POLAROGRAPH APPARATUS

• US 3,644,824 A
• Filed: 02/09/1970
• Issued: 02/22/1972
• Est. Priority Date: 02/09/1970
• Status: Expired due to Term

• Current Assignee: Anthony Gerald Pope, Arthur William Gardner, Geoffrey Cecil Barker
• Original Assignee: Anthony Gerald Pope, Arthur William Gardner, Geoffrey Cecil Barker
• Inventors: Barker, Geoffrey Cecil, Gardner, Arthur William, Pope, Anthony Gerald
• Primary Examiner(s): Lynch, Michael J.
• Application Number:
  US05/009,908
• Time in Patent Office: 743 Days
• Field of Search: 324/31,30,29 204/195R,195H
• US Class Current: 324/440
• CPC Class Codes: G01N 27/48 using polarography, i.e. measuring changes in current under a slowly-varying voltage

Abstract

Polarographic cell impedance components which are potential dependent are detected by applying a high-frequency and a lowfrequency voltage simultaneously across the cell. The variation in impedance produced by the low-frequency voltage results in amplitude modulation of the high-frequency current through the cell. The amplitude modulation is detected. The impedance components thus indicated comprise principally the faradaic impedance and the double-layer electrode capacity. The doublelayer electrode capacity is compensated by inserting an inductor, preferably variable, in series with the cell so as to resonate at the high frequency with the double-layer electrode capacity.

Claims

1. A polarographic apparatus comprising a polarographic cell, a direct voltage generator connected to supply a direct voltage across the cell, a low-frequency alternating voltage generator connected to supply a low-frequency alternating voltage across the cell, a high-frequency alternating voltage generator connected to supply a high-frequency alternating current to the cell so that in operation the said direct voltage, the said lowfrequency alternating voltage and the said high-frequency alternating current are each supplied independently to the cell, and such that the high-frequency alternating voltage developed across the cell is amplitude modulated as a result of variations in cell impedance produced by the effect of the low-frequency alternating voltage upon such component of the cell impedance as is potential dependent, means for separating from the complex voltage developed across the cell a signal corresponding to the amplitude modulation due to the faradaic component of cell impedance, and indicating means responsive to the said signal.

2. A polarographic apparatus comprising a polarographic cell, a direct voltage generator connected to supply a direct voltage across the cell, a low-frequency alternating voltage generator connected to supply a low-frequency alternating voltage across the cell and a high-frequency alternating voltage generator connected to supply a high-frequency alternating current to the cell so that in operation the said direct voltage, the said low-frequency alternating voltage and the said high-frequency alternating current are each supplied independently to the cell and such that the high-frequency voltage developed across the cell is amplitude modulated as a result of variations in cell impedance produced by the effect of the low-frequency voltage upon that component of the cell impedance which is potential dependent, compensating means included in the electrical circuit of the cell for compensating at least partially for the effect of that part of the potential dependent impedance component which is nonfaradaic and indicating means responsive to a signal derived from the said amplitude modulation as compensated by the compensating means.

3. A polarographic apparatus as claimed in claim 2, comprising a polarographic cell with a dropping mercUry electrode, wherein the compensating means is adapted to compensate at least partly for the double-layer capacity of the dropping mercury electrode.

4. A polarographic apparatus as claimed in claim 3, wherein the said compensating means comprises an inductive device connected in series with the cell, the inductance of the device forming, with the capacitive impedance component to be compensated, a circuit resonant at the high-frequency voltage.

5. A polarographic apparatus as claimed in claim 4, wherein a resistor is inserted in series with the cell.

6. A polarographic apparatus as claimed in claim 3, wherein means is provided for varying the inductance of the inductive device.

7. A polarographic apparatus as claimed in claim 6, wherein there is provided detector means for detecting the relative phase of the high-frequency current and the high-frequency voltage developed across the series combination of the cell and inductive device, and control means, responsive to the output of the detector means, for varying the inductance of the said inductive device to reduce difference in phase between the aforesaid high-frequency current and high-frequency voltage.