Determination of 15 Organophosphate Ester Flame Retardants in Soils and Sediments by Gas Chromatography-Mass Spectrometry with Accelerated Solvent Extraction

Organophosphate ester flame retardants have widely existed in the environment for several years, and long-term exposure will have an impact on human health. Therefore, it is necessary to investigate their pollution level in the environment, and a multi-component, simultaneous and accurate analysis method is the basis of research. The analytical methods still need to be improved in terms of the types of compounds and extraction efficiency. As a result, it is necessary to establish a rapid and accurate method for analyzing multiple types of organophosphate ester flame retardants in soil and sediment.

To establish a rapid and accurate method for the analysis of 15 organophosphate ester flame retardants in soil and sediment.

The pretreatment was optimized, including the preparation methods for soil and sediment samples, the extraction solvent and extraction temperature for accelerated solvent extraction (ASE), and various parameters of the purification process. The analysis procedure was as follows: Weigh 10.0g (accurate to 0.01g) of the fresh sample, add an appropriate amount of diatomite, stir evenly, and grind into particles. The samples were transferred to the ASE extraction tank, and a quantity of surrogates (tri-butyl phosphate-D₂₇ and tri-phenyl phosphate-D₁₅) were added. The samples were extracted by ASE with n-hexane/acetone (1∶1, V/V). After concentrating the extract to a volume of 2-3mL, the extracts were removed from the water by adding anhydrous sulfuric acid. The purification was carried out using a GCB-NH₂ SPE column. The target compounds were eluted with 10mL eluent solution (5% toluene n-hexane/acetone, 8∶2, V/V). The eluents were concentrated and fixed to 1.0mL by n-hexane. The final extracts were analyzed by gas chromatography-mass spectrometry, and the target compounds were quantified by internal standard calibration curve method.

The extraction efficiency of dry and fresh samples was compared. It was found that the fresh samples with a small amount of water were extracted directly with the solvent, making the organic solvent more able to better contact with the sample particles, and significantly improving the extraction efficiency of the target compound. For example, the recovery of TCEP was greater than 90%, which was significantly higher than previous studies of 86%³³ and 31.2%-48.9%³⁹.　　The sample was extracted twice using a solvent of n-hexane/acetone (1∶1, V/V) at 80℃ by accelerated solvent extraction (ASE) to obtain the best extraction effect. The solid phase extraction (SPE) columns of GCB combined NH₂ were used to purify samples. Large amounts of pigments and other small molecule substances such as acids, lipids, alcohols, sugars, steroids were removed by this method. n-hexane/acetone (8∶2, V/V) with 5% toluene was selected as the elution solvent. The addition of 5% toluene could enhance the elution TCP from GCB solid-phase extraction column. The solid phase extraction recoveries of the target compound under this condition were between 64.7% and 123.6%.　　The linear range of the method was 10-500ng/mL except for TBEP, which ranged from 20 to 500ng/mL. The linear correlation coefficients of the standard curves of all target compounds were greater than 0.9962. The precision experiments results showed that the average recoveries of five spiked levels (2.0, 5.0, 10.0, 50.0, and 500.0ng/g) ranged from 72.6% to 112.9%, and the RSD ranged from 1.6% to 25.3%. The recoveries of surrogates ranged from 84.7% to 114.3%. The method detection limits of 15 target compounds were 0.17-1.21ng/g.　　Nine laboratories from different industries were selected to conduct a comparative validation of the method. The testing results of statistical analysis indicated that the repeatability and reproducibility were essentially consistent with no significant differences. In order to investigate the applicability and accuracy of the method, the certified standard material for domestic sludge (SRM 2585) developed by the National Institute of Standards and Technology (NIST) was used for testing. The results of 9 laboratories participating in the collaborative verification were all within the uncertainty range, and the absolute value of the relative error was less than 5.35%, which indicates that this method can be applied to the analysis of actual samples.

The results show that this method is simple and accurate, and is suitable for the detection of flame retardants in different types of soil and sediment samples. This method can provide technical support for the environmental investigation and research of these organophosphate ester flame compounds.