[Rapid determination of 15 N-nitrosamines in air-dried yak meat using one-step QuEChERS-gas chromatography-triple quadrupole mass spectrometry].

A method based on gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) coupled with one-step QuEChERS technique was developed for the simultaneous determination of 15 N-nitrosamines in air-dried yak meat. The hydration volume, extraction solvent, extracting salt, and cleaning material were optimized according to the characteristics of the N-nitrosamines and sample matrix. The optimized conditions were as follows: 10 mL of purified water for sample hydration, acetonitrile as the extraction solvent for the sample after hydration, 4.0 g of anhydrous MgSO4 and 1.0 g of NaCl as extracting salts, 500 mg of MgSO4+25 mg of C18+50 mg of PSA as cleaning materials. Favorable recoveries of the 15 N-nitrosamines were obtained when the extraction solution was incompletely dried. Thus, the final extract was dried to below 0.5 mL under a mild nitrogen stream and then redissolved to 0.5 mL with acetonitrile. After filtration, 200 µL of the sample was transferred to an autosampler vial for GC-MS/MS analysis. The 15 N-nitrosamines were determined using GC-MS/MS on a DB-HeavyWAX column (30 m×0.25 mm×0.25 µm) with an electron impact ion source in multiple-reaction monitoring (MRM) mode, and quantified using an external standard method. Under the optimized experimental conditions, the results showed that the calibration curves exhibited good linearities for the 15 N-nitrosamines, with correlation coefficients (r2) greater than 0.9990. The limits of detection (LODs) and the limits of quantification (LOQs) ranged from 0.05 to 0.20 µg/kg and from 0.10 to 0.50 µg/kg, respectively. At spiked levels of 1LOQ, 2LOQ, and 10LOQ, the average recoveries were 79.4%-102.1%, 80.6%-109.5%, and 83.0%-110.6%, respectively, and the relative standard deviations were in the range of 0.8%-16.0%. The low matrix effects of the 15 N-nitrosamines indicated the high sensitivity of the proposed method. The method was applied to detect representative commercial air-dried yak meat samples obtained using different processing techniques. Seven N-nitrosamines, including N-nitrosodimethylamine, N-nitrosodiisobutylamine, N-nitrosodibutylamine, N-methyl-N-phenylnitrous amide, N-ethyl-N-nitrosoaniline, N-nitrosopyrrolidine, and N-nitrosodiphenylamine were detected in all samples. The average contents of the seven N-nitrosamines was 0.08-20.18 µg/kg. The detection rates and average contents of the N-nitrosamines in cooked air-dried yak meat samples were higher than those in traditional raw air-dried yak meat samples. Compared with the manual QuEChERS method, the one-step QuEChERS method developed integrated the extraction and clean-up procedures into one single run, and the detection efficiency was considerably improved. The developed method is simple, rapid, highly sensitive, and insusceptible to human errors. Thus, it is useful for the determination of N-nitrosamines in air-dried yak meat and can be extended to the qualitative and quantitative analysis of N-nitrosamines in other meat products. It also provides method support and a data reference for the general determination of N-nitrosamines, which is of great significance for food safety.

[Determination of 35 prohibited pesticide residues in Saussurea costus by modified QuEChERS method based on multi-walled carbon nanotubes coupled with gas chromatography-tandem mass spectrometry].

Saussurea costus, a perennial herb belonging to the Asteraceae family, is a vital ingredient in traditional Chinese medicine. Increased demands for the herb have led to its widespread cultivation in China, but the corresponding increase in pesticide use has raised concerns about pesticide residues. Such residues would affect the safety and global market potential of Saussurea costus. Thus, a simple method is crucial to detect pesticide residues. The QuEChERS technique, in combination with gas chromatography-tandem mass spectrometry (GC-MS/MS), is commonly used for residue detection. However, traditional adsorbents may be unable to purify complex herbal mixtures well, affecting accuracy and instrument performance. Choosing suitable purification materials for Saussurea costus samples with complex matrices is of significant importance. This study focused on the detection of 35 prohibited pesticides in Saussurea costus. A rapid detection method was established by combining the QuEChERS technique with GC-MS/MS and utilizing a combination of multiwalled carbon nanotubes (MWCNTs), octadecylsilane-bonded silica gel (C18), and anhydrous magnesium sulfate (MgSO4) as the purification adsorbent. The samples were extracted with acetonitrile, purified by an improved QuEChERS process, subjected to GC-MS/MS analysis in multiple reaction monitoring (MRM) mode, and quantified using the internal standard method. The purification effects of four materials (C18, MWCNTs, N-propyl ethylenediamine (PSA), and graphitized carbon black (GCB)) and their optimal dosages were investigated by considering the matrix characteristics of the samples. An orthogonal experimental design was employed to optimize the ratio of adsorbent combinations, and the optimal adsorbent combination was determined to be 450 mg of MgSO4, 400 mg of C18, and 50 mg of MWCNTs. Matrix effect (ME) evaluation of the S. costus matrix showed that 31 target compounds strongly exhibited matrix-enhancement effects. Thus, matrix-matched calibration was employed in this study. Methodological investigation revealed that the standard curves for the 35 pesticides exhibited good linearity, with correlation coefficients (r2) greater than 0.9970. The average recoveries at three spiked levels ranged from 69.6% to 126.9%, and the relative standard deviations (RSDs) for parallel groups were all less than 10%. The limits of detection (LODs) and quantification (LOQs) ranged from 0.2 to 5.4 µg/kg and from 0.6 to 18.1 µg/kg, respectively. The developed method was used to screen and detect 35 pesticide residues in 20 batches of S. costus samples, and the target compounds were detected in six batches. The proposed method is simple, sensitive, and accurate. Thus, it is suitable for the rapid screening and detection of the 35 pesticide residues in S. costus and provides technical support for the cultivation, production, and quality control of the herb.

[Exposure characteristics and health risk assessment of 97 typical chemical pollutants in human serum].

Rapid industrial and agricultural developments in China have led to the wide use and discharge of chemical products and pesticides, resulting in extensive residues in environmental media. These residues can enter the human body through various pathways, leading to high exposure risks and health hazards. Because the human body is exposed to a variety of chemical pollutants, accurately quantifying the exposure levels of these pollutants in the human body and evaluating their health risks are of great importance. In this study, the serum concentrations of 97 typical chemical pollutants of 60 adults in central China were simultaneously determined using solid-phase extraction coupled with gas chromatography-tandem mass spectrometry (SPE-GC-MS/MS). In this method, 200 µL of a serum sample was mixed with 10 µL of an isotope-labeled internal standard solution. The sample was vortexed and refrigerated overnight at 4 ℃. Each sample was then deproteinized by the addition of 200 µL of 15% formic acid aqueous solution and vortexed. The serum sample was loaded into a preconditioned Oasis® PRiME HLB SPE cartridge and rinsed with 3 mL of methanol-water (6∶1, v/v). The SPE cartridge was subsequently vacuumed. The analytes were eluted with 3 mL of dichloromethane followed by 3 mL of n-hexane. The eluent was concentrated to near dryness under a gentle nitrogen stream and reconstituted with 100 µL of acetone. The samples were determined by GC-MS/MS and separated on a DB-5MS capillary column (30 m×0.25 mm×0.25 µm) with temperature programming. The column temperature was maintained at 70 ℃ for 2 min, increased at a rate of 25 ℃/min to 150 ℃, increased at a rate of 3 ℃/min to 200 ℃, and then held for 2 min. Finally, the column temperature was increased at a rate of 8 ℃/min to 300 ℃ and maintained at this temperature for 8 min. The samples were detected in multiple-reaction monitoring (MRM) mode and quantitatively analyzed using the internal standard method. Multiple linear regression models were used to analyze the effects of demographic characteristics, lifestyle habits, and diet on the concentrations of the chemical pollutants in the serum samples, and known biomonitoring equivalents (BEs) and human biomonitoring (HBM) values were combined to compute hazard quotients (HQs) and hazard indices (HIs) and evaluate the health risks of single and cumulative exposures to the chemical pollutants. The results showed that the main pollutants detected in human serum were organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). The detection rates of eight pollutants, including hexachlorobenzene (HCB) (100%), pentachlorophenol (PCP) (100%), p,p'-dichlorodiphenylene (p,p'-DDE) (100%), PCB-138 (100%), PCB-153 (98.3%), ß-hexachlorocyclohexane (ß-HCH) (91.7%), fluorene (Flu) (85.0%), and anthracene (Ant) (75.0%), were greater than 70%. The serum levels of ß-HCH were higher in females than in males, and age was positively correlated with exposure to p,p'-DDE, PCB-138, PCB-153, and ß-HCH. Increased exposure levels to p,p'-DDE and ß-HCH may be associated with a high frequency of meat intake, whereas increased exposure level to PCP may be associated with a high frequency of vegetable intake. The serum HQ of PCP was greater than 1 in 6.7% of the samples, and no risk was observed for HCB and p,p'-DDE exposure in the study population. Approximately 28.3% of the study subjects had HI values greater than 1. Overall, the general adult population in this region is widely exposed to a wide range of chemical pollutants, and gender, age, and diet are likely to be the main factors influencing the concentration of chemical pollutants. The health risk of single and compound exposures to chemical pollutants should not be ignored.

[Matrix solid-phase dispersion extraction of organophosphorus flame retardants in soil based on response surface methodology].

Organophosphorus flame retardants (OPFRs) are widely used in commercial products owing to their exceptional flame-retarding and plasticizing properties. However, OPFRs are also well recognized as emerging persistent organic pollutants (POPs) because of their environmental persistence, biological concentration, and potential toxicity. Thus, the accurate detection of OPFRs in environmental media is critical for analyzing their fate, transport, and ecological risk. However, very few OPFR detection methods are currently available, and the types of OPFRs detected may vary from site to site. In this study, matrix solid-phase dispersion extraction (MSPD), a simple, rapid, and versatile technique for preparing solid, semisolid, liquid, and viscous samples, was combined for the first time with gas chromatography-tandem mass spectrometry (GC-MS/MS) to analyze 10 OPFRs in soil, namely, tripropyl phosphate (TPrP), tri-n-butyl phosphate (TnBP), tri-iso-butyl phosphate (TiBP), tris(2-chloroisopropyl) phosphate (TCIPP), tris(2-chloroethyl) phosphate (TCEP), tris(1,3-dichloro-2-propyl) phosphate (TDCPP), triphenyl phosphate (TPHP), 2-ethylhexyl diphenyl phosphate (EHDPP), triphenylphosphine oxide (TPPO), and trimethylphenyl phosphate (TCP). The GC-MS/MS system was equipped with a Bruker-5MS capillary column coupled with a triple quadrupole mass spectrometer operated in multiple reaction monitoring (MRM) mode. Prior to detection, a mixed standard solution was fortified with 10 ng of13C-PCB208 as an internal standard. The optimal conditions under which MSPD could achieve high selectivity for OPFRs were determined. In addition, single-factor analysis was used to examine the influence of the sorbent (i. e., C18, PSA, Florisil, GCB, and multiwalled carbon nanotubes (MWCNTs)) as well as the dosage, type, and volume of the eluent on the extraction efficiency of the method for the 10 OPFRs. When GCB and ethyl acetate were used as the adsorbent and solvent, respectively, during elution, high extraction recoveries for the OPFRs were achieved. Optimization via response surface methodology (RSM) was adopted to further analyze the impact of three key factors, namely, the adsorbent dosage, eluent volume, and grinding time, as well as their interactions, on OPFR recoveries. Under the optimal conditions of 0.3 g of GCB as the adsorbent, 10 mL of ethyl acetate as the eluent, and 5 min of grinding time, the relative average recovery of the OPFRs was 87.5%. Furthermore, the 10 OPFRs showed good linear relationships under five concentration gradients, with correlation coefficients greater than 0.998. The limits of detection (LODs) and quantification (LOQs) were calculated as signal-to-noise ratios (S/N) of 3 and 10, respectively, and found to be in the ranges of 0.006-0.161 and 0.020-0.531 ng/g, respectively. The performance of the proposed method was verified by determining the recoveries and relative standard deviations (RSDs) of the OPFRs in soils spiked at low, medium, and high levels (10, 20, and 100 ng/g, respectively). The recoveries of the OPFRs ranged from 70.4% to 115.4%, with RSDs ranging from 0.7% to 6.7%. Compared with the conventional accelerated solvent extraction (ASE) method, MSPD presents higher efficiency, simpler operation, and less solvent requirements. The developed method was applied to determine OPFRs in soil samples collected from different sites in Suzhou, including an electronics factory, an auto-repair factory, a paddy field, and a school field. The results revealed that the contents of OPFRs in the soils from the electronics and auto-repair factories were significantly higher than those in the soils from the paddy and school fields. The main pollutants in the soil samples collected from the electronics and auto-repair factories were TCIPP, TPPO, TCEP, and TDCPP. Moreover, the contents of these compounds were 5.30, 4.44, 4.54, and 4.20 ng/g, in soils from the electronics factory and 2.70, 3.93, 7.60, and 5.04 ng/g, in soils from the auto-repair factory. To the best of our knowledge, this study is the first to determine high concentrations of TPPO in industrial soils. Thus, the combination of MSPD and GC-MS/MS adopted in this study can provide useful insights into the detection of the 10 OPFRs in soil.

[Determination of 15 preservative allergens in cosmetics by gas chromatography-tandem mass spectrometry].

Most preservatives are irritating and can easily induce skin sensitivities. Therefore, both domestic and international regulations impose clear restrictions on the use of preservatives in cosmetics. Herein, gas chromatography-tandem mass spectrometry (GC-MS/MS) was employed to simultaneously analyze the levels of 15 preservative allergens in cosmetics. Further, a precise identification approach based on a two-column retention index and mass spectrometry matching degree was developed. Cosmetic samples were extracted via acetonitrile vortex ultrasound extraction and then dehydrated with anhydrous MgSO4. The preservative allergens were separated on two columns, namely, DB-5MS and DB-WAX. Targets were identified using electron impact ionization (EI) source and the multiple reaction monitoring (MRM) mode and characterized using a retention index calibrated by a series of n-alkane standards. Following two tests, the LODs for the 15 preservative allergens on the DB-5MS column were in the range of 0.02-0.2 mg/kg, while those for 12 preservative allergens on the DB-WAX column were in the range of 0.01-20 mg/kg. The preservative allergens on the DB-5MS and DB-WAX columns demonstrated strong correlations, with all correlation coefficients exceeding 0.99. The recoveries for the 15 preservative allergens were in the range of 70.1%-129.8% at low, medium, and high levels, and the relative standard deviations (RSDs) were all below 15% (n=6) when using water, lotion, facial mask, and cream as the representative matrix. Next, 80 batches of genuine samples were tested using the established method. Isopropyl 4-hydroxybenzoate, a prohibited preservative, was detected in two sample batches using the DB-5MS and DB-WAX columns. Additionally, 11 and 10 restricted preservative allergens were identified on the DB-5MS and DB-WAX columns, respectively. The test results indicate that the double-column system approach offers excellent accuracy, effectively preventing false-positive and false-negative results, and can detect the 15 preservative allergens in cosmetics. The use of the retention index for the qualitative detection of these preservative allergens offers valuable options for non-targeted screening and meeting regulatory criteria.

Compatibility of cloud point extraction with gas chromatography: Matrix effects of Triton X-100 on GC-MS and GC-MS/MS analysis of organochlorine and organophosphorus pesticides.

Cloud point extraction is an environmentally benign and simple separation/concentration procedure that can be regarded as an alternative to classical liquid-liquid extraction. In the current work, it was studied the compatibility of cloud point extraction followed by back-extraction in low volume of organic solvent with gas chromatography-mass spectrometry (GC-MS and GC-MS/MS). Triton X-100 was preferred than Triton X-114 as a surfactant to produce the clouding phenomenon and hexane or isooctane was found to be appropriate organic solvents which can be used at the back-extraction step. It was observed that ca. 0.09 % w/w Triton X-100 was co-extracted in the organic phase (hexane or isooctane) so further study was carried out to find out its effect on the GC-MS (GC-MS/MS) measurement when liquid samples are injected without any pre-cleaning to remove the surfactant. The chromatographic separation and the mass detection were not deteriorated by the concomitant Triton X-100 for analysis of several Organochlorine and Organophosphorus pesticides (alpha-HCH, beta-HCH, gamma-HCH, Pentachlorobenzene, Hexachlorobenzene, Chlorpyrifos, Chlorpyrifos-methyl, Aldrin, Endrin, Dieldrin, alpha-Endosulfan, Heptachlor, Heptachlor-endo-epoxide-A, o,p-DDD, p,p-DDD, o,p-DDE, p,p-DDE, o,p-DDT and p,p-DDT). The stability of the GC system when introducing surfactant was assessed as acceptable (typically the peak area RSD% for 20 consecutive injections were below 5 %). Under the developed vaporization conditions using PTV or PSS injectors it can be deduced that Triton X-100 is deposited on the inner surface of the liner. This effect is beneficial since the resulting surfactant layer makes a surface which facilitates the pesticides transfer to the GC column. As a consequence, for some analytes, a substantial enhancement (up to 2.3 times) in the sensitivity was observed when the matrix-matched medium (0.09 % w/w Triton X-100 in organic solvent) is used compared to calibration in solely hexane or isooctane. Meanwhile, the measurement precision in the presence of Triton X-100 remains unchanged. The GC-MS/MS analysis was alternatively accomplished by the use of glass or metal liner and it was found that the glass one should be preferable. Finally, it can be concluded that cloud point extraction with Triton X-100 can be combined with GC-MS or GC-MS/MS analysis by applying liquid injection of the target analytes transferred in organic solvents such as hexane or isooctane. We have established a positive effect of Triton X-100 on the instrumental performance which is on opposite to the generally accepted concern of the negative influence of the surfactants on the gas chromatographic analysis.

Simultaneous determination of cyanide and thiocyanate in milk by GC-MS/MS using cetyltrimethylammonium bromide as both phase transfer catalyst and protein precipitant.

A method was developed for simultaneous determination of cyanide and thiocyanate in milk by gas chromatography-tandem quadrupole mass spectrometry (GC-MS/MS). Cyanide and thiocyanate were derivatized with pentafluorobenzyl bromide (PFBBr) as PFB-CN and PFB-SCN, respectively. Cetyltrimethylammonium bromide (CTAB) was employed both as a phase transfer catalyst and a protein precipitant in the sample pretreatment, which facilitates the separation of the organic and aqueous phases, and greatly simplifies the pretreatment procedures to achieve simultaneous and rapid determination of cyanide and thiocyanate. Under the optimized conditions, the limits of detection (LODs) of cyanide and thiocyanate in milk were 0.006 mg/kg and 0.015 mg/kg, and the spiked recoveries ranged from 90.1% to 98.2% and from 91.8% to 98.9% with relative standard deviations (RSDs) less than 18.9% and 15.2%, respectively. The proposed method was validated as a simple, fast and highly sensitive method for the determination of cyanide and thiocyanate in milk.

[High-throughput screening of multi-pesticide residues in animal-derived foods by QuEChERS-online gel permeation chromatography-gas chromatography-tandem mass spectrometry].

Improvements in living standards have led to an increase in the consumption of animal-derived foods. Pesticides may be used illegally during animal breeding as well as meat production and processing for pest control and preservation. Pesticides applied to crops may also be enriched in animal tissues through the food chain, thereby increasing the risk of pesticide residue accumulation in muscles and visceral tissues and endangering human health. China has stipulated maximum residue limits for pesticide residues in livestock and poultry meat and their viscera. Many other major developed countries and organizations, including the European Union, Codex Alimentarius Commission, and Japan, have also set maximum residue limits for these residues (0.005-10, 0.004-10, and 0.001-10 mg/kg, respectively). Research on pretreatment technologies for pesticide residue detection in plant-derived foods is widely available, but insufficient attention has been paid to animal-derived foods. Thus, high-throughput detection technologies for pesticide residues in animal-derived foods are limited. The impurities that can interfere with the detection process for plant-derived foods mainly include organic acids, polar pigments, and other small molecular compounds; by contrast, the matrix of animal-derived foods is much more complex. Macromolecular proteins, fats, small molecular amino acids, organic acids, and phospholipids can interfere with the detection of pesticide residues in animal-derived foods. Thus, selecting the appropriate pretreatment and purification technology is of great importance. In this study, the QuEChERS technique was combined with online gel permeation chromatography-gas chromatography-tandem mass spectrometry (GPC-GC-MS/MS) to determine 196 pesticide residues in animal-derived foods. The samples were extracted with acetonitrile, purified using the QuEChERS technique coupled with online GPC, detected by GC-MS/MS, determined in multiple reaction monitoring mode (MRM), and quantified using the external standard method. The effects of the extraction solvent and purification agent type on the extraction efficiency and matrix removal of the method were optimized. The purification effect of online GPC on the sample solution was investigated. The optimal distillate receiving time was obtained by studying the recoveries of the target substances and matrix effects over different distillate receiving periods to achieve the effective introduction of target substances and efficient matrix removal. Further, the advantages of the QuEChERS technique combined with online GPC were evaluated. The matrix effects of 196 pesticides were assessed; ten pesticide residues showed moderate matrix effects, while four pesticide residues showed strong matrix effects. A matrix-matched standard solution was used for quantification. The 196 pesticides showed good linearity in the range of 0.005-0.2 mg/L, with correlation coefficients greater than 0.996. The limits of detection and quantification were 0.002 and 0.005 mg/kg, respectively. The recoveries of 196 pesticides at spiked levels of 0.01, 0.05, and 0.20 mg/kg were 65.3%-126.2%, with relative standard deviations (RSDs) of 0.7%-5.7%. The proposed method is rapid, accurate, and sensitive; thus, it is suitable for the high-throughput screening and detection of multiple pesticide residues in animal-derived foods.

Comparison of gas chromatographic techniques for the analysis of iodinated derivatives of aromatic amines.

Some aromatic amines (AA) have been classified as carcinogens to humans. After entering the body, mainly through tobacco smoke, they can be detected in urine. Thus, their trace analysis as biomarkers in biofluids is of high relevance and can be achieved with gas chromatography (GC-MS), usually after derivatization. This study compares three gas chromatographic methods for the analysis of ten iodinated derivatives of AA: GC-MS in single-ion monitoring (SIM) mode with (1) electron ionization (GC-EI-MS) and (2) negative chemical ionization (GC-NCI-MS), and (3) GC-EI-MS/MS in multiple reaction monitoring (MRM) mode using electron ionization. All methods and most analytes showed good coefficients of determination (R2 > 0.99) for broad linear ranges covering three to five orders of magnitude in the picogram-per-liter to nanogram-per-liter range, with one and two exceptions for (1) and (2) respectively. Excellent limits of detection (LODs) of 9-50, 3.0-7.3, and 0.9-3.9 pg/L were observed for (1), (2), and (3) respectively, and good precision was achieved (intra-day repeatability < 15% and inter-day repeatability < 20% for most techniques and concentration levels). On average, recoveries between 80 and 104% were observed for all techniques. Urine samples of smokers and non-smokers were successfully analyzed, and p-toluidine and 2-chloroaniline could be found at significantly (α = 0.05) higher concentrations among smokers.

[Simultaneous determination of 28 fragrance components in cosmetics by gas chromatography-tandem mass spectrometry].

With the increasing number of cosmetic products, their flavor and fragrance components are receiving greater and greater attention. Establishing an analytical method of determining these components in cosmetics is one of the most effective measures to eliminate consumers' concerns. In this study, a method for the simultaneous determination of 28 fragrance residues in cosmetics by gas chromatography-tandem mass spectrometry (GC-MS/MS) was developed. The samples were extracted using methanol and those containing more oil and grease were purified using a neutral alumina solid-phase extraction column, whereas those with more complex compositions were purified by QuEChERS. The analytes in the samples were measured by GC-MS/MS, characterized using their retention times and characteristic ion pairs, and quantified with an external standard. The respective limits of detection (LODs, S/N=3) and quantification (LOQs, S/N>10) of the compounds were in the ranges 2-20 and 5-50 µg/kg. The linearities of the concentration curves of the 28 substances were good in the ranges 1-100, 2-200, 4-200, and 10-1000 µg/L, and the correlation coefficients of the quantitative ion pairs were >0.999. Twenty-eight fragrances were added to blank samples at spiked levels of 50-500 µg/kg, and the recoveries ranged from 71.3% to 120.4%, with RSDs of 1.5%-14.6%. The method could be applied in the determination of fragrances in cosmetics because it was simple, sensitive, and stable and could effectively exclude the interferences of complex matrices. The method was used to determine the fragrance components in 16 cosmetic products, and some fragrance components were detected in 12 samples. Increased attention should be paid to the safeties of fragrances and flavors used in cosmetics.

