 discloses a method and an apparatus for the continuous determination of the TOC value. In the method, the sample solution is continuously pumped into a microreactor, heated in the microreactor to a predetermined temperature and the organic compound is continuously converted by oxidation in the sample solution under a defined elevated temperature and defined elevated pressure. The gaseous oxidation products from the sample are then drawn through a membrane by suction and passed into a measuring cell and measured there by a mass spectrometer.
WO 99/42824 A1 describes a method for determining the TOC content in liquids, in which method the sample solution is introduced into a reaction chamber for oxidation of the carbon and is transferred, by liquid entering the reaction chamber from outside, into a measuring cell connected to the reaction chamber. There, the carbon dioxide concentration is determined dynamically in the course of flow through the measuring cell, a base value of carbon dioxide concentration corresponding to the untreated liquid and also a maximum value of carbon dioxide concentration established by the carbon dioxide-enriched liquid in the course of flow through the measuring cell being measured, and then a difference between maximum value and base value being formed. The carbon dioxide concentration is determined on the basis of conductivity measurements.
For determination of the analytical parameter TOC (Total Organic Carbon) in water samples, test kits have existed for some years. For example, test kits have been developed as are described in EP 0 663 239 B1. Using the system described there, the analysis can be carried out rapidly and simply on site by personnel with little training and using inexpensive media. The test kit has two containers designed as cuvettes, that is to say one sample reception container and one analysis container, each of which have container openings at the top which can be closed by screw-on closure caps. The test kit also comprises an adaptor via which the container openings, after the closures have been removed, can be connected together gas tightly. The adaptor is provided with a semipermeable membrane which is permeable to gases and, here, in particular, the constituent to be analysed, and the carrier gas. For this, it can consist, for example, of hydrophobic material. The analysis container can comprise the indicator reagent in preformulated and storable form. Likewise, the sample reception container can also be preformulated with a digestion reagent which converts the constituent to be analysed into the gas form.
DE 10018784 C2 describes a modification of this test kit. Here, the analysis container has a pressure-relief device which is preferably disposed at the end of the analysis container opposite the container opening. Excess carrier gas escapes through the pressure relief device which is only permeable to gases, especially when a liquid is used as indicator reagent.
WO 00/75653 describes an analysis apparatus which consists of two vessels which can be inserted one inside the other. Here, the inner vessel comprises the indicator. The sample to be analysed is located in the outer vessel. Both vessels are connected to one another only via the gas space. By heating, the volatile substances are transported from the sample into the gas phase and, via the gas space, come into contact with the indicator and then produce a change. The change in the indicator is determined by means of transmission of a light beam.
DE 10121999 A1 describes a method for the photometric or fluorimetric determination of volatile substances in solutions. For this, a system is used which has a cuvette which is divided into two zones by an ion-impermeable, gas-permeable membrane. By this means, the cuvette has two separate spaces for sample and digestion solution on the one side and indicator solution on the other.
DE 2534620 A1 discloses a method for determining the inorganic carbon content of aqueous liquids, in which a sample of the liquid to be analysed is introduced together with a carbon-dioxide-free carrier gas into a heated reaction chamber, the inorganic carbon compounds are decomposed by a reaction medium to form carbon dioxide, and the resultant carbon dioxide is fed to a CO2 analyser. Movement of the reaction chamber is not mentioned.
To determine the TOC, it is regularly necessary to remove the inorganic carbon. For instance, DE 19906151 A1, DE 19616760 A1, DE 4307814 A1, DE 10018784 C2, DE 10121999 A1, EP 0663239 B1 and WO 00/75653 disclose that the inorganic carbon compounds can be removed by acidification and subsequent expulsion.
The test kits described which have existed for some years consequently have the following typical operating sequence in the analytical procedure:
The first step, the expulsion of the IC, is generally carried out in the previously known methods as follows:
This described handling is very complex for the user. Apart from this, the necessary cleaning work on the expulsion container and magnetic stirrer harbour the risk of contamination and thus falsification of the later sample analyses.
