Comparison and Analysis of Organochlorine Pesticides and Hexabromobiphenyls in Environmental Samples by Gas Chromatography–Electron Capture Detector and Gas Chromatography–Mass Spectrometry

Journal of Chromatographic Science 2015;53:197– 203 doi:10.1093/chromsci/bmu048 Advance Access publication May 28, 2014 Article Comparison and Analysis of Organochlorine Pesticides and Hexabromobiphenyls in Environmental Samples by Gas Chromatography –Electron Capture Detector and Gas Chromatography –Mass Spectrometry Yu Liu, Xiaofang Fu*, Shu Tao, Liang Liu, Wei Li and Bingjun Meng Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China *Author to whom correspondence should be addressed. Email: (X.F. Fu) Received 1 July 2013 Two analytical methods, gas chromatography – electron capture detector (GC – ECD) and gas chromatography – negative chemical ionization – mass spectrometry (GC – NCI-MS), were evaluated and compared for the measurement of persistent organic pollutants, specifically for 26 organochlorine pesticides and two hexabromobiphenyls, in atmospheric particulate matter and soil samples. The hypothesis tested was that the coelution of non-target compounds may lead to false positives when analyzed by GC–ECD, and that the overestimation associated with these false positives can be eliminated using GC–NCI-MS. The study showed that both methods had satisfactory linearity and reproducibility for the target compounds. Although the sensitivities of GC–ECD for most of the compounds investigated were higher than those observed with the GC–NCI-MS method, the matrices interference was obvious with GC–ECD. There was indeed an apparently high false-positive rate or overestimate when GC–ECD was used for environmental samples, implying that the GC–ECD method has been used with care and that GC–NCI-MS is generally superior for the analysis of trace amounts of these compounds in environmental samples. Based on these results, the sample extraction and cleanup procedures of the GC–NCI-MS method were optimized for achieving acceptable recoveries and less matrices interference. Introduction Persistent organic pollutants (POPs) are those compounds that are long-lasting and mobile in the environment and can be biomagnified in food chains (1). Because of the global concern, 21 POPs have been listed in the Stockholm convention on POPs (2, 3). Among those listed in the convention, organochlorine pesticides (OCPs) and hexabromobiphenyls (HBBs) are of particular concern, as OCPs had been widely applied in agricultural settings around the globe for decades, and HBBs had been widely used as flame retardants until they were banned in 2010 (4, 5). Despite the banning of most of these chemicals, both OCPs and HBBs are often detected in various environmental media in many places in China owing to their high persistence (6, 7). As volatile or semivolatile compounds, OCPs and HBBs in various environmental samples are most often measured using gas chromatography (GC), coupled with electron capture detector (ECD), which has a relatively higher sensitivity for many compounds compared with other detection devices (8 – 12). However, because of the complex matrices and trace amounts of analytes involved in environmental samples, matrices interference and false positives are always challenges in a GC –ECD-based procedure (13). In contrast, mass spectrometry (MS) has certain advantages over ECD for identifying specific compounds and reducing matrix interferences. In practice, GC – MS with electron ionization (GC – EI-MS) or negative chemical ionization (GC – NCI-MS) has been used for the determination of OCPs and HBBs in water and biological samples (14 – 16). GC, coupled with tandem mass chromatography (MS-MS), has also been applied to the analysis of HBBs in sediment, using programmable temperature vaporization and large volume injection (17). GC – NCI-MS-MS and GC with high-resolution mass spectroscopy (GC – HR-MS) have also been successfully used in the analysis of polybromobiphenyl (PBB) in biota (7). Unfortunately, in spite of the concern associated with possible false positives (13), GC –ECD is still widely used to analyze OCPs in food and environment (8, 18), largely due to its high sensitive and low cost. Because of these potential false-positives, it is possible that there has been an overestimation of OCP and HBB concentrations in the environment. Although there are many advanced methods such as GC – NCI-MS-MS or GC – HR-MS besides GC –NCI-MS, GC – NCI-MS has comparable lower cost and also could avoid many false-positive results to some extent. Therefore, in this work, we selected the GC – NCI-MS to determine the real sample and compare with that by GC–ECD. The primary objective of this study was to test and verify that non-target compounds can be coeluted in GC – ECD systems that could lead to a significant number of false positives when measuring OCPs and HBBs in air particulate matter (PM) samples and soil samples. Because any compounds with electron withdrawing groups have response on ECD detector. If the retention time of these non-target compounds is also same to that of target compounds, they will be identified the target OCPs or HBBs. These false-positive data will lead to the overestimation of these OCPs and HBBs. Although there are many methods to analyze OCPs and HBBs by GC – MS or GC – ECD, they did not compare the result between the two methods. There also has literature to mention the false-positive data with GC – ECD (13), but no specific date to certify the result. In this paper, the GC – NCI-MS method, together with a microwave-assisted extraction and cleanup procedure, was optimized with a two-layer column to develop an improved analytical method for the determination of OCPs and HBBs in the environment. Above all, direct comparison of the results by both GC – ECD and GC – NCI-MS analyses was investigated, and the specific data were presented to remind some environmental workers that there might be serious overestimate phenomena when the GC – ECD was used to determine the POPs in their research work, especially in trace analysis. # The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: Materials and methods Materials and chemicals 2,2 0 ,4,4 0 ,6,6 0 -hexabromobiphenyl (PBB155), 3,3 0 ,4,4 0 ,5,5 0 hexabromobiphenyl (PBB169), a mixed OCP standard containing aldrin, hexachlorocyclohexane isomers (HCHs, including a-, b-, g- and d-HCH), a-chlordane, g-chlordane, dichlorodiphenyltrichloroethane and metabolites (o, p0 -DDD, p, p0 -DDD, o, p0 -DDE, p, p0 -DDE, o, p0 -DDT and p, p0 -DDT), dieldrin, endosulfan I, endosulfan II, endrin, heptachlor, heptachlor exide (isomers A and B) (hep-ox(A) and hep-ox(B)), hexachlorobenzene (HCB), isodrin, methoxychlor, mirex, oxychlordane (all at a concentration of 10 mg mL21 in toluene), pentachlorobenzene ( pentachlb), pentachloronitrobenzene (PCNB) as an internal standard and 1-bromo-2-nitrobenzene (1-Br-2NP) as a surrogate for the target compounds were from AccuStandard (USA). Analytical grade acetone, n-hexane and d (...truncated)