title: Direct determination of dialkyl phosphates by strong anion-exchange liquid chromatography/atmospheric pressure chemical ionization mass spectrometry using a quadrupole ion trap instrument.
abstract: The direct determination of dialkyl phosphates (DAPs) in water by strong anion-exchange (SAX) liquid chromatography/atmospheric pressure chemical ionization (APCI) mass spectrometry was investigated. The SAX high-performance liquid chromatography (HPLC) column was eluted with methanol/water gradients containing ammonium formate (AF) separating the DAPs which included six dimethyl- and diethyl-substituted phosphates, thiophosphates, and dithiophosphates. The high buffer concentrations required for separation were compatible with -ve APCI, but in +ve APCI the DAPs were unstable giving anomalous ions such as [M+15]+ and [M+29]+. These ions are believed to result from ion molecule reactions with CH3OH2+ in the plasma. DAPs are very stable in -ve APCI being detected as abundant [M-H](-) ions, even with 200 mM AF. At higher AF concentration formate clusters ([M+45](-) and [M+91](-)) were seen. Fragmentation by collision-activated dissociation (CAD) was more efficient for deprotonated ethyl-substituted DAPs which lost ethylene followed by ethanol. APCI instrument detection limits were in the low ng/mL range and the response was highly linear. Isotope dilution quantitation using d10-diethyl dithiophosphate (DEDTP) as an internal standard produced an instrument detection limit of 2 ng DEDTP/mL and method detection limit (MDL) of 9.3 ng/mL with accuracy of 99% (spike concentration, 25 ng/mL). DAP mixtures required storage in cold, dry conditions and alcohol solvents should be avoided because of solvolysis reactions.
authors.affiliation: Sanitation and Radiation Laboratory Branch, California Department of Public Health, 850 Marina Bay Parkway, Richmond, CA 94804, USA. william.draper@cdph.ca.gov
authors.forename: William M
authors.initials: WM
authors.lastname: Draper
authors.forename: Paramjit
authors.initials: P
authors.lastname: Behniwal
authors.forename: Donald
authors.initials: D
authors.lastname: Wijekoon
mesh_terms: D001274:Atmospheric Pressure; D002851:Chromatography, High Pressure Liquid; D007306:Insecticides / Q000032:analysis*; D009943:Organophosphorus Compounds / Q000032:analysis*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation / Q000379:methods*
chemical_list: D007306:Insecticides; D009943:Organophosphorus Compounds