Ultra-performance liquid chromatography tandem mass spectrometry for the rapid simultaneous analysis of nine organophosphate esters in milk powder.

Organophosphate esters (OPEs) are common flame retardants that are used in a wide variety of products. These compounds might migrate into and pollute food products. An analytical method involving an improved approach called the "quick, easy, cheap, effective, rugged, and safe" (QuEChERS) method and ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) was developed to simultaneously measure trace levels of nine OPEs in milk powder. Separation of the nine OPEs was optimized on a reversed-phase column within 7 min. The stable isotope tri-n-butyl phosphate-d27 (TBP-d27) was used as an internal standard. This method was validated in terms of its linearity, sensitivity, precision, accuracy and matrix effects. Matrix-matched calibration curves were constructed with 1/x(2) as the weighting factor for all of the target compounds resulting in coefficients of regression lines between 0.9938 and 0.9999. The average accuracy was between 73.5% and 110.2%. Intra- and inter-assay precisions for six replicates ranged from 3.9% to 8.9% or below 11%, respectively. The limits of detection (LODs) were in the range of 0.1-0.25 μg/kg, and the limits of quantification (LOQs) were below 1.5 μg/kg. Significant matrix effects have been observed, but suppression or enhancement of the signal was compensated for by the use of an isotopically labeled internal standard. This validated method was successfully applied to determine the concentrations of the OPEs in milk powder.