Optimised conditions have been found for the separation of 3-carboxy-4-hydroxy-6-acetylaminoazobenzene derivatives substituted in the position 4′ (4′-R-CHAAB, where R = -H, -CH3, -OCH3, -Cl, -COCH3, -NO2 and -NHCOCH3) using reversed phase HPLC with a C18 chemically bonded stationary 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 acetonitrile (1 + 1) or 1% aqueous acetic acid with methanol (4 + 6). UV photometry is the most universal detection technique and yields limits of detection around 10-6 mol/L. Direct anodic voltammetry on a glassy carbon fibre array detector yields lower limits of detection for -COCH3 derivatives and higher limits of detection for -NO2 and -NHCOCH3 derivatives. When the analytes are chemically reduced using zinc powder in acetic acid, the voltammetric detection has limits of detection one order of magnitude lower than those obtained UV photometrically.
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