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.
