Screening of agrochemicals in foodstuffs using low-temperature plasma (LTP) ambient ionization mass spectrometry

Abstract

Low-temperature plasma (LTP) permits direct ambient ionization and mass analysis of samples in their native environment with minimal or no prior preparation. LTP utilizes dielectric barrier discharges (DBDs) to create a low power plasma which is guided by gas flow onto the sample from which analytes are desorbed and ionized. In this study, the potential of LTP-MS for the detection of pesticide residues in food is demonstrated. Thirteen multi-class agricultural chemicals were studied (ametryn, amitraz, atrazine, buprofezin, DEET, diphenylamine, ethoxyquin, imazalil, isofenphos-methyl, isoproturon, malathion, parathion-ethyl and terbuthylazine). To evaluate the potential of the proposed approach, LTP-MS experiments were performed directly on fruit peels as well as on fruit/vegetable extracts. Most of the agrochemicals examined displayed remarkable sensitivity in the positive ion mode, giving limits of detection (LOD) for the direct measurement in the low picogram range. Tandem mass spectrometry (MS/MS) was used to confirm identification of selected pesticides by using for these experiments spiked fruit/vegetable extracts (QuEChERS, a standard sample treatment protocol) at levels as low as 1 pg, absolute, for some of the analytes. Comparisons of the data obtained by direct LTP-MS were made with the slower but more accurate conventional LC-MS/MS procedure. Herbicides spiked in aqueous solutions were detectable at LODs as low as 0.5 microg L(-1) without the need for any sample preparation. The results demonstrate that ambient LTP-MS can be applied for the detection and confirmation of traces of agrochemicals in actual market-purchased produce and in natural water samples. Quantitative analysis was also performed in a few selected cases and displayed a relatively high degree of linearity over four orders of magnitude.

Operation modes of the helium dielectric barrier discharge for soft ionization

“…DBDs are used for the detection of atomic analytes because they are simple and inexpensive and because of their potential for portable detection in real time. Attention has been focused on the application of these plasmas as ambient desorption-ionization (ADI) sources, for the detection of molecular species, capable of producing rapid analytical results with little or no sample preparation [1][2][3][4][5][6][7].…”

Pesticide analysis at ppt concentration levels: coupling nano-liquid chromatography with dielectric barrier discharge ionization-mass spectrometry

“…More recently, different plasma-based ionization sources, including the low-temperature plasma (LTP) source, have been developed and employed for pesticide analysis, where they can deliver very high sensitivity [10][11][12]. Most of these sources are based on a dielectric barrier discharge, and they are gaining attention in the mass spectrometric community [13].…”

The Effects of Added Hydrogen on Noble Gas Discharges Used as Ambient Desorption/Ionization Sources for Mass Spectrometry

“…The chemicals used in this study were chosen to match previous studies [9,10,20,21] done with pure helium and hydrogen-doped helium. They included caffeine (Sigma Aldrich, Steinheim, Germany), diphenylamine (Brigham Young University chemical surplus, source unknown), anthracene (Spectrum Chemical Mfg.…”