EFFECT OF PH ON THE RETENTION BEHAVIOR OF SOME PRESERVATIVES-ANTIOXIDANTS IN REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

In this paper the dependence of eluent pH on the efficiency of separation in RP-HPLC is described. Preservatives-antioxidants, esters of p-hydroxybenzoic acid (methyl, ethyl, propyl and butyl parabens), sorbic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) and L-ascorbic acid (Vitamine C) were investigated by reversed-phase highperformance liquid chromatography, utilising isocratic elution with UV detection. The mobile phase composition (methanol-water v/v containing 1 % acetic acid), was varied in order to obtain the best separation. For all substances analysed the pH, pKa and the fitted pKa values were calculated in different mixtures of mobile phases using the graphical method of Chariot and Tremillon [1]. The retention factors (k) and the separation factors (alpha) were also calculated.