Liquid Chromatography Detectors - The Electrochemical Detector > Basic Electrochemical Detector Electronics > Page 94


Courtesy of the Perkin Elmer Corporation


Column: HC-3 C18 (100 mm x 4.6 mm); mobile phase: aqueous solution of 100 nM formic acid , 0.35 nM octane sulphonic acid, 1.0 nM citric acid 0.10 nM EDTA, 5% acetonitrile, 0.25% v/v diethylamine, pH to 3.10 with potassium hydroxide; flow rate 1 ml/min; detection: oxidative amperometric with glassy carbon electrode at 100 mV potential vs. Ag/AgCl electrode.


1. 3,4 dihydroxymendelic acid 200 pg 10. dopamine 200 pg
2. L-dopa 600 pg 11. metanephrine 400 pg
3. vanillymendelic acid 400 pg 12.3,4-dihydroxyphenylacetic acid       200 pg
4. norepinephrin 200 pg 13. N-methyl dopamine 400 pg
5. a-methyl dopa 600 pg 14. tyramine  1 ng
6. 3-methoxy,4-hydroxyphenylglycol     400 pg 15. 5-hydroxyindole-3-acetic acid        200 pg
7. epinephrine 200 pg 16. 3-methoxytyramine 400 pg
8. 3,4-dihydroxybenzylamine 200 pg 17. 5-hydroxytryptamine 200 pg
9. normetanephrin 400 pg 18. homovanillic acid 400 pg


Figure 59. The Separation of Some Catacholamines Monitored by an Electrochemical Detector.

A more serious problem arises from the adsorption of the oxidation or reduction products on the working electrode surface. As a result, the electrode system must be frequently calibrated to ensure accurate quantitative analysis. In addition, the detector must be regularly dissembled and cleaned (usually by a mechanical abrasion). Many attempts have been made to avoid this contamination problem but, although it has been reduced, it has not been completely eliminated (particularly in the amperometric form of operation). Due to potentially low sensing volume the detector is very suitable for use with small bore columns.