Simultaneous determination of phenylenediamine isomers and dihydroxybenzene isomers in hair dyes by capillary zone electrophoresis coupled with amperometric detection

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE-AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CZE-AD were investigated. Under the optimum conditions the five analytes could be perfectly separated in 0.30 mol L-1 borate-0.40 mol L-1 phosphate buffer (pH 5.8) within 15 min. A 300 mu m diameter platinum electrode had good responses at + 0.85 V (versus SCE) for the five analytes. Their linear ranges were from 1.0 x 10(-6) to 1.0 x 10(-4) mol L-1 and the detection limits were as low as 10 (-7) mol L-1 (S/N= 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0-108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples.