Comparative study of different thermospray interfaces with carbamate pesticides: Influence of the ion source geometry

Abstract

Sixteen carbamate pesticides that belong to four chemical classes (oxime-N-methylcarbamates, aryl N-methylcarbamates, N-phenylcarbamates, and methyl esters of substituted carbamic acids) were investigated via three different commercially available thermospray interfaces and ion sources that exh ibit wide differences in source geometry. Comparisons were made between the three interfaces with respect to ion formation and sensitivity of detection. Experimental parameters were standardized to obtain comparable experimental conditions. Very similar mass spectra for most carbamates were obtained that illustrate independence from the geometry of the ion ization and desolvation chambers of the interfaces. These findings are in sharp contrast to several literature reports. However, thermally labile carbamates ga ve unsatisfactory results with regard to spectral compatibility between the interfaces. Such differences were due to thermally assisted hydrolysis reactions that occur in the vaporizer probe prior to ionization and reflect di fferences in the vaporizer designs. The study proves conclusively that comparable spectra can be obtained under thermosprar with different interfaces and mass spectrometers. {J Am Soc Mass Spectrom 1995, 6, 656-667 C urrently thermospray (TSP) has been used extensively as a liquid chromatography-mass spectrometry (LC-MS) interface for the determination of a wide range of chemical classes; for example, pesticides [1][2][3][4][5][6][7] mobile phase [16,17], require adjustments to obtain the necessary limits of detection and reproducibility, Mass spectrometric investigations of carbamate pesticides via different types of TSP interfaces have been reported widely [1][2][3][4][5][6][7][18][19][20][21][22][23][24][25][26]. These studies, however, indicate that solitary protonated molecules and /or molecular ammonium adduct ions are formed by carbamates that provide no structural information. For an unambiguous identification of carbamates in environmental samples, several additional fragment ions are required for proof of presence. Several methods have been reported to increase the number of fragment ions ; for example, use of different ionization modes [1,6], postcolumn addition of adduct reagents [4,19] or increased operating temperatures of the TSP in terface

High‐Performance Liquid Chromatography/Mass Spectrometry Methods in Pesticide Analysis

“…32 Sixteen carbamate pesticides were used in a very interesting comparison, under standardized experimental conditions, among three different TSP interfaces and ion sources to evidence possible differences ion formation and sensitivity of detection. 33 Twelve of the investigated compounds showed no significant differences in their mass spectra, especially at low temperatures. Thermally labile molecules such as asulam, thiodicarb and thiofanox showed significant differences in the mass spectra, mainly due to thermally assisted hydrolysis of the parent compounds in the vaporizer probe, not necessarily reflecting differences in the ion source geometry.…”