USE OF PLASMA DESORPTION MASS-SPECTROMETRY FOR PESTICIDE ANALYSIS - THE S-ALKYLAMINOTRIAZINES

The 2-substituted-4, 6 di-(alkylamino)-1,3,5-triazines (s-triazines) a re well known pesticides. With the dramatic increase in usage patterns of pesticides, an urgent need has arisen to develop analytical techni ques to assist in identification of such compounds. A comprehensive un derstanding of the major fragmentations of these molecules, after ioni zation, could aid in this task. The use of conventional ionization tec hniques such as electron impact or chemical ionization is limited beca use of the relatively low volatility of these compounds, or because of thermal limitations. Recently, there have been promising developments in desorption ionizaion techniques for analysis of thermolabile and l ow volatility compounds such as environmental compounds. Among these t echniques, the desorption ionization technique called 'plasma desorpti on'' (PD) leads to more informative mass spectra than those obtained w ith other ionization techniques. A systematic investigation of ion for mation and decomposition processes of three families of 2-X substitute d-s-triazines (X=Cl, SCH3 and OCH3) under PD conditions is presented. Eight pesticides were studied in this work. The influence of the X and alkyl substituents on the fragmentation processes under FD conditions is investigated in detail. Specific molecular ions (adduct ion, subst itution ions ...) allow the differentiation of each family, while char acteristic fragment ions lead to the identification of the 1,3,5-triaz ine ring and/or of its substituents. The fragmentation processes are o btained by combining nominal masses of ions determined in positive-ion mass spectra and metastable transitions of low internal energy ions, This study is extended to analysis of s-triazine mixtures. The results obtained lead to the establishment of a desorption order of these com pounds under PD conditions. The experimental results are supported by semi-empirical molecular orbital calculations. Finally, the proton aff inity of Ametryn thio-4-(isopropylamino)-6-(ethylamino)-s-triazine) wa s determined to be close to that of histidine i.e, 970 kJ/mol.