DETERMINATION OF PARAQUAT AND DIQUAT BY LIQUID-CHROMATOGRAPHY THERMOSPRAY MASS-SPECTROMETRY

Thermospray liquid chromatography-mass spectrometry can be used for identifying and determining both paraquat (C12H14N22+) and diquat (C12H12N22+). Reversed-phase liquid chromatography was performed using a 15-cm Shim-pack CLC-ODS column, with methanol-water (80:20) + 0.1 M ammonium acetate (adjusted to pH 5 with trifluoroacetic acid) as buffers, at a flow-rate of 1.0 ml/min. The mass spectral sensitivity was best when the temperatures of the vaporizer, block and tip heater of the ion source block were set at 160, 310 and 320-degrees-C, respectively. When thermospray ionization was used, ions of m/z 186 and 183 were obtained as base peaks for paraquat and diquat, respectively. Detection limits by selected ion monitoring were of the order of 20 ng (S/N = 3.5). The mass spectra are influenced by temperature and therefore, precise temperature control is essential.