Trace level determination of selected organophosphorus pesticides and their degradation products in environmental air samples by liquid chromatography-positive ion electrospray tandem mass spectrometry

Abstract

This paper describes a new analytical method for determination of organophosphorus pesticides (OPs) along with their degradation products involving liquid chromatography (LC) positive ion electrospray (ESI+) tandem mass spectrometry (MS-MS) with selective reaction monitoring (SRM). Chromatography was performed on a Gemini C6-Phenyl (150 mmx2.0 mm, 3 microm) with a gradient elution using water-methanol with 0.1% formic acid, 2 mM ammonium acetate mobile phase at a flow rate of 0.2 mL min(-1). The LC separation and MS/MS operating conditions were optimized with a total analysis time less than 40 minutes. Method detection limits of 0.1-5 microg L(-1) for selected organophosphorus pesticides (OP), OP oxon degradation products, and other degradation products: 3,5,6-trichloro-2-pyridinol (TCP); 2-isopropyl-6-methyl-4-pyrimidol (IMP); and diethyl phosphate (DEP). Some OPs such as fenchlorphos are less sensitive (MDL 30 microg L(-1)). Calibration curves were linear with coefficients of correlation better than 0.995. A three-point identification approach was adopted with area from first selective reaction monitoring (SRM) transition used for quantitative analysis, while a second SRM transition along with the ratio of areas obtained from the first to second transition are used for confirmation with sample tolerance established by the relative standard deviation of the ratio obtained from standards. This new method permitted the first known detection of OP oxon degradation products including chlorpyrifos oxon at Bratt's Lake, SK and diazinon oxon and malathion oxon at Abbotsford, BC in atmospheric samples. Atmospheric detection limits typically ranged from 0.2-10 pg m(-3).

Chemical Analysis of Pesticides Using GC/MS, GC/MS/MS, and LC/MS/MS

“…However, a significant number of OPs which are widely used give significantly lower detection limits with LC/MS/MS (Table 1). In addition GC/MS methods suffer from poor chromatographic performance, low sensitivity, and required derivatization for OP transformation products, whereas LC/MS/MS can be used to simultaneous analyze the OP transformation products including OP oxons with detection limits of 0.06-0.38 µg/L (Raina and Sun, 2008) and OP sulfones and sulfoxides (Chung and Chan, 2010;Jansson et al, 2004;Hiemstra et al, 2007;Economou et al, 2009). For some pyrethroids GC/EI-MS has approximately 100 times higher detection limits than LC/MS/MS (Alder et al, 2006) while for many they are comparable (Yoshida et al, 2009).…”

“…For OPs ESI+ is superior and generally [M+H]+ is observed as the parent ion even in mobile phases only containing methanol. The presence of both ammonium and formic acid was shown to give optimal sensitivity or OPs, OP oxons, and other OP transformation products (Raina and Sun, 2008). For OP sulfone and sulfoxide transformation products sodium adducts can form in mobile phases containing only methanol or methanol with formic acid.…”

“…As a general rule the choice of positive or negative mode depends upon polarity and acidity of analytes and sample matrix impacts. In general, ESI-is more sensitive for phenoxyacid herbicides and their transformation products (Raina and Etter, 2010;Koppen et al, 1998;Dijkman et al, 2001) and chloroacetanilide transformation products; ESI+ for sulfonylureas, phenylureas, N-methylcarbamates, organophosphorus pesticides (Cessna et al, 2006;Degenhardt et al, 2010;Hernandez et al, 2006;Steen et al, 1999;Raina and Sun, 2008); APCI+ for triazines (Dagnac et al, 2005;Jeannot et al, 2000); and APCI+ or ESI+ for chloroacetanilides (Dagnac et al, 2005;Ferrer et al, 2007;Banerjee et al, 2009 …”

“…However these chloro and nitrophenols have also been analyzed successfully by APCI (Silgoner et al, 1997). OP degradation products including 3,5,6-trichloro-2-pyridinol, diethyl phosphate, 2-isopropyl-6-methyl-4-pyrimidinol, malathion monocarboxylic acid, and OPoxons (Raina and Sun, 2008) as well as OP sulfones and sulfoxides (Jansson et al, 2004;Chung andChang, 2010, Hiemstra et al, 2007;Economou et al, 2009) are more sensitive with LC-ESI + /MS/MS and some OPs observe a drastic loss in sensitivity with an APCI source at high flow rates (Asperger et al, 2001). Degradation products of triazines and phenylureas have been done by LC-APCI + /MS/MS but for triazines lower MDLs can be achieved with GC-EI/MS/MS (Dagnac et al, 2005;Goncalves et al, 2006).…”

“…Table 3 shows the vast majority of LC/MS/MS methods utilize C18 columns in order to achieve the desired selectivity for the separation. A few separations have taken advantage of different selectivity from ZIC-pHILIC, C6-phenyl, C8, or C12 (Raina and Sun, 2008;Degenhardt et al, 2010;Crnogorac et al, 2007;Blasco and Pico, 2004). In general methods provide the necessary resolution for compounds with the same SRM transitions.…”