DE 4307814 A1 discloses, for the removal of the inorganic carbon, setting the sample to be studied to a weak pH of about 2 by means of an acid, e.g. hydrochloric acid, and bubbling the measurement amount by blowing in a gas, e.g. air. As a result of the reaction between the carbonates and the acid, carbon dioxide is formed. The outgassing of the carbon dioxide is achieved by the means that the sample is brought to overflow through an upwards-directed measurement line open at the top and the exiting carbon dioxide including the amount of gas previously blown in is removed. This method is also complex. Apart from this, the risk of inaccuracy of analysis is associated with the fact that water is drained from the container.
It is accordingly an object of the present invention to provide a method for determining the organically bound carbon (TOC) in an apparatus,
By this method the process of conversion and expulsion of the inorganically bound carbon from the sample is to be markedly simplified, and the risks of contamination eliminated. At the same time, test kits are to be provided in which, in the reaction zone, an acidic reagent and/or an oxidizing reagent is already preformulated (packaged ready for use by the manufacturer) and the working step of acidification and/or addition of oxidizing agent to the sample is eliminated. Moreover, only one reaction zone is to be employed, that is to say expulsion of the inorganic carbon and/or oxidation of the organically bound carbon is to be carried out in one and the same reaction container. This also avoids the transfer of the sample to the reaction cuvette. In addition, the use of a magnetic stirring bar is to be avoided. In summary, this means that an object of the present invention is to provide a minimal system in which the inorganic carbon is to be expelled in the reaction zone. By this means a plurality of analyses are to be expelled in parallel.
This object is achieved by means of the fact that in step b), to expel the carbon dioxide formed by conversion of the inorganic carbon, the reaction zone (2) is agitated.
The removal of the inorganic carbon is made possible by adding an acid to the sample.
As acids, use is preferably made of phosphoric acid and sulphuric acid, or buffers derived therefrom. Very particular preference is given to phosphoric acid or the buffers derived therefrom.
By agitating the sample in the reaction zone, processes can be accelerated which contribute to the carbon dioxide being released rapidly into the surroundings from the reaction zone having the acidified sample. These are essentially serial equilibrium processes. These include:
According to the invention, the reaction zone or the reaction vessel is preferably agitated horizontally. However, this does not exclude vertical agitations also being carried out. Particular preference is given to the agitations being horizontal and circular. Likewise, the agitations can also be vertical, horizontal and circular in combination, as is the case, for example, with a tumbling agitation. These agitations produce a shaking, jolting and swinging, tumbling and therefore a vigorous agitation of the reaction zone. Preference is given to agitations which accelerate the abovementioned mixing and transport processes and secondly prevent the sample from spraying out of the reaction zone. Agitations have proved advantageous here which have a centrifugal force component, so that the sample is pressed onto the walls of the reaction zone and, together with the reaction zone structuring described below (for example shoulder), quantitative retention in the reaction zone is ensured. On the inner wall of the reaction zone, chicanes and structures can be mounted, which additionally mix the sample passing above them.
According to the invention, preference is given to the radius of the orbit being between 0.1 and 100 mm, preferably 0.5 and 5 mm. Very particular preference is given to a radius of 2 mm.
The angular frequency is preferably between 0.1 and 1000 Hz, particularly preferably between 1 and 100 Hz. Very particular preference is given to 30 Hz.
In addition to the agitation of the reaction zone which can accelerate the abovedescribed mixing and transport processes, further measures can prevent the sample from being sprayed out of the vigorously agitated reaction vessel.
For this, in a variant preferred according to the invention, a reaction zone or reaction vessel can be used which, below its opening, has a curvature in the form of a shoulder. That is to say the cuvette does not have the same diameter from the bottom to the opening. Rather, the diameter of the vessel constricts towards the opening. It has been found according to the invention that the arrangement of this shoulder completely avoids the sample from being sprayed out as a result of the agitation.
Here, by altering the shaping of the shoulder (for example sharper indentation, additional retention rim), the retention effect can be increased, the mechanical agitation intensified and thus finally the expulsion time shortened. Furthermore, structures can be mounted within the shoulder region which, in a similar manner to a deflection plate, guide the exiting sample back into the reaction zone. Of course, it is also possible to provide the closure of the reaction zone with structures (for example a shoulder).
Owing to the design with shoulder, operation of the reaction zone in vertical or horizontal form is made possible. In particular, the diameter constriction in the region of the shoulder has the advantage that the reaction zone can be agitated horizontally without the reaction solution and/or the sample exiting. In this case, all abovedescribed agitations are possible. Preferably, agitation can be about the axis of rotation. In this case, a liquid film forms on the inner wall of the reaction zone, which causes an accelerated gas exchange. Furthermore, other agitations in horizontal and vertical direction are also possible, for example jolting and rocking.
In a particularly inventively preferred variant, the reaction zone is used in an apparatus which may receive one or more reaction zones. This apparatus carries out the described agitations. By using the described apparatus for a plurality of reaction zones, parallel preparation of a plurality of samples for analysis is made possible. In the conventional methods, the sample preparation was time-consuming, inter alia, also because some of the typical users regularly had only a single magnetic stirrer available. The simultaneous makeup and/or the simultaneous preparation of a plurality of samples for analysis was therefore impossible. That is to say, in the previously known method for sample preparation by means of magnetic stirrer and conical flask, a majority of samples could only be prepared in sequence and thus in a significantly more time-consuming manner.
The described inventive acidification of the sample for conversion of the inorganic carbon into carbon dioxide now makes a significantly simpler handling of samples possible. In particular, it is now possible that, in the reaction zone, an acidic solution already preformulated can be supplied in finished package form by the manufacturer. The working step of acidification in a separate vessel, for example in a conical flask, by a magnetic stirrer, is eliminated completely. The cleaning and flushing of the conical flask, which is labour-consuming and time-consuming is likewise eliminated. Advantageously, acidification and subsequent conversion of the inorganic carbon and also subsequent conversion of the organically bound carbon into carbon dioxide can be carried out in one and the same reaction zone. The typical problems which are associated with unsatisfactory cleaning of the vessels (that is to say of the conical flasks used in the acidification), are thus avoided according to the invention.
The invention thus also relates to a test kit for determining the organically bound carbon (TOC) which comprises at least one reaction vessel or one reaction zone, the reaction zone comprising substances for producing carbon dioxide from the sample in preformulated and storable form and the detection zone comprising at least one gas-sensitive reagent in solid or liquid, and also preformulated and storable, form. The reaction zone is distinguished in this case in that it comprises, in preformulated form, acids for converting the inorganic carbon into carbon dioxide.
Preference is given to an embodiment in which the reaction zone in addition also comprises substances in preformulated and storable form for the conversion (oxidizing agent) of the TOC present in the sample to the gaseous carbon dioxide for the step d) to be carried out later. In this case, special measures can be taken to prevent the oxidizing agents present during the expulsion of the inorganic carbon in step b) from already converting TOC into carbon dioxide:
According to the invention, it is not excluded, however, in this case that the preformulated and gas-sensitive reagents and also substances for the conversion into carbon dioxide are stored outside the reaction zone or reaction vessel or detection zone or detection vessel and are not placed into the zones or vessels until the actual case of use. This applies in particular to the substances which are introduced into the reaction zone or the reaction vessel. Here, according to the invention, after addition of the sample, first the acid for the conversion and expulsion of the inorganic carbon can be added. Not until after completion of this reaction is the conversion of the organically bound carbon into carbon dioxide then carried out.
In a further variant of the inventive method, an air stream is passed via the opening of the reaction zone or reaction vessel. By this means, to a certain extent a suction action is generated so that the expulsion of the carbon dioxide from the opening of the reaction zone or reaction vessel is accelerated. Preferably, prepurified ambient air is used for this.
The air can be agitated in the simplest case by disposition of a fan. It is likewise possible, however, to pass a targeted air current over the opening of the reaction zone or reaction vessel by means of a nozzle. Owing to the associated higher velocity of the air stream, a further acceleration of the transport of the carbon dioxide gas from the reaction zone or reaction vessel can be achieved.
Likewise, however, it is also possible to accelerate the gas discharge via a pulsed air stream. Such a pulsation can be achieved, in the simplest case, by a continuous deflection of the air stream being performed in consequence of the agitations of the reaction zone or reaction vessel. In this case, by means of the pulsation, likewise, the sample situated in the reaction zone can be agitated in a pulsed manner, an additional mixing in the liquid sample being performed, which in turn leads to an accelerated expulsion.
The invention will be described in more detail below with reference to the drawings:
In a particular embodiment, reaction zone and detection zone can be connected to one another via a membrane 12.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 028 270.6 | Jun 2004 | DE | national |
| 10 2004 038 607.2 | Aug 2004 | DE | national |
