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 electrochemical detection. A mathematical model was used to predict optimal separation 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 performed with a graphite-epoxy working electrode at a potential of 800 mV vs. Ag/AgCl. A palladium metal union was used to decouple the separation field from the electrochemical cell. A compensating pressure was applied to preserve the flat electroosmotic flow profile during analysis. plate numbers up to 150 000 were obtained. The applied detection potential was shown to have an influence on the width of the peaks. Because the noise on the signal increased with the applied separation voltage, an optimum had to be found between detection limits and analysis time. 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 was 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 packing (PLRP-S), the method proved suitable for the analysis of river water samples. When using an internal standard, the average repeatability of the peak area was +/-6% for 14 compounds (n=5). With this preconcentration-method, detection limits lower than 0.1 mu g l(-1) in 100 ml river water sample were obtained.