Oyster is a common indicator organism of environment pollution. A method was built to simultaneously determine ten common commercial organophosphate ester flame retardants in oysters. After the careful optimization of conditions, the organophosphate esters (OPEs) in oyster sample were extracted with hexane assisted by ultrasound, purified with NH2 solid-phase extraction column, eluted with the mixture solution of dichloromethane and ethyl acetate at the ratio of 1:1 (v/v), and finally detected by gas chromatography coupled with tandem triple quadrupole mass spectrometry (GC–MS/MS). All the ten compounds in the concentrations ranging from 0.5 ng·mL-1 to 100 ng·mL-1 showed good linearity with their R2 higher than 0.9991. The limits of detection and limits of quantification for the organophosphate esters were from 0.03 ng·g-1 to 0.47 ng·g-1 (dry weight) and from 0.1 ng·g-1 to 1.56 ng·g-1 (dry weight), respectively. At the three spiking levels with five replicates, recoveries of organophosphate esters ranged from 82% to 108% with the relative standard deviation ranging from 0.9% to 6.4%. In the samples collected from mariculture farms, nine OPE compounds were detected in oysters with the concentration ranging from 6.52 ng·g-1 to 22 ng·g-1 (dry weight). It indicated the method was suitable for OPEs determination in oysters.

0.5 g of oyster sample was weighed into a 50 mL centrifuge tube and then equilibrated for 30 min followed by the addition of 50 μL mixture of internal standards (1 μg·mL-1).

After the addition of 3 g of anhydrous sodium sulphate and 10 mL of hexane, the mixture in the centrifuge tube was vortexed for 2 min (IKA MS3 Basic, IKA Works GmbH & Co, Germany), ultrasonically treated for 30 min (KQ-250E, Kun Shan Ultrasonic Instruments Co., Ltd, China), and then centrifuged for 10 min at 5500 rpm at 4℃ (Anke DL-6000B, Shanghai Anting Scientific Instruments Factory, China). The supernatant was transferred to another 50 mL tube. The extraction process was repeated and the supernatant of the two extractions was then applied to the NH2 cartridge which has been preconditioned with 3 mL of DCM/EA (1:1, v/v) and 3 mL of hexane. After rinsing with 3 mL of hexane, the target compounds were eluted with 6 mL of DCM/EA (1:1, v/v). The eluent was dried under a gentle nitrogen flow and reconstituted in 1 mL of EA.