Chromatography Electron Capture Negative Ionization Research Articles

Short- and medium-chain chlorinated paraffins in sediment from the Haihe River Basin: Sources, distributions, and ecological risk assessment

Chlorinated paraffins (CPs) can accumulate in sediment and pose risks to ecological systems and human health. The Haihe River Basin is one of the seven main river basins in China and is mainly in the Beijing–Tianjin–Hebei region, which is densely populated and very urbanized. There is therefore a high probability of CP pollution in the Haihe River Basin. However, CP pollution and the environmental risks posed by CPs in the Haihe River are not well understood. In this study, the concentrations of short-chain CPs (SCCPs) and medium-chain CPs (MCCPs) in sediment from six rivers in the Haihe River Basin system were determined using two-dimensional gas chromatography electron-capture negative ionization mass spectrometry. The total SCCP and MCCP concentrations in the sediment samples ranged from 131.83 to 1767.71 and from 89.72 to 1442.82 ng/g dry weight, respectively. The total organic carbon content did not significantly correlate with the CP concentrations. The dominant SCCP congener groups were C10Cl6–7 and the dominant MCCP congener groups were C14Cl7–8. Significant relationships (R = 0.700, p < 0.05) were found between the SCCP and MCCP concentrations, indicating that SCCPs and MCCPs may have similar sources. Hierarchical cluster analysis and principal component analysis indicated that sediment in the study area was contaminated with CPs through the use of the CP-42 and CP-52 commercial products in industrial processes and human activities. The ecological risks posed by CPs were assessed and SCCPs were found to pose high risks in the Yongding New River but moderate risks in the other rivers. MCCPs were found to pose minimal risks to the aquatic environment at most of the sampling points.

Air–soil exchange of and risks posed by short- and medium-chain chlorinated paraffins: Case study in a contaminated area in China

Short-chain (SC) and medium-chain (MC) chlorinated paraffins (CPs) are found widely in the environment. Little research into air–soil exchange of SCCPs and MCCPs has been performed. In this study, CP concentrations, congener group profiles, and air–soil exchange in a typical contaminated area were investigated. A total of 10 soil samples and 10 air samples were collected from Zhoushan, an island in China. The samples were analyzed by two-dimensional gas chromatography electron capture negative ionization mass spectrometry. The SCCP and MCCP concentrations in the soil samples were 72–3842 and 117–8819 ng/g, respectively, and the SCCP and MCCP concentrations in the air samples were 57–208 and 1.8–25 ng/m3, respectively. The highest CP concentrations in both soil and air were found in samples from near shipyards, possibly because of CPs being emitted from metal cutting fluids and marine paints used at the shipyards. C14–15Cl7-9 were the dominant CP congener groups in the soil samples. C10Cl6–7 were the dominant CP congener groups in the air samples. Chlorinated decane and undecane and penta-, hexa-, and hepta-chlorinated CPs were enriched in the air relative to the soil. These congeners may have been released from the commercial CP-42 and CP-52. The fugacity fractions (ffs) of 48 homologs decreased as Koa increased. The ffs indicated that SCCPs and MCCPs dominated deposition. The net air–soil exchange fluxes of CPs were 201–769 ng/(m2·h). A preliminary risk assessment indicated that CPs pose low ecological risk except at sampling site S7 and do not pose significant health risks.

Liquid Chromatography-Electron Capture Negative Ionization-Tandem Mass Spectrometry Detection of Pesticides in a Commercial Formulation.

Negative chemical ionization (NCI) and electron-capture negative ionization (ECNI) are gas chromatography–mass spectrometry (GC–MS) techniques that generate negative ions in the gas phase for compounds containing electronegative atoms or functional groups. In ECNI, gas-phase thermal electrons can be transferred to electrophilic substances to produce M–• ions and scarce fragmentation. As a result of the electrophilicity requirements, ECNI is characterized by high-specificity and low background noise, generally lower than EI, offering lower detection limits. The aim of this work is to explore the possibility of extending typical advantages of ECNI to liquid chromatography–mass spectrometry (LC–MS). The LC is combined with the novel liquid-EI (LEI) LC–EIMS interface, the eluent is vaporized and transferred inside a CI source, where it is mixed with methane as a buffer gas. As proof of concept, dicamba and tefluthrin, agrochemicals with herbicidal and insecticidal activity, respectively, were chosen as model compounds and detected together in a commercial formulation. The pesticides have different chemical properties, but both are suitable analytes for ECNI due to the presence of electronegative atoms in the molecules. The influence of the mobile phase and other LC- and MS-operative parameters were methodically evaluated. Part-per-trillion (ppt) detection limits were obtained. Ion abundances were found to be stable with quantitative linear detection, reliable, and reproducible, with no influence from coeluting interfering compounds from the sample matrix.

Comparison of the PCB serum levels among mother-child pairs in areas of Eastern Japan and Central Taiwan

Polychlorinated biphenyls (PCBs) have been prohibited for two decades in Japan and Taiwan. The aim of this study was to compare the PCB congeners in maternal and cord serum between two countries. Our study subjects were 248 and 100 mother-child pairs in Japan and Taiwan. The measured levels of 23 serum PCB congeners between two countries were analyzed using gas chromatography–electron capture negative ionization quadrupole mass spectrometry (GC-NICI-qMS). The statistical comparisons were conducted by Student's t-test and principal component analysis with further stratification by maternal age and parity. The maternal total PCBs levels in Japan (426 ± 244 pg/g wet wt) were significantly higher than those in Taiwan (254 ± 155 pg/g wet wt), and the similar results were found in cord total PCBs levels (97 ± 76 and 58 ± 87 pg/g wet wt). It showed different distributions of PCB congeners between two countries. Whether in maternal or cord serum, the CB138, CB153 and CB180 were the highest detectable congeners whether in Japan or Taiwan. And, the CB66, CB99, CB206 and CB209 were only detected in maternal serum of Taiwan. The women of advanced maternal age had higher levels of PCB congeners, especially in Taiwan, and the primiparous women had higher levels of PCB congeners in two countries. In summary, the PCB congeners in Japan's mother-child pairs were with higher levels and different distributions when compared to those in Taiwan, and the maternal age and parity were important factors associated with the PCB levels.

Screening of halogenated phenolic compounds in plasma and serum from marine wildlife

The growing knowledge of the impact of halogenated phenolic compounds on hormonal and metabolic systems has led to an increased interest in the exposure and potential effects of these compounds in wildlife. In the present study, a screening procedure was developed to detect and quantify halogenated phenolic compounds in serum and plasma from marine wildlife. A mass spectral library containing selective ion monitoring data was created using gas chromatography electron capture negative ionization mass spectrometry. The selective ion monitoring data in the library were accompanied with retention indices to increase the specificity of each entry in the library. The library together with the developed extraction procedure and optimized instrumental settings can be used for the detection of 52 different halogenated phenolic compounds of environmental concern, including 23 hydroxylated polychlorinated biphenyls and 24 hydroxylated polybrominated diphenyl ethers. The instrument limit of detection for the compounds included in the library ranged from 30 to 320 fg/injection, with a median detection limit of 90 fg/injection. The average recovery of 11 different halogenated phenolic compounds, from four species of marine wildlife, was 66 ± 14%. A full-scan mass spectral library was also created containing an additional seven compounds. Gray seals, long-tailed ducks, and two species of fish from the Baltic Sea were screened for halogenated phenolic compounds using the developed procedure. A total of 33 compounds included in the library were detected and quantified.

Dietary Habits and Cooking Methods Could Reduce Avoidable Exposure to PCBs in Maternal and Cord Sera

Polychlorinated biphenyls (PCBs), like other persistent organic pollutants, are accumulating throughout the food chain and pose health threats to humans, especially children and foetuses. There is no protocol for reducing the contamination levels of the PCBs in humans. This study identified food items and cooking methods that reduce serum PCB levels by analysing data collected from the Chiba Study of Mother and Child Health. The sample size was 194 subjects. Serum PCB levels were measured using gas chromatography–electron capture negative ionization quadrupole mass spectrometry. Information on dietary habits was obtained from a brief diet history questionnaire that included questions about food items and cooking methods. Food items were categorized into food groups, and nutrient levels were calculated based on food item consumption. Principal component analysis and lasso regression were used as statistical methods. The analyses of food items and nutrients suggested that food items rich in dietary fibre reduce avoidable exposure to PCBs, as could grilling and deep frying of food, which could reduce avoidable exposure to serum PCBs in mothers and foetuses. (174 words).

Dietary exposure to short- and medium-chain chlorinated paraffins in meat and meat products from 20 provinces of China.

Food intake is one of the main pathways of human exposure to chlorinated paraffins (CPs). This study assessed the dietary exposure for the general Chinese population to short-chain chlorinated paraffin (SCCPs) and medium-chain chlorinated paraffins (MCCPs) through meat and meat products. Twenty samples of meat and meat products from 20 Chinese provinces were collected in 2011. As the sampling sites covered about two-thirds of the Chinese population, the meat samples were considered to be representative of the true characteristics of CPs contamination in Chinese meat products. The concentrations of SCCPs and MCCPs in the meat samples were measured using the comprehensive two-dimensional gas chromatography electron capture negative ionization high-resolution time-of-flight mass spectrometry method. Forty-eight SCCP and MCCP homolog groups were detected in the meat samples. The mean SCCP and MCCP concentrations in all meat samples were 129±4.1ngg-1 wet weight and 5.7±0.59ngg-1 wet weight, respectively. The concentrations of SCCPs and MCCPs varied in samples from different provinces. The geographical distribution of CP concentrations was similar to the distribution of CPs manufacturing plants in China. The most abundant groups of SCCPs in all samples were C10-11 Cl6-7, and the most abundant groups of MCCPs in most samples were C14 Cl7-8. The possible sources of SCCPs and MCCPs in meat and meat products might be CP-42 and CP-52. The 50th percentile estimated daily intakes of SCCPs and MCCPs through meat consumption for a "standard" Chinese adult male were 0.13 and 0.0047μgkg-1 bw d-1, respectively, both much lower than the tolerable daily intakes (TDIs) for SCCPs and MCCPs. This preliminary risk assessment has indicated that the indirect exposure of SCCPs and MCCPs through meat consumption does not pose significant risk to human health in China.

Measurement of urinary Benzo[a]pyrene tetrols and their relationship to other polycyclic aromatic hydrocarbon metabolites and cotinine in humans

Biomonitoring of exposure to polycyclic aromatic hydrocarbons (PAHs) typically uses measurement of metabolites of PAHs with four or less aromatic rings, such as 1-hydroxypyrene, even though interest may be in exposure to larger and carcinogenic PAHs, such as benzo[a]pyrene (B[a]P). An improved procedure for measuring two tetrol metabolites of B[a]P has been developed. Using 2 mL urine, the method includes enzymatic deconjugation of the tetrol conjugates, liquid-liquid extraction, activated carbon solid phase extraction (SPE) and Strata-X SPE, and gas chromatography–electron capture negative ionization–tandem mass spectrometric determination. Limits of detection were 0.026 pg/mL (benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydrotetrol, BPT I-1) and 0.090 pg/mL (benzo[a]pyrene-r-7,t-8,c-9,c-10-tetrahydrotetrol, BPT II-1). We quantified BPT I-1 and BPT II-1 in urine from a volunteer who consumed one meal containing high levels of PAHs (barbequed chicken). We also measured urinary concentrations of BPT I-1 and BPT II-1 in smokers and nonsmokers, and compared these concentrations with those of monohydroxy PAHs (OH-PAHs) and cotinine. Urinary elimination of BPT I-1 and BPT II-1 as a function of time after dietary exposure was similar to that observed previously for OH-PAHs. While the median BPT I-1 concentration in smokers’ urine (0.069 pg/mL) significantly differs from nonsmokers (0.043 pg/mL), BPT I-1 is only weakly correlated with cotinine. The urinary concentration of BPT I-1 shows a weaker relationship to tobacco smoke than metabolites of smaller PAHs, suggesting that other routes of exposure such as for example dietary routes may be of larger quantitative importance.

Health risks posed to infants in rural China by exposure to short- and medium-chain chlorinated paraffins in breast milk

Chlorinated paraffins (CPs) are complex mixtures of synthetic chemicals found widely in environmental matrices. Short-chain CPs (SCCPs) are candidate persistent organic pollutants under the Stockholm Convention. There should be great concern about human exposure to SCCPs. Data on CP concentrations in human breast milk is scarce. This is the first study in which background SCCP and medium-chain CP (MCCP) body burdens in the general rural population of China have been estimated and health risks posed to nursing infants by CPs in breast milk assessed. The concentrations of 48 SCCP and MCCP formula congeners were determined in 24 pooled human milk samples produced from 1412 individual samples from eight provinces in 2007 and 16 provinces in 2011. The samples were analyzed by comprehensive two-dimensional gas chromatography electron capture negative ionization high-resolution time-of-flight mass spectrometry. The median SCCP and MCCP concentrations were 303 and 35.7ngg−1 lipid weight, respectively, for the 2007 samples and 360 and 45.4ngg−1 lipid weight, respectively, for the 2011 samples. The C10 and C14 homologs were the dominant CP carbon-chain-length groups, contributing 51% and 82% of the total SCCP and MCCP concentrations, respectively. There are probably multiple CP sources to the general Chinese population and numerous exposure pathways. The median estimated daily SCCP and MCCP intakes for nursing infants were 1310 and 152ngkg−1d−1, respectively, in 2007 and 1520 and 212ngkg−1d−1, respectively, in 2011. SCCPs do not currently pose significant risks to infants in China. However, it is necessary to continuously monitor CP concentrations and health risks because CP concentrations in Chinese human breast milk are increasing.

Occurrence of chlorinated paraffins in house dust samples from Bavaria, Germany

Levels and distribution of chlorinated paraffins were studied in randomly taken house dust samples (<63 μm) from the greater area of Munich, Germany. Quantification of short- (SCCPs, C10–C13) and medium-chain chlorinated paraffins (MCCPs, C14–C16) were performed using gas chromatography electron capture negative ion mass spectrometry (GC–ECNI–MS). Concentrations of MCCPs in private household samples varied between 9 μg/g and 892 μg/g, and exceeded levels of SCCPs, which were in the range of 4–27 μg/g. Two dust samples from a public building contained up to 2050 μg/g SCCPs but no MCCPs. Among MCCPs, chlorinated tetradecanes were major components with a proportion of almost 50%. Among SCCPs, chlorinated dodecanes were usually present at higher concentrations than the congeners of any C10, C11, and C13 chains. The results indicate that particularly MCCPs may be present in relatively high concentrations in house dusts.

Multi-residue method for the determination of brominated and organophosphate flame retardants in indoor dust

A new method was optimized for the simultaneous determination of several flame retardants (FRs) in indoor dust, namely polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDs), novel brominated flame retardants (NBFRs) and organophosphate ester flame retardants (OPFRs). The method was based on two previously validated analytical methods for NBFRs and OPFRs, which were combined in order to include even a large number of FRs. An ultrasonic extraction method and two-stage clean-up by adsorption chromatography was optimized using an indoor dust standard reference material (SRM 2584). The 1st cleanup step was essential for fractionation of analytes in the dust extracts, while the 2nd step was important for the further removal of interferences. Analysis of cleaned dust extracts was performed with gas chromatography electron impact ionization mass spectrometry for OPFRs, gas chromatography electron capture negative ionization mass spectrometry for PBDEs and NBFRs and liquid chromatography electrospray ionization tandem mass spectrometry for HBCDs. Method validation by matrix spiking demonstrated good accuracy ranging from 81 to 130%. Matrix effects were investigated by spiking sodium sulfate and dust with analyte standards. Typical recoveries ranged between 80 and 110% at both spiking levels, though occasional deviations were observed at low spiking concentrations. Precision between different days was generally below 24% relative standard deviation (RSD) at low concentrations and below 11% RSD at high concentrations. Method limits of quantification for BFRs ranged between 0.04 (BDE 28) and 17ng/g (BDE 209), 6ng/g for sum HBCDs, and for OPFRs between 10 (triphenyl phosphate) and 370ng/g (tri-isobutyl phosphate). The method was applied to SRM 2585 and to a set of indoor dust samples from various countries. The newly developed method will be employed for the monitoring of human exposure via dust ingestion to phased-out and alternate FRs.

Determination of ultra-trace levels of priority PBDEs in water samples by isotope dilution GC(ECNI)MS using 81Br-labelled standards

A gas chromatography electron capture negative ionization mass spectrometry (GC(ECNI)MS) procedure for the determination of priority polybrominated diphenyl ethers (PBDEs; congeners 28, 47, 99, 100, 153 and 154) in water samples at regulatory EU levels has been developed. The method is based on the use of (81)Br-labelled PBDEs for isotope dilution analysis and the measurement of (79)Br/(81)Br isotope ratios in gas chromatography peaks with the electron capture negative ionization technique. The suitability of this ion source for the precise and accurate measurement of bromine isotope ratios has been demonstrated. The general ECNI-IDMS procedure was evaluated by the analysis of NIST SRM 1947 (Lake Michigan fish tissue) with satisfactory results. For the analysis of water samples, 500 mL of the samples were spiked with the labelled PBDEs and extracted with 10 mL isooctane for 30 min. The extract was evaporated down to ca. 100 μL and injected in the GC(ECNI)MS. Detection limits ranged from 0.014 (-1) to 0.089 pg mL(-1) depending on the congener. Recoveries from real water samples, spiked at a level of 0.5 pg mL(-1), ranged from 77% to 102%.

Comparison of quantification methods for the analysis of polychlorinated alkanes using electron capture negative ionisation mass spectrometry

Four quantification methods for short-chain chlorinated paraffins (SCCPs) or polychlorinated alkanes (PCAs) using gas chromatography electron capture negative ionisation low resolution mass spectrometry (GC-ECNI-LRMS) were investigated. The method based on visual comparison of congener group patterns of external standards used for quantification and fish samples was very sensitive for the choice of the quantification standard. Two other methods used the existing relation of the response factors with the chlorine content of SCCP mixtures for quantification. Results from the three methods above deviated from nominal values less than 20%. This was ∼50% when individual PCA standards were applied for quantification of SCCPs. The deviation is probably caused by the fact that only C10 carbon chain length standards with 5–9 chlorine atoms could be used. However, quantification using individual PCA standards is a promising method provided more standards will become commercially available. The clear advantage is that the standards are defined, which makes quantification comparable between different laboratories. Application of all four quantification methods to the analysis of four different fish samples gave results that agreed with the median values within ±40%.

Levels of Chlorinated Paraffins in Water

AbstractWastewater treatment plant influents, effluents, and river water samples were analyzed for chlorinated paraffins (CPs). CPs were not detected in river water samples, in effluents, and in filtered influents by using gas chromatography electron capture negative ion mass spectrometry (GC‐ECNI‐MS) (LOQ = 100 ng/L). However, middle chain chlorinated paraffins (MCCPs) were frequently present in suspended solid matter from influents while short chain chlorinated paraffins (SCCPs) were detected only in 2 of 15 samples. Concentrations of SCCPs and MCCPs measured by GC‐ECNI‐MS varied between n.d. and 4600 ng/L adsorbed on suspended solid matter.

Evaluation of Automated Stir Bar Sorptive Extraction-Thermal Desorption-Gas Chromatography Electron Capture Negative Ion Mass Spectrometry for the Analysis of PBDEs and PBBs in Sheep and Human Serum

Stir-bar sorptive extraction and automated thermal desorption/cryotrapping interfaced to capillary gas chromatography and electron capture negative ion mass spectrometry is shown to effectively isolate and recover polybrominated diphenyl ethers and polybrominated biphenyls from sheep and human serum. This paper describes the development of the method and demonstrates the feasibility of using Twister with spiked serum. Conditions for conducting stir-bar sorptive extraction and for automated thermal desorption that led to acceptable analyte recoveries were optimized. The approach to sample preparation introduced here significantly reduces tedious labor and solvent consumption associated with conventional liquid-liquid extraction.

Comparative evaluation of liquid chromatography–mass spectrometry versus gas chromatography–mass spectrometry for the determination of hexabromocyclododecanes and their degradation products in indoor dust

Domestic and office dust samples ( n = 37) were analyzed for hexabromocyclododecanes (HBCDs) using gas chromatography–electron-capture negative ionization–mass spectrometry (GC–ECNI/MS) and liquid chromatography–electrospray tandem mass spectrometry (LC–ESI/MS/MS). To determine the best method to quantify HBCDs using GC–ECNI/MS, BDE 128 was used as internal standard (I.S.) in all samples, while 13C-labeled α-HBCD was used as I.S. in some samples. Total HBCD concentrations (sum of α-, β-, and γ-HBCD diastereomers) were calculated using response factors (RFs) for α- and γ-HBCD as individual diastereomers and using an average RF for both diastereomers. Statistical comparison showed that concentrations obtained via GC–ECNI/MS were statistically indistinguishable ( p > 0.05) from those obtained using LC–ESI/MS/MS. The closest match between the two techniques was obtained using [ 13C]α-HBCD as I.S. and the average RF for α- and γ-HBCDs. Excellent linear correlations (Pearson coefficient values r > 0.9) were obtained between the GC–ECNI/MS and LC–ESI/MS/MS results, with slopes ranging from 0.76 to 1.36. Pentabromocyclododecenes (four isomers) and tetrabromocyclododecadienes (two isomers) were detected in the studied samples and were identified as degradation products of HBCDs after separation from the parent compound on the basis of both retention time and mass spectrum. This finding suggests that the elimination of HBr is the major degradation pathway for HBCDs in dust.

Fast analysis of decabrominated diphenyl ether using low-pressure gas chromatography–electron-capture negative ionization mass spectrometry

This paper reports the applicability of low-pressure gas chromatography–mass spectrometry operated in electron-capture negative ionization mode (LP-GC–ECNI-MS) for the analysis of decabrominated diphenyl ether (BDE-209). Particular attention was paid to find optimal injector and oven conditions for minimal thermal degradation of BDE-209. The analytical characteristics were compared for LP-GC columns (10 m × 0.53 mm) with different film thicknesses ( d f 0.15 μm versus 0.25 μm) and for a conventional GC column (15 m × 0.25 mm, 0.10 μm d f). Short residence times (6.5 and 9.8 min) of BDE-209 were found for the LP-GC systems with 0.15 and 0.25 μm d f, respectively, resulting in a low elution temperature and minimal degradation. Additionally, baseline separation of 22 polybrominated diphenyl ether (PBDE) congeners (major components of PBDE technical mixtures) was possible in less than 12 min using the LP-GC–ECNI-MS system with 0.15 μm d f. The optimized method was applied for the determination of PBDEs in Belgian indoor dust samples. The obtained concentrations of BDE-209 (range 8–292 ng/g dry weight) were in the same range or lower than concentrations in dust from other European countries.

Analysis of nitroaromatic compounds in complex samples using solid-phase microextraction and isotope dilution quantification gas chromatography–electron-capture negative ionisation mass spectrometry

A solid-phase microextraction (SPME) method using gas chromatography–electron-capture negative ionisation mass spectrometry (GC–ECNI-MS) and isotope dilution quantification for the analysis of nitroaromatic compounds in complex, water based samples has been optimised. For ionisation, ECNI was the most sensitive and selective method. SPME was compared to solid-phase extraction (SPE) and found to be more sensitive for these small volume samples. LODs were in the range 0.02–38 ng L −1 for SPME and 6–184 ng L −1 for SPE, respectively. The SPME method was applied on samples in the ng L −1 level from artificial reed beds treated with sludge containing residues from explosives and pharmaceuticals.

Characterization of polychlorinated n-alkanes using comprehensive two-dimensional gas chromatography–electron-capture negative ionisation time-of-flight mass spectrometry

Comprehensive two-dimensional gas chromatography with electron-capture negative ionization time-of-flight mass spectrometry (GC × GC–ECNI-TOF-MS) is used to study the composition and characteristics of short-, medium- and long-chain polychlorinated n-alkane (PCA) mixtures. Distinct ordered structures, which enable the highlighting and interpretation of group and sub-group separations are observed when using a DB-1 × 007-65HT column combination. The analysis of a number of, mutually rather different, technical mixtures and 35 individual standard compounds provides information on the role of chlorine substitution (number of substituents as well as their position), the contribution of carbon versus chlorine atoms to analyte volatility, i.e. GC × GC behaviour, and the influence of the chain length of the carbon skeleton. Two dust samples are analyzed to illustrate the practical usefulness of the proposed procedure.

Determination of dimetridazole and metronidazole in poultry and porcine tissues by gas chromatography–electron capture negative ionization mass spectrometry

A sensitive and selective method using gas chromatography–electron capture negative ionization mass spectrometry (GC–ECNI-MS) for analysis of dimetridazole (DMZ) and metronidazole (MNZ) in poultry muscles, porcine kidney and liver, and chicken liver, was developed and validated for the purpose of food surveillance testing of the residues of these two nitroimidazoles in various types of animal tissues in the Hong Kong Special Administrative Region. Before homogenization and extraction with toluene, [2H 3]dimetridazole-(DMZ-d 3) and secnidazole (SNZ) were added to tissue samples as internal standards. The organic extracts were mixed with n-hexane and subject to solid-phase extraction cleanup by amine extraction columns. MNZ and SNZ were derivatized with BSA prior to GC–ECNI-MS determination. Good recovery and precision were obtained and the limit of detection was below parts per billion levels for poultry and porcine tissues. The method could also be applied for the detection of the hydroxylated metabolite of DMZ.