Method of operating a self cleaning electrochemical detector

• US 4,566,949 A
• Filed: 10/11/1984
• Issued: 01/28/1986
• Est. Priority Date: 10/19/1983
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Berger, Terry A.
• Primary Examiner(s): Kaplan, G. L.
• Application Number:
  US06/659,792
• Time in Patent Office: 474 Days
• Field of Search: 204/1 T, 204/402, 204/406, 204/409, 204/411, 204/412, 204/70, 436/161, 73/61.1 C, 324/425
• US Class Current: 205/794.5
• CPC Class Codes: G01N 27/38 Cleaning of electrodes
• CPC Class Codes: G01N 30/64 Electrical detectors

Abstract

An improved electrochemical cell and detector which is especially suited for analysis of rapidly changing flowing streams such as found in high performance liquid chromatography is disclosed. A uniquely designed jet made of microbore drawn capillary tubing permits the construction of a cell for very low flow rates that still retains true wall-jet hydrodynamics. The invention prevents changes in cell response in time by periodically cleaning a working electrode in a novel way. Cleaning and detection are both accomplished on a time scale much shorter than the fastest liquid chromatograph peaks by means of a unique three electrode cell design utilizing a small diameter, low capacitance, metal working electrode situated close to a reference electrode. Cleaning is accomplished by means of a nonsquare wave periodic waveform which is effective in cleaning a wide variety of contaminants through the oxidation and reduction of the working electrode and/or solvent prior to application of one or more working potentials while providing a stable, reproducible detector. The detector thus provides improvements in both sensitivity and bandwidth over the prior art.

Claims

1. A method of detecting the concentration of electrochemical species in a fluid with an electrochemical cell with a working electrode comprising:

oxidizing the working electrode for a period less than or equal to 200 milliseconds;

reducing the working electrode for a period less than or equal to 200 milliseconds;

applying a working potential to the working electrode for a period less than or equal to 800 milliseconds; and

measuring a current produced by electrochemical reactions on the working electrode at the working potential for integer multiples of a main power line period.

2. A method as in claim 1 further comprising:

flowing the fluid through the electrochemical cell.

3. A method as in claim 1 further comprising applying a plurality of working potentials to the working electrode for a plurality of periods each less than or equal to 800 milliseconds.

4. A method of detecting the concentration of electrochemical species in a fluid with an electrochemical cell with a working electrode comprising a metal, said method comprising:

oxidizing the working electrode for a first period less than or equal to 200 milliseconds so that the surface area of the working electrode increases;

reducing the working electrode for a second period less than or equal to 200 milliseconds so that the surface area of the working electrode decreases;

applying a working potential to the working electrode for a third period less than or equal to 800 milliseconds, and

measuring a current produced by electrochemical reactions on the working electrode at the working potential.

5. A method as in claim 4 further comprising applying a plurality of working potentials to the working electrode for a plurality of periods each less than or equal to 800 milliseconds.

6. A method as in claim 4 wherein the first and second periods are applied in reverse order.

7. A method as in claim 4 further comprising flowing the fluid through the electrochemical cell.

8. A method as in claim 4 comprising:

further oxidizing the fluid during the first period to produce oxygen bubbles on the working electrode; and

further reducing the fluid during the second period to produce hydrogen bubbles on the working electrode.

9. A method as in claim 8 further comprising applying a plurality of working potentials to the working electrode for a plurality of periods each less than or equal to 800 milliseconds.

10. A method as in claim 8 wherein the first and second periods are applied in reverse order.

11. A method as in claim 8 further comprising flowing the fluid through the electrochemical cell.