DETERMINATION OF CHLOROPHENOLS BY MICELLAR ELECTROKINETIC CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

A method has been developed for the determination of chlorophenols by micellar electrokinetic chromatography (MEKC) coupled with electrochem ical detection. A mathematical model was used to predict optimal separ ation conditions; 17 of the 20 compounds of interest (19 chlorophenols and phenol) were baseline-separated in a 50 mmol l(-1) AGES buffer at pH 6.1, with 22 mmol l(-1) sodium dodecylsulfate. Detection was perfo rmed with a graphite-epoxy working electrode at a potential of 800 mV vs. Ag/AgCl. A palladium metal union was used to decouple the separati on field from the electrochemical cell. A compensating pressure was ap plied to preserve the flat electroosmotic flow profile during analysis . plate numbers up to 150 000 were obtained. The applied detection pot ential was shown to have an influence on the width of the peaks. Becau se the noise on the signal increased with the applied separation volta ge, an optimum had to be found between detection limits and analysis t ime. Detection limits were in the order of 10 mu g l(-1), one to three orders of magnitude lower than with UV detection. The repeatability w as typically +/-0.9% for the (electroosmotic flow corrected) mobility and +/-4% for the peak area (n=7). Combined with off-line solid-phase extraction on a column with a polystyrene-divinylbenzene copolymer pac king (PLRP-S), the method proved suitable for the analysis of river wa ter samples. When using an internal standard, the average repeatabilit y of the peak area was +/-6% for 14 compounds (n=5). With this preconc entration-method, detection limits lower than 0.1 mu g l(-1) in 100 ml river water sample were obtained.