A study of HPLC separation and spectrophotometric, polarographic and voltammetric detection of 4-substituted derivatives of N-nitroso-N-methylaniline |
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Authors: | Ji?í Barek Pham Tuan Hai Věra Pacáková Karel ?tulík Ivana ?vagrová and Ji?í Zima |
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Institution: | (1) UNESCO Laboratory of Environmental Electrochemistry, Department of Analytical Chemistry, Charles University, 128 40 Praha 2, Czech Republic |
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Abstract: | 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. |
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