An evaluation of atmospheric pressure ionization techniques for the analysis of N-Methyl carbamate pesticides by liquid chromatography mass spectrometry

Abstract

Atmospheric pressure ionization (API) techniques are evaluated for the mass spectral analysis of N-methyl carbamate pesticides. Atmospheric pressure chemical ionization (APCI) using a heated nebulizer interface provided both protonated molecules and abundant, characteristic fragment ions. With ion spray (ISP; pneumatically assisted electrospray ionization), which utilizes a milder "ion evaporation" process, primarily protonated molecules were obtained, although fragment ions similar to those observed in APCI could be induced by variation of the API orifice voltage. Product ion spectra of ISP-derived protonated molecules, generated by tandem mass spectrometry using collision-induced dissociation, are also presented. The APCI and ISP spectra of the carbamates are compared to those obtained with a thermospray interface and also to their electron ionization and methane CI spectra obtained with a particle beam interface. For all four interfaces, combined liquid chromatography mass spectrometry methods using conventional (4.6 mm i.d.) columns are described for the separation and detection of pesticide mixtures. These methods are applied to the confirmatory analysis of three representative carbamate pesticides, spiked at the 0.1-ppm level in green peppers. For those carbamates amenable to gas chromatography mass spectrometry, comparative results are presented.

A Simple High Performance Liquid Chromatography/Ionspray Tandem Mass Spectrometry Method for the Direct Determination of Paraquat and Diquat in Water

“…Of these, the majority used atmospheric pressure chemical ionization (APCI). 1 Pleasance et al 2 evaluated APCI, ionspray (ISP) (pneumatically assisted electrospray), thermospray (TSP) and particle-beam interfaces for the detection of carbamate pesticides and found that APCI provided superior results. We have successfully used both APCI and ISP for the determination of a variety of pesticides, and have recently reported on the use of ISP for multi-residue analyses.…”

High-performance Liquid Chromatography/Atmospheric Pressure Chemical Ionization Mass Spectrometry with Ionization Polarity Switching for the Determination of Selected Pesticides

“…Doerge and Bajic 7 evaluated the use of APCI-MS for several classes of pesticides, including ASon and CBF, and applied the technique to the analysis of triazine herbicides in water. Pleasance et al 8 evaluated APCI and ESI for the analysis of N-methyl carbamate pesticides (including ALD, ASon, ASox, CBF and 3-OH-C) and compared these techniques with TSP and with particle beam interfacing using electron ionization. Of the 4 techniques APCI had a clear advantage over the other techniques with respect to sensitivity, linearity and range of applicability to all the carbamates studied.…”

Identification of Carbamates by Particle Beam/Mass Spectrometry

“…NCI of carbamates has not been systematically investigated, although there are indications from APCI experiments that NCI is not so well suited for carbamates. 13 In order to investigate the feasibility of CI for carbamate detection with a PB inlet system, we tested 33 analytes (shown in Table 2), under PCI and NCI conditions using methane and ammonia. Special attention was devoted to the inÑuence of ion source temperature and gas pressure on the appearance of spectra.…”