Translocation of Fungicides and Their Efficacy in Controlling Phellinus noxius, the Cause of Brown Root Rot Disease.

Brown root rot disease (BRRD), caused by Phellinus noxius, is an important tree disease in tropical and subtropical areas. To improve chemical control of BRRD and deter emergence of fungicide resistance in P. noxius, this study investigated control efficacies and systemic activities of fungicides with different modes of action. Fourteen fungicides with 11 different modes of action were tested for inhibitory effects in vitro on 39 P. noxius isolates from Taiwan, Hong Kong, Malaysia, Australia, and Pacific Islands. Cyproconazole, epoxiconazole, and tebuconazole (Fungicide Resistance Action Committee [FRAC] 3, target-site G1) inhibited colony growth of P. noxius by 99.9 to 100% at 10 ppm and 97.7 to 99.8% at 1 ppm. The other effective fungicide was cyprodinil + fludioxonil (FRAC 9 + 12, target-site D1 + E2), which showed growth inhibition of 96.9% at 10 ppm and 88.6% at 1 ppm. Acropetal translocation of six selected fungicides was evaluated in bishop wood (Bischofia javanica) seedlings by immersion of the root tips in each fungicide at 100 ppm, followed by liquid or gas chromatography tandem mass spectrometry analyses of consecutive segments of root, stem, and leaf tissues at 7 and 21 days posttreatment. Bidirectional translocation of the fungicides was also evaluated by stem injection of fungicide stock solutions. Cyproconazole and tebuconazole were the most readily absorbed by roots and efficiently transported acropetally. Greenhouse experiments suggested that cyproconazole, tebuconazole, and epoxiconazole have a slightly higher potential for controlling BRRD than mepronil, prochloraz, and cyprodinil + fludioxonil. Because all tested fungicides lacked basipetal translocation, soil drenching should be considered instead of trunk injection for their use in BRRD control.

[Hollow bimetal-organic framework material as solid-phase microextraction fiber coating for highly sensitive detection of polycyclic aromatic hydrocarbons].

Polycyclic aromatic hydrocarbons (PAHs) are among the most harmful persistent organic pollutants that possess high carcinogenicity and teratogenicity; hence, establishing a highly sensitive analytical method for monitoring PAHs in environmental samples is an urgent need. However, due to the low PAHs content in environmental samples and the complex matrix of the samples, it is difficult to directly determine the amount of PAHs using the existing analytical instruments. Therefore, an essential pretreatment of environmental samples should be carried out before instrumental analysis. In most pretreatment techniques, the extraction efficiency depends on the characteristics of the extraction materials. Currently, metal-organic framework materials (MOFs), which are porous materials self-assembled by metal ions and organic ligands, are used as solid-phase microextraction (SPME) coating materials for the extraction of PAHs. However, the following problems limit the application of MOFs in the SPME field: (1) MOF coating materials often require a long equilibration time for extraction because the it is difficult for the target to reach the deep adsorption sites; (2) In addition, most MOFs are formed by the coordination of single metal ions with organic monomers. The single type of open metal active sites is not conducive for realizing high extraction performance. In this study, a hollow bimetal-organic framework (H-BiMOF) was synthesized by the solvothermal method and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption-desorption analysis, thermogravimetric analysis, etc. The TEM images and XRD patterns demonstrated the successful synthesis of H-BiMOF with a hollow structure, which was formed through the competitive coordination between benzoic acid and water. The H-BiMOF material showed type-Ⅳ isotherms with a surface area of 1437 m2/g and excellent thermal stability. Subsequently, a H-BiMOF-coated SPME fiber was prepared by the physical adhesion method and used to extract trace PAHs from environmental samples. Due to the hollow structure of H-BiMOF, the prepared fibers offer the advantages of high utilization of specific surface area as well as short mass transfer distance, so that the extraction process quickly reaches equilibrium. At the same time, the introduction of bimetals provides a variety of metal active sites, which improves the extraction efficiency of the fiber against electron-rich cloud targets such as PAHs. The prepared fiber also had good service life, with at least 150 cycles. Combined with gas chromatography-tandem mass spectrometry (GC-MS/MS), a new method for the determination of PAHs in environmental water samples was established. Single factor experiments were performed to investigate the effects of the SPME conditions on the analytical performance. Under the optimal conditions, the established method showed low limits of detection (0.01-0.08 ng/L), wide linear range (0.03-500.0 ng/L), good linearity (correlation coefficients≥0.9986), and acceptable reproducibility (relative standard deviations≤9.8%, n=5). Finally, typical water samples were analyzed by the established method. Four environmental water samples were collected from Dianchi Lake, Poyang Lake, Taihu Lake, and Xihu Lake in China. No benzo(a)anthracene (BaA) and chrysene (CHR) were detected in any of the water samples. However, 17.9 ng/L of fluorene (FLU) and 5.3 ng/L of phenanthrene (PHE) were found in the Poyang Lake sample; 11.3 ng/L of fluoranthene (FLA) and 24.2 ng/L of pyrene (PYR) were found in the Taihu Lake sample; 50.0 ng/L of FLU, 19.5 ng/L of PHE, 14.9 ng/L of anthracene (ANT), 34.2 ng/L of FLA, and 44.5 ng/L of PYR were found in the Xihu Lake sample. The contents of the PAHs detected in all the lake water samples were lower than the Chinese National Standard GB 5749-2006 (2000.0 ng/L). The results of this study indicate that the developed method is suitable for the sensitive detection of trace levels of PAHs in real environmental water samples.

[Determination of polychlorinated naphthalenes in soil using accelerated solvent extraction-molecular sieves solid-phase extraction coupled with gas chromatography-tandem mass spectrometry].

Emerging pollutants (EPs) are chemical substances that are commonly not regulated and can be detected at low or very low concentrations. However, EPs have triggered special concern because their long-term adverse effects on the environment and human health remain unknown. Most EPs show biological toxicity, environmental persistence, and bioaccumulation. Even at low concentrations in the environment, EPs may pose significant environmental and health risks. Therefore, their treatment has been explicitly included in the 14th Five Year Plan for National Economic and Social Development of the People's Republic of China and the Outline of the Long-term Goals for 2035. Soil is a source of pollutants, and its quality is directly related to economic development, ecological security, and people's livelihood. At present, China's soil environmental monitoring system is not perfect, and the ability to monitor these new organic pollutants is lagging. Therefore, to strengthen the supervision of construction and agricultural land soil environments, it is essential to strengthen the soil environment monitoring ability for these EPs and establish a reliable, steady, and economic analysis method, including their separation and analysis methods in soil. Polychlorinated naphthalenes (PCNs) have received considerable attention as emerging halogenated compounds. They were listed in Annexes A and C of the Stockholm Convention on persistent organic pollutants (POPs) in 2015 because of their persistence, multimedia fate, and toxicity. PCNs have now been detected in the surrounding soils. Owing to their trace levels in complex soil, high requirements have been put forward for the pretreatment and instrument analysis of PCNs. This study aims to develop a new method for the selective purification of PCNs in soil, which can not only effectively remove lipids and other interferences in soil but also effectively reduce time, labor, and material costs in the pre-treatment process. Based on the physicochemical properties of the 13X molecular sieve, it was explored to purify soil-extracts as solid-phase extraction (SPE) sorbents. With n-hexane as the loading and rinsing solvent, 10 mL of a dichloromethane/n-hexane mixture (2∶15, v/v) was used to elute the PCNs. Moreover, selective separation of target substances from lipid macromolecules and other interferences could be achieved simultaneