Barceló D, Durand G, Vreeken R J, De Jong G J, Lingeman H, Brinkman U A
Environmental Chemistry Department, CID-CSIC, Barcelona, Spain.
J Chromatogr. 1991 Aug 16;553(1-2):311-28. doi: 10.1016/s0021-9673(01)88502-2.
The influence of different eluents in positive and negative ion mode thermospray liquid chromatography-mass spectrometry was studied with several groups of pesticides, including carbamates, chlorotriazines, phenylureas, phenoxy acids and organophosphorus and quaternary ammonium compounds, and the corresponding degradation products. Using the positive ion mode in combination with reversed-phase eluents the base peaks generally corresponded either to [M + H]+ for the chlorotriazines and their hydroxy metabolites or to [M + NH4]+ for the carbamates, the phenylureas, the organophosphorus pesticides and their oxygen analogues. In the negative ion mode different processes such as (dissociative) electron-capture and anion attachment mechanisms occurred. Fragment ions such as [M - CONHCH3]- for the carbamates, [M - H]- for the chlorotriazines, phenylureas and chlorinated phenoxy acids and [M].-, [M - R]- (R being a methyl or ethyl group) for organophosphorus pesticides were usually formed. Depending on the eluent additive used (ammonium acetate, ammonium formate and/or chloroacetonitrile), three different adduct ions were formed: [M + CH3COO]-, [M + HCOO]- and [M + Cl]-. Normal-phase eluents with cyclohexane, n-hexane and/or dichloromethane provided more structural information and enhanced the response of several compounds. The positive ion mode was useful for the detection of chlorinated phenoxy acids and chlorophenols which could not be detected in the positive ion mode using reversed-phase systems. The base peaks generally corresponded to [M].+, [M + H]+ or [M - Cl]+. For the characterization of difenzoquat, a quaternary ammonium pesticide of which trace level analysis is troublesome, a post-column ion-pair extraction system was used. An aqueous mobile phase with a sulphonate-type counter ion was applied and an extraction solvent containing cyclohexane-dichloromethane-n-butanol (45:45:10) was used in thermospray liquid chromatography-mass spectrometry. Illustrative examples of the determination of residue levels of pesticides in soil matrices are shown.
采用几组农药，包括氨基甲酸酯类、氯代三嗪类、苯基脲类、苯氧酸类、有机磷和季铵化合物及其相应的降解产物，研究了正离子和负离子模式热喷雾液相色谱 - 质谱联用中不同洗脱剂的影响。在正离子模式下结合反相洗脱剂，氯代三嗪类及其羟基代谢物的基峰通常对应于[M + H]+，而氨基甲酸酯类、苯基脲类、有机磷农药及其氧类似物的基峰对应于[M + NH4]+。在负离子模式下，会发生不同的过程，如（解离）电子捕获和阴离子附着机制。通常会形成碎片离子，如氨基甲酸酯类的[M - CONHCH3]-、氯代三嗪类、苯基脲类和氯化苯氧酸类的[M - H]-，以及有机磷农药的[M].-、[M - R]-（R为甲基或乙基）。根据所使用的洗脱剂添加剂（醋酸铵、甲酸铵和/或氯乙腈），会形成三种不同的加合离子：[M + CH3COO]-、[M + HCOO]-和[M + Cl]-。使用环己烷、正己烷和/或二氯甲烷的正相洗脱剂可提供更多结构信息，并增强几种化合物的响应。正离子模式对于检测在反相系统正离子模式下无法检测到的氯化苯氧酸类和氯酚类很有用。基峰通常对应于[M].+、[M + H]+或[M - Cl]+。对于难以进行痕量分析的季铵农药敌草快的表征，使用了柱后离子对萃取系统。在热喷雾液相色谱 - 质谱联用中，采用含有磺酸盐型抗衡离子的水性流动相，并使用含有环己烷 - 二氯甲烷 - 正丁醇（45:45:10）的萃取溶剂。展示了土壤基质中农药残留水平测定的示例。
