Liquid chromatography-electrospray-tandem mass spectrometry method for determination of organophosphate diesters in biotic samples including Great Lakes herring gull plasma.

Environmentally relevant organophosphate (OP) triester flame retardants are known to degrade to OP diester phosphoric acids. In this study, a quantitatively sensitive method was developed for OP diesters in biological samples of varying complexity, bovine serum, chicken egg homogenate and pork liver. Fortified with 1ng or 10ng each of the six OP diester and six OP triester standards, samples were extracted by accelerated solvent extraction that completely separated OP diesters and triesters. OP diester fractions were cleaned up using weak anion exchange solid phase extraction and eluted with high ionic strength ammonium acetate buffer. Optimal analysis of chlorinated OP diesters was via decamethonium hydroxide dicationic reagent derivatization and by LC-ESI(+)-MS/MS, and for all non-chlorinated OP diesters by non-derivatized LC-ESI(-)-MS/MS. Except for derivatization LC-ESI(+)-MS/MS analysis of liver, at the 10ng spiking level for the three matrices, recovery efficiencies, matrix effects and method limits of quantification (MLOQs) of OP diesters ranged from 55-116%, 92-119%, and 0.02-0.31ng/g wet weight (ww) respectively. Plasma samples of n=6 herring gulls (2010, Chantry Is., Laurentian Great Lakes) contained triphenyl phosphate and tris(1-3-dichloro-2-propyl) phosphate ranging from 1.3 to 4.0ng/g ww and <MLOQ to 0.41ng/g ww respectively. The OP diesters bis(1,3-dichloro-2-propyl) phosphate, bis-(2-butoxyethyl) phosphate and di(2-ethylhexyl) phosphate ranged from 0.7 to 3.5ng/g ww, 0.08 to 29.4ng/g ww and <MLOQ to 0.18ng/g ww respectively, and thus OP triester to diester metabolism occurs in exposed wild herring gulls.