METHOD AND DEVICE FOR DETERMINING AT LEAST ONE ANALYTE SPECIES IIN AN ANALYTE SOLUTION

Abstract

The invention relates to a method and a device for determining at least one analyte species in an analyte solution, preferably in n analyte solutions consecutively, a computer program comprising instructions related to the program and a computer readable medium having stored such computer program. The method involves a step of amperometric detection followed by cleaning the working electrode on-line by applying at least one cyclic electric potential to the working electrode.

Claims

1. A method for determining at least one analyte species in an analyte solution, comprising: a) carrying out a chromatographic separation of an analyte solution; b) conveying the eluate from the chromatographic separation through an electrochemical flow-through cell, having a working electrode, a counter electrode and a reference electrode; c) determining the amount of and/or the concentration of the at least one analyte species in the eluate by amperometric detection; and d) cleaning the working electrode on-line by applying at least one cyclic electric potential to the working electrode.

2. The method according to claim 1, wherein the method is for determining at least one analyte species in a series of a analyte solutions, comprising the first analyte solution and up to n analyte solutions in total, wherein the steps a) to d) are performed for each of the analyte solutions in the series, adding up to a total of n performances.

3. The method according to claim 1, wherein the method is automated.

4. The method according to claim 1, wherein the amperometric detection is performed in direct current (DC) or pulsed (PAD) mode.

5. The method according to claim 1, wherein the at least one analyte species is an ion.

6. The method according to claim 1, wherein the working electrode is a gold electrode.

7. The method according to claim 1, wherein the reference electrode is an Ag/AgCl electrode.

8. The method according to claim 4, wherein the constant potential in DC-mode is from −1.5 to 1.3V.

9. The method according to claim 1, wherein the minimum potential applied to the working electrode in the electrical potential cycle is not lower than −1.1 V and not higher than 1.1 V.

10. The method according to claim 1, wherein a sweep rate in the cyclic electric potential is not higher than ±1 V/s.

11. The method according to claim 1, wherein the eluent is degassed.

12. A device for determining at least one analyte species in a first analyte solution the device comprising an ion chromatographic separation unit, an electrochemical flow-through cell, and means adapted to execute a), b), c) and d) of claim 1.

13. A computer program comprising instructions to cause the device of claim 12 to execute a), b), c) and d) of claim 1.

14. A computer-readable medium having stored thereon the computer program of claim 13.

15. The method according to claim 1, wherein the amperometric detection in step c) is a chronoamperometric detection.

16. The method according to claim 4, wherein the amperometric detection is performed in direct current mode (DC).

17. The method according to claim 5, wherein the ion is a non-metal ion.

18. The method according to claim 17, wherein the non-metal ion is selected from the group of sulfite (SO.sub.3.sup.2−), cyanide (CN.sup.−), sulfide (S.sup.2−) and iodide (I.sup.−).

19. A device for determining at least one analyte species in a first analyte solution, the device comprising an ion chromatographic separation unit, an electrochemical flowthrough cell and means adapted to execute a), b), c) and d) of claim 9.

20. A computer program comprising instructions to cause the device of claim 19 to execute a), b), c) and d) of claim 9.

Description

[0034] The Figures show the following:

[0035] FIG. 1: Schematic view of a device for determining at least one analyte species in n analyte solutions according to the invention;

[0036] FIG. 2: Schematic view of the electrode arrangement in an electrochemical flow-through cell according to the invention;

[0037] FIG. 3: Exemplary chromatogram obtainable by means of a method or a device according to the invention.

[0038] FIG. 1 presents a schematic view of a device for determining at least one analyte species in n analyte solutions according to the invention. A plurality of samples containing sulfite (SO.sub.3.sup.2−) were stabilized in a solvent of 1 mM formaldehyde/0.02 mM NaOH, kept at a temperature of 6° C., and provided by sample changer 1. The device further has an ion chromatographic column 2. In the present example, column “Metrosep Carb 2-150/4.0” commercially available from Metrohm was used. The eluent used for the chromatographic separation is provided in container 3. In the present example, 300 mM NaOH/300 mM sodium acetate was used. The eluent was degassed in degasser 4. Eluent was conveyed to the injection valve 5 by means of high pressure pump 6. In rinsing mode, eluent and/or any reference solution can be transferred directly to the chromatographic column 2 and on to detector 7. Detector 7 comprises an electrochemical flow-through cell for amperometric detection of the ions of interest.

[0039] FIG. 2 represents a schematic view of the electrode arrangement in an electrochemical flow-through cell 8 according to the invention. The electrochemical flow-through cell 8 has a working electrode 10 of gold, a counter electrode 11 of stainless steel and a reference electrode 13 of Ag/AgCl (wall-jet electrodes).

[0040] When carrying out the chromatographic separation of the sample solution, the sample solutions were injected onto the separation column (3 μL injection volume), chromatography was performed (0.5 mL/min), and the separated analyte species 9 were injected continuously into the electrochemical cell. The set potential for the electrochemical cell was 0.3 V, in direct current measuring mode. Chromatography and amperometric detection were both performed at temperatures of 35° C. The electrolysis current was measured and plotted as a function of time to give a chromatogram.

[0041] FIG. 3 represents chromatogram obtainable by means of the exemplary method and device. The x-axis shows time (in min) and the y-axis a current (in μA). The peaks in current were compared to a calibration function previously generated and peak 14 was identified as pertaining to sulfite.

[0042] The device shown in FIG. 1 is configured to perform a series of sequences as described above in a fully automated way. The device comprises means (not shown) adapted to execute the steps of the method according to the invention n times. In particular, the means include a computer running a computer program with instructions to cause the device to apply different chromatographic stages and amperometric modes. By means of such computer program, the cleaning steps following the measuring steps can be steered, such that the working electrode is cleaned on-line, i.e. immediately following detection, by applying a cyclic electric potential. In the present example, each cyclic electric potential started from a minimum value of −0.6 V and increased with a sweep rate of 0.1 V/s up to a maximum voltage of 0.7 V, where the ramp was inversed. The potential was decreased with a sweep rate of −0.1 V/s.

[0043] The described electric potential cycle was repeated five times after each determination sequence. After the last cleaning cycle, the next determination sequence automatically started for a second analyte solution. No polishing of the electrodes or recalibration in-between sequences is required.