Abstract
Hexabromocyclododecanes (HBCDs) are a group of brominated flame retardants that are extensively employed in the industrial production of plastics, furniture, and construction materials. Due to their regular use and massive emissions, HBCDs have been distributed in the environment (air, water, soil, and sediments). Due to their high toxicity, persistent and long-distance transport, and bioaccumulation, HBCDs were listed in the Stockholm Convention in 2013. Thus, the accurate analysis and strict control of the pollution levels of HBCDs in environmental samples are critical to the government's long-term environmental supervision mechanism. However, the concentration levels of HBCDs in real samples are low, combined with complex matrices, which seriously limits the determination of HBCDs. The target isomers are particularly transformed or degraded, which makes analysis challenging due to the high temperatures and specific organic solvents. The physicochemical features, toxic and environmental dangers, usage, and standard limitations of HBCDs are briefly discussed herein. Sample pretreatment and instrument detection of HBCDs in various matrices are summarized (i. e., soil, sediment, food, electronics, atmosphere, animals, and water). More than 70 research papers (2000-2022) from the Science Citation Index (SCI) and Chinese core publications are cited herein. First, the entire process of extraction, purification, separation, and enrichment of HBCDs is compared, including soxhlet extraction (SE), ultrasonic-assisted extraction (UAE), accelerated solvent extraction(ASE), supercritical fluid extraction (SFE), solid phase extraction (SPE), dispersed solid phase extraction (DSPE), liquid-liquid extraction (LLE), dispersive liquid-liquid microextraction (DLLME), and solid phase microextraction (SPME). In the literature, UAE is the most commonly employed process, accounting for a quarter of all HBCDs sample pretreatments. Additionally, SPE sample pretreatment technology can completely separate the targets and impurities to reduce the effect of matrix; and enrich the targets to improve sensitivity of method. By using SPE technology, the enrichment factor can be increased due to the massive sample volume, thus enabling detect HBCDs concentrations (nanogram per liter level) in water. Second, the advantages and disadvantages of instrument approaches are examined and discussed, including gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), liquid chromatography (LC), and liquid chromatography-tandem mass spectrometry (LC-MS/MS), which offer a reference for meeting the requirements in the determination of HBCDs in real samples, i. e., the total HBCDs can be detected by GC or GC-MS and three HBCD isomers (α-HBCD, β-HBCD, γ-HBCD) can be determined by LC or LC-MS. By using the triple quadrupole mass spectrometer, the sensitivity of the method can be improved. Till date, LC-MS/MS has been chosen as an instrument for the determination of HBCDs in various matrices (i. e., seawater, marine sediment, marine organisms, toys, and electronic products) in China. However, there are several challenges. The sample pretreatment is tedious; large sample volumes and organic solvent utilization. These challenges point to the development trends of analytical approaches for HBCDs. The development of green, automated, low-cost, fast, and efficient sample pretreatment approaches for new adsorption materials is the main development direction in the analysis of HBCDs in the future.
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