A STUDY OF HPLC SEPARATION AND SPECTROPHOTOMETRIC AND VOLTAMMETRIC DETECTION OF 4'-SUBSTITUTED DERIVATIVES OF 3-CARBOXY-4-HYDROXY-6-ACETYLAMINOAZOBENZENE

Optimised conditions have been found for the separation of 3-carboxy-4 -hydroxy-6-acetylaminoazobenzene derivatives substituted in the positi on 4'(4'-R-CHAAB, where R = -H, -CH3, -OCH3, -Cl, -COCH3, -NO2 and -NH COCH3) using reversed phase HPLC with a C18 chemically bonded stationa ry phase. Suitable mobile phases are mixtures of 0.01 mol/L NaH2PO4 at pH 4 with methanol (1 + 1), 0.01 mol/L NaH2PO4 at pH 2 with acetonitr ile (1 + 1) or 1% aqueous acetic acid with methanol (4 + 6). UV photom etry is the most universal detection technique and yields limits of de tection around 10(-6) mol/L. Direct anodic voltammetry on a glassy car bon fibre array detector yields lower limits of detection for -COCH3 d erivatives and higher limits of detection for -NO2 and -NHCOCH3 deriva tives. When the analytes are chemically reduced using zinc powder in a cetic acid, the voltammetric detection has limits of detection one ord er of magnitude lower than those obtained UV photometrically.