Method development for analyzing ultratrace polyhalogenated carbazoles in soil and sediment

In the past few years, polyhalogenated carbazoles (PHCZs) have been of increasing concern because their structure is similar to that of legacy POPs. In the present study, an analytical method, including intensive cleanup and fractionation procedures in combination with instrumental parameters, was developed to determine ultratrace polyhalogenated carbazoles (PHCZs) in soil and sediment. The eluting sorbents, volume and packing of the column were optimized. Our results showed that 5 g of florisil and 4 g of silica gel under 150 mL of hexane/DCM = 3:1 presented good performance in terms of recovery and repeatability. GC-HRMS, GC-MS/MS (EI-MRM) and GC-MS (EI-SIM) were applied to compare the performance of PHCZ analysis. For sensitivity, EI-MRM presents method detection limits comparable to those of GC-HRMS and much lower than those of EI-SIM. Regarding selectivity, GC-HRMS performed better than the other two techniques since GC-HRMS can reduce interference from perfluorokerosene (PFK) and DDX (DDT, DDE, and DDD) due to its high resolution. GC-HRMS was then further optimized by shortening the run time and modifying the SIM ion. The final method was successfully applied to determine PHCZs in soil and sediment, and the target compounds had almost 100% detection frequency in the samples. The ubiquitous presence of PHCZ in soil and sediment calls for a further investigation of its source, distribution and degradation in the environment.