Towards establishing indicative values for metabolites of organophosphate ester contaminants in human urine

In 2015, nine laboratories from Belgium, USA, Canada, China, and Australia participated in an interlaboratory exercise to quantify metabolites of organophosphate ester (OPE) contaminants in pooled human urine. Pooled human urine available as SRM 3673 (Organic contaminants in non-smokers’ urine) was obtained from the U.S. National Institute of Standards and Technology and was analyzed for its content of OPE metabolites. Each participating laboratory received 10 mL sample and used its own validated method and standards to report the concentrations of the OPE metabolites of its choice. Four OPE metabolites were consistently measured by most laboratories and they were the following diesters: bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), diphenyl phosphate (DPHP), bis(2-chloroethyl) phosphate (BCEP), and bis(1-chloro-2-propyl) phosphate (BCIPP). Concentrations of other OPE metabolites in SRM 3673 were also reported but are only considered as informative values since they were measured by three laboratories at most. All laboratories used liquid chromatography with tandem mass spectrometry (LC-MS/MS) with or without solid-phase extraction (SPE). This is the first study to report indicative values for OPE metabolites in a human urine Standard Reference Material. It is expected that these indicative values obtained for these four metabolites will be used as quality control to ensure compatibility of results in biomonitoring studies and by other researchers who validate their own methods for the quantification of OPE metabolites in human urine.