Comparative Study of the Determination of Parabens in Shampoos by Liquid Chromatography with Amperometric and Coulometric Detection

The simultaneous determination of four para-hydroxybenzoic acid esters (parabens) in shampoos was studied by liquid chromatography (LC) with amperometric (LC-AD) and coulometric (LC-CD) detection The parabens were separated on an ODS C18 reversed column by isocratic elution with a mobile phase based on methanol-0 1 M acetic acid (60.40%. v/v) with 0 02 M NaClO4 at a flow rate of 0 8 mL min(-1) The limit of detection (S/N > 3) for the analytes was in the 15-25 pg (injected mass) range at an applied potential of 1 20 V vs. Ag/AgCl using the LC-AD and in the 2-3 pg range at a potential of 0 790 V vs. Pd using the LC-CD The peak ratio of the internal standard peak (IS 4-hydroxybenzoic acid sec-butyl ester) versus the analyte peak was found to be related to the amount injected from 1 ng to 100ng (r=0 996-0 999) with the LC-AD and from 0 050 ng to MO ng range (r=0 999-1 00))) with the LC-CD The relative standard deviation (RSD, n=10) was comprised between I 8 to 35% by LC-AD ( 5 ng injected) and between 2 0 to 24% by LC-CD (05 ng injected) The determination of our most used parabens in ten different shampoos was successfully realized