Portable polarographic analyzer and quick polarographic determinations

• US 3,922,205 A
• Filed: 10/01/1974
• Issued: 11/25/1975
• Est. Priority Date: 08/20/1973
• Status: Expired due to Term

• Current Assignee: James D. Mclean, John F. Holland
• Original Assignee: James D. Mclean, John F. Holland
• Inventors: Holland, John F., McLean, James D.
• Primary Examiner(s): Kaplan, G. L.
• Application Number:
  US05/510,964
• Time in Patent Office: 420 Days
• Field of Search: 204/1T,195H,195R,195P
• US Class Current: 205/782
• CPC Class Codes: G01N 27/48 using polarography, i.e. measuring changes in current under a slowly-varying voltage
• CPC Class Codes: G01N 33/0047 Organic compounds

Abstract

compounds, such as aldehydes, by reacting the test sample in aqueous medium with a hydrazine acid addition salt at a pH of about 3 to 6.5 to form the hydrazone in aqueous medium which is detectable with great sensitivity and specificity. The working electrode may be underlying or may be suspended, but in any event, is best replaced or renewed or cleaned between determinations. In an embodiment that is especially useful for carrying out polarographic analysis in non-aqueous, but conducting, medium there is employed a third electrode, a counter electrode, and the special circuit includes an operational amplifier electrically connected to each of the counter electrode and the reference electrode in such a way that the reference electrode is nonworking and relatively non-variant, the current flow in the cell being between the working electrode and the counter electrode as monitored and controlled in response to the reference electrode.

A special purpose portable polarographic instrument and method for the rapid repetitive quantitative determination of polarographically reactive species in aqueous solution utilizing a sample cell in which are placed a conducting sample solution, a suitable reference electrode and a fixed area working electrode and, connected to the electrodes, a special circuit for (1) impressing across the cell a reducing or oxidizing voltage throughout a time linear pre-selected range of scanning potential, (2) proportionately converting the consequent current flow to a potential, and (3) measuring the potential. The maximum potential is retained in a peak seeking voltage circuit and is read on a voltmeter in a voltage follower circuit. The polarographic test utilizing the instrument is made more specific for

Claims

1. A SPECIAL PURPOSE POLAROGRAPHIC INSTRUMENT FOR THE RAPID REPETITIVE QUANTITATIVE DETERMINATION OF A POLAROGRAPHICALLY REACTIVE SPECIES IN AN ELECTROLYTE SOLUTION IN THE SUBSTANTIAL ABSENCE OF INTERFERING SUBSTANCES, WHICH CONSISTS ESSENTIALLY OF, IN COMBINATION:

A HOLLOW NON-CONDUCTING CELL BODY IN THE FORM OF A RECEPTACLE ADAPTED TO RECEIVE ABOUT 5 TO 25 MILLIMETERS OF SAMPLE ELECTROLYTE SOLUTIONS;

A FIXED AREA WORKING ELECTRODE POSITIONED SO AS TO PHYSICALLY AND ELECTRICALLY CONTACT SAID ELECTROLYTE SOLUTION PLACED IN SAID CELL;

A REFERENCE ELECTRODE ADAPTED TO BE POSITIONED EXTENDING INTO SAID CELL TO A SUFFICIENT DEPTH TO HAVE THE SENSING END IMMERSED IN SAID ELECTROLYTE SOLUTION WHEN THE CELL IS IN USE;

MEANS FOR SUPPORTING THE SAID REFERENCE ELECTRODE WITH THE SENSING END THEREOF WITH THE CELL BODY;

MEANS FOR ELECTRICALLY CONNECTING EACH OF THE REFERENCE ELECTRDOE AND THE WORKING ELECTRODE, RESPECTIVELY, TO SPECIAL CIRCUITRY TO MAKE A COMPLETED OPERATIVE CIRCUIT;

SAID SPECIAL CIRCUITRY EMBODYING (1) MEANS FOR AUTOMATICALLY IMPRESSING FOR A PRESELECTED TIME INTERVAL DURING EACH SAID DETERMINATION, A CONTINUOUS, LINEAR SCANNING POTENTIAL ACROSS THE ELECTRODES IN THE CELL THROUGHOUT A PRESELECTED VOLTAGE RANGE SUFFICIENT TO CAUSE TO GRAPHICALLY QUANTITATIVELY REACT SPECIES TO BE QUANTITATIVELY DETERMINED WHEREBY A CONTINUOUS UNPULSED CURRENT FLOWS BETWEEN THE ELECTRODES DURING SAID TIME INTERVSAL THE CURRENT FLOW BEING PROPORTIONAL TO THE NUMBER OF IONS OR MOLECULES POLAROGRAPHICALLY REACTED;

(20 MEANS FOR AUTOMATICALLY PROPORTIONALLY CONVERTING THE CURRENT FLOW TO A POTENTIAL;

(3) A CIRCUIT PORTION HAVING PEAK VALUE MEANS INCLUDING A CAPACITOR AND A DIODE IN COMBINATION FOR CAPTURING AND RETAINING THE MAXIMUM POTENTIAL ARISING FROM CONVERSION OF THE CURRENT FLOW;

(4) MEANS INCLUDING A VOLTMETER FOR AUTOMATICALLY MEASURING SAID MAXIMUM POTENTIAL;

AND (5) MEANS FOR DISCHARGING THE CAPTURED AND RETAINED MAXIMUM POTENTIAL.

2. THE INSTRUMENT AS IN CLAIM 1 WHICH EMPLOYES ADDITIONALLY A THIRD ELECTRODE IN THE FORM OF A COUNTER ELECTRODE AND THE SPCIAL CIRCUITRY EMBODIES AN OPERATIONAL AMPLIFIER, THE REFERENCE ELECTRODE AND THE COUNTER ELCTRODE EACH BEING ELECTRICALLY CONNECTED TO SAID OPERATIONAL AMPLIFIER IN SUCH A MANNER THAT THE REFERENCE ELECTRODE IN A NON-WORKING ELECTRODE THAT IS RELATIVELY NON-VARIANT IN POTENTIAL, THE CURRENT FLOW IN THE CELL WHEN IN USE BEING PRIMARILY BETWEEN THE WORKING ELECTRODE AND THE COUNTER ELECTRODE, THE CURRENT FLOW RESULTING FROM THE POTENTIAL ESTABLISHED BETWEEN THE REFERENCE ELECTRODE AND THE WORKING ELECTRODE.

3. The instrument as in claim 2 wherein the voltmeter is incorporated in a voltage follower circuit.

4. The instrument as in claim 2 wherein the voltmeter is provided with a digital readout.

5. The instrument as in claim 2 wherein the special circuitry embodies means for resetting the scanning potential means.

6. The instrument as in claim 2 wherein the special circuitry includes means for making a residual current correction in connection with the means for converting current flow to potential.

7. The instrument as in claim 2 wherein means is provided for sweeping oxygen from aqueous sample solution in the sample cell and maintaining an inert gas cover over said solution during quantitative determination of polarographically reactive species in said solution.

8. The instrument as in claim 1 wherein the voltmeter is incorporated in a voltage follower circuit.

9. The instrument as in claim 1 wherein the voltmeter is provided with a digital readout.

10. The instrument as in claim 1 wherein the special circuitry embodies single switch means for simultaneously resetting the scanning potential means and initiating said impressing of scanning potential, converting current flow to a potential and measuring such potential.

11. The instrument as in claim 1 wherein the special circuitry includes means for making a residual current correction in connection with the means for converting current flow to potential.

12. The instrument as in claim 1 wherein means is provided for sweeping oxygen from sample electrolyte solution in the sample cell and maintaining an inert gas cover over said solution during quantitative determination of polarographically reactive species in said solution.

13. The instrument as in claim 1 wherein the instrument is adapted to quantitatively determine reducible species.

14. The instrument as in claim 1 wherein the fixed area working electrode is a quiescent mercury pool.

15. The instrument as in claim 1 wherein the fixed area working electrode is a hanging drop of mercury.

16. The instrument as in claim 1 wherein the reference electrode is a calomel electrode.

17. The instrument as in claim 1 wherein the reference electrode is a silver-silver chloride electrode.

18. THE POLAROGRAPHIC METHOD OF QUANTITATIVELY DETERMINING A POLAROGRAPHICALLY REACTIVE SPECIES ON CONDUCTING SAMPLE SOLUTION IN THE SUBSTANTIAL ABSENCE OF INTERFERING POLARGRAPHICALLY REACTIVE SUBSTANCES WHICH COMPRISES:

PLACING IN A NON-CONDUCTING SAMPLE CELL BODY FROM ABOUT TO ABOUT 25 MILLITERS OF SAMPLE SOLUTION CONTAINING A QUANTITY OF POLAROGRAPHICALLY REACTIVE SPECIES LESS THAN AN AMOUNT WHICH EXCEED THE LINEAR RESPONSE RANGE OF SAID INSTRUMENT, THE SAMPLE CELL BODY HAVING POSITIONED THEREIN A REFERENCE ELECTRODE AND A FIXED AREA WORKING ELECTRODE EACH HAVING THE SENSING END THEREOF IMMERSED IN SAID SAMPLE SOLUTION;

SWEEPING OXYGEN GAS FROM THE SAMPLE SOLUTION IN THE CELL AND PROVIDING AN INERT GAS COVER OVER SAID SOLUTION DURING ANALYSIS;

IMPRESSING A SCANNING POTENTIAL BETWEEN SAID ELECTRODES WHICH VARIES LINEARLY WITH TIME THROUGHOUT A RANGE SUFFICIENT TO CAUSE POLAROGRAPHIC REACTION OF SAID POLAROGRAPHICALLY REACTIVE SPECIES WHEREBY A CONTINUOUS UNPULSED CURRENT FLOWS BETWEEN THE ELECTRODES;

PROPORTIONALLY CONVERTING THE RESULTANT CURRENT FLOW INTO A POTENTIAL THE MAXIMUM OF WHICH IS STORED BY MEANS OF A CIRCUIT PORTION INCLUDING A DIODE AND A CAPICITOR;

AND MEASURING SAID STORED POTENTIAL BY VOLTMETER MEANS.

19. The method as in claim 18 wherein the polarographically reactive species are reducible species.

20. The method as in claim 19 wherein the reducible species is an organic compound containing the

21. The method as in claim 20 wherein the aqueous sample solution is buffered to about pH 4 and sufficient soluble acid salt of hydrazine is added to convert substantially all the reducible species to the hydrazone and the potential range scanned is about -0.6 to about -1.2 volts.

22. The method as in claim 20 wherein the concentration of reducible species placed in the sample cell does not exceed about 10 parts per million.

23. The method as in claim 19 wherein oxygen is swept from the sample solution by inert gas sparging before commencing analysis and an inert gas cover is maintained over the sample solution during analysis.

24. The method as in claim 18 wherein the said capacitor means is discharged after measuring the stored potential and another quantity of another sample solution containing polarographically reactive species is placed in said sample cell and the concentration of the species polarographically quantitatively determined as in claim 18.

25. The method as in claim 18 wherein the built up potential is measured by voltmeter means with digital readout.

26. THE METHOD OF RAPID QUANTITATIVE POLAROGRAPHIC DETERMINATION OF POLAROGRAPHICALLY REACTIVE SPECIES IN SAMPLE ELECTROLYTE SOLUTION CONTAINING SUCH SPECIES IN THE SUBSTANTIAL ABSENCE OF INTERFERING SPECIES WHICH COMPRISES:

PLACING ABOUT 5 TO ABOUT 25 MILLIMETERS OF SAMPLE ELCTROLYTE SOLUTION IN A HOLLOW NON-CONDUCTING CELL BODY HAVING A FIXED AREA WORKING ELECTRODE, A FIXED AREA COUNTER ELCTRODE AND A REFERENCE ELECTRODE EACH POSITIONED THEREIN SO AS TO HAVE THE SENSING END THEREOF IMMERSED IN THE SAMPLE SOLUTION;

IMPRESSING A CONTINUOUS LINEAR SCANNING POTENTIAL ACROSS EACH OF (1) THE COUNTER ELECTRODE AND THE WORKING ELCTRODE, AND (2) THE REFERENCE ELECTRODE BEING PROVIDED WITH A ELECTRODE, THE REFERENCE ELECTRODE BEING PROVIDED WITH A HIGH IMPEDANCE WHEREBY THE RESULTING CURRENT FLOW IS SUBSTANTIALLY BETWEEN THE COUNTER ELECTRODE AND THE WORKING ELECTRODE AND THE SCAN CONTINUING UNTIL THE POTENTIAL AS MEASURED BETWEEN THE REFERENCE ELECTRODE AND THE WORKING ELECTRODE IS AT LEAST SUFFICIENT TO CUASE SAID SPECIES TO BE DETERMINED TO POLAROGRAPHICALLY REACT, WHEREBY A CONTINUOUS UNPULSED CURRENT FLOWS BETWEEN THE ELECTRODES;

PROPORTIONALLY CONVERTING THE FLOW TO A POTENTIAL THE MAXIMUM OF WHICH IS STORED BY MEANS OF A CIRCUIT PORTION INCLUDING A DIODE AND A CAPACITOR;

AND MEASURING THE STORED POTENTIAL WTH A VOLTMETER.

27. The method as in claim 26 in which the maximum potential obtained, as a result of converting current flow to a potential, is retained until read.

28. The method as in claim 26 in which the sample solution is a non-aqueous solution.