A STUDY OF HPLC SEPARATION AND SPECTROPHOTOMETRIC, POLAROGRAPHIC AND VOLTAMMETRIC DETECTION OF 4-SUBSTITUTED DERIVATIVES OF N-NITROSO-N-METHYLANILINE

Optimised conditions have been found for the separation of N-nitroso-N-methylaniline derivatives substituted in the position 4 (4-R-NMA, where R = - H, - CH3, - OCH3, - Cl, - CN, - OH and - NO2), using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of aqueous 0.01 mol l-1 KH2PO4 with methanol (4 + 6) or acetonitrile (7 + 3), or a mixture of water, methanol, acetonitrile and 80% H3PO4 (200 + 200 +200 +3). Four detection techniques have been investigated: Direct UV photometry, polarography on a hanging mercury drop electrode, anodic voltammetry on a glassy carbon fibre array electrode and indirect anodic voltammetric detection after photolytic denitrosation of the analytes. The UV photometry is the most universal and yields limits of detection around 10(-6) mol l-1. Polarography exhibits the poorest sensitivity (with a limit of detection of ca. 10(-5) mol l-1) but it can be used for selective detection of 4-NO2-NMA. Direct voltammetric detection is selective for the oxidizable derivatives and the limits of detection attained are lower than those obtained by UV photometry (for 4-OH-NMA) or comparable with (for 4-OCH3-NMA). When the analytes are photolytically denitrosated to yield oxidizable derivatives, the voltammetric detection of 4-H-NMA, 4-Cl-NMA, 4-CH3-NMA and 4-NO2-NMA has limits of detection one order of magnitude lower than those obtained UV photometrically.