The 2-substituted-4, 6-di-(alkylamino)-l,3,5-triazines (s-triazines) are well known pesticides. With the dramatic increase in usage patterns of pesticides, an urgent need has arisen to develop analytical techniques to assist in identification of such compounds. A comprehensive understanding of the major fragmentations of these molecules, after ionization, could aid in this task. The use of conventional ionization techniques such as electron impact or chemical ionization is limited because 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 thermolabde and low volatility compounds such as environmental compounds. Among these techniques, the desorption ionization technique called "plasma desorption" (PD) leads to more informative m a s spectra than those obtained with other ionization techniques. A systematic investigation of ion formation and decomposition processes of three families of 2-X substituted-s-triazines (X=Cl, SCH3 and OCH,) 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 PD conditions is investigated in detail. Specific molecular ions (adduct ion, substitution ions . . .) allow the differentiation of each family, while characteristic fragment ions lead to the identification of the 1,3,5-triazine ring and/or of its substituents. The fragmentation processes are obtained 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 compounds under PD conditions. The experimental results are supported by semi-empirical molecular orbital calculations. Finally, the proton affinity of Ametryn (2-methylthio-4-(isopropylamino)-6-(ethylamino)-s-triazine) was determined to be close to that of histidine i.e. 970 k.J/mol.The plasma desorption ionization technique is chosen to analyse three families of s-triazines: (i) 2-chloro-4,6-diamino-1,3,5-triazines with different R,, R, substituents on the amino functions i.e. R, = R, = ethyl (Simazine) , R1 = R2 = isopropyl (Propazine) , R, = isopropyl, Rz =ethyl (Atrazine); (ii) 2-methylthiod, 6-diamino-173,5-triazines substituted with R, = R2 = ethyl (Simetryn), R, = Rz = isopropyl (Prometryn), R, = isopropyl, R2 = ethyl (Ametryn), R, = tert-butyl, R2 = ethyl (Terbutryn) and (iii) 2-methoxy-4, 6-diamino-l,3,5triazine substituted with an isopropyl group (R,=R,) on each amino function (Prometon) (Scheme 1). Plasma desorption mass spectrometry (PDMS), first introduced by Macfarlane and Torgerson,' uses the high-energy fragments emitted from the spontaneous fission of 252Cf to desorb and ionize intact large or non-volatile molecules for mass analysis. Recently, this technique was shown to be well suited for analysis of small mole...

Several studies concerning the analysis and quantification of biological and pharmaceutical compounds have been effected during the past 20-30 years using different techniques of desorption-ionization. In most cases, however, the authors have not been interested in the mass spectrometric fragmentation mechanisms of these products. Plasma desorption mass spectrometry (PDMS) is a powerful technique for analysing, without matrix interferences, solid biological and pharmaceutical compounds. In this work, we use PDMS in order to study the influence of the amine (amide) function on the fragmentation processes of nitrogen-containing compounds. For this work, quaternary ammonium salts, trisubstituted amines, disubstituted amines and a compound with an amide function were chosen. Classical PD mass spectra, accurate mass measurements, transitions in the field free region (FFR), labelled compound spectra and thermodynamical data are reported for the structural study of these compounds. Our results allow us to propose fragmentation rules for positively charged polyfunctional biological nitrogen compounds. These rules relate to a class of structurally informative decomposition reactions that can be applied to the determination and of identification of structural unknowns.In an attempt to apply modern mass spectrometric techniques to direct analysis of biological and pharmaceutical compounds, plasma desorption-ionization was employed. Plasma desorption mass spectrometry, introduced by Macfarlane and Torgerson,' uses energetic fission fragments from the decay of 252Cf to volatilize and ionize a solid sample. This technique was one of the first particle bombardment techniques successfully applied for the formation of gas-phase ions of nonvolatile and thermally labile biomolecules. The PDMS technique has been extensively used for measuring the molecular weights of biopolymers in the mass range 103-3 x lo4 u. Recently, this technique was demonstrated to be very useful for the analysis of small molecules and for obtaining structural information from small and large molecules.' This paper describes the decomposition mechanisms of positively charged ions from biological and pharmaceutical compounds containing several functional groups including, at least, one amine or one amide function and shows that the fragmentation is chargeinduced or charge-remote depending on the substituents of the ionized nitrogen atom. The mechanisms and some applications of charge-remote fragmentations have been studied by Gross.3 We have applied these mechanisms to nitrogen-containing organic compounds of biological and pharmaceutical interest.The compounds studied and presented in Table 1 are: quaternary ammonium salts, namely L-carnitine inner salt l a , L-carnitine hydrochloride l b and thiamine hydrochloride 2; trisubstituted amines, namely chlorpromazine hydrochloride 3, thioridazine hydrochloride 4 and riboflavin 5; disubstituted amines, such as niflumic acid 6; amphetamines, namely fenproporex 7, fenfluramine 8 and methylamphetamine 9; and an amide,...

Electron impact (EI) using ionizing electrons of different kinetic energies, ammonia and methane positive chemical ionization (PCI) and plasma desorption (PD) mass spectrometry were used for the analysis of aryl pesticides of the carbamate and phenylurea families. Under PD conditions, competitive formation and decomposition of M+. and MH+ ions was observed. It is shown that PD spectra give more information than do EI or PCI spectra, confirming PD as a method of choice for the analysis of small polyfunctional molecules. Rules are given for the identification of these families of pesticides. A thermochemical desorption ionization model defines the conditions required for the observation of both M+. and MH+ ions. © 1997 John Wiley & Sons, Ltd.