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, whe re R = - H, - CH3, - OCH3, - Cl, - CN, - OH and - NO2), using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mo bile 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, acet onitrile and 80% H3PO4 (200 + 200 +200 +3). Four detection techniques have been investigated: Direct UV photometry, polarography on a hangin g mercury drop electrode, anodic voltammetry on a glassy carbon fibre array electrode and indirect anodic voltammetric detection after photo lytic denitrosation of the analytes. The UV photometry is the most uni versal and yields limits of detection around 10(-6) mol l-1. Polarogra phy 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-N MA. Direct voltammetric detection is selective for the oxidizable deri vatives and the limits of detection attained are lower than those obta ined by UV photometry (for 4-OH-NMA) or comparable with (for 4-OCH3-NM A). When the analytes are photolytically denitrosated to yield oxidiza ble derivatives, the voltammetric detection of 4-H-NMA, 4-Cl-NMA, 4-CH 3-NMA and 4-NO2-NMA has limits of detection one order of magnitude low er than those obtained UV photometrically.