THE USE OF MOBILE-PHASE ADDITIVES IN THE DETERMINATION OF 55 (POLAR) PESTICIDES BY COLUMN LIQUID-CHROMATOGRAPHY THERMOSPRAY MASS-SPECTROMETRY

The effect of various additives (ammonium acetate, ammonium formate, t riethyl- and tripropylammonium formate and chloroacetonitrile) on the sensitivity and selectivity in liquid chromatography-thermospray-mass spectrometry (positive and negative ion mode) is studied for a group o f 55 pesticides including phenoxy and carboxylic acids, hydroxy-keto-l actones, substituted amides, triazines, (thio)carbamates, phenylureas, substituted phenols, organophosphorus compounds, thiocyanates and ani lines. In the positive ion mode the base peaks correspond to [M + H]and [M + NH4]+ for the majority of the test compounds. Fragmentation i s observed in some isolated cases only. In the negative ion mode proce sses like (dissociative) electron capture and ion-molecule reactions t ake place. Fragment ions such as [M - H - CONCH3]- for the carbamates, [M - C3H6O]- for the hydroxy-keto-lactones and [M - H]- for the chlor inated phenoxy acids are observed. Depending on the additive used, add uct ions such as [M + CH3COO]-, [M + HCOO]- and [M + CI]- are formed. Adducts with fragment ions are also observed quite often. The use of t riethylammonium formate and tripropylammonium formate instead of ammon ium formate increases the sensitivity and selectivity of the method in the NI mode, because their high proton affinity enhances deprotonatio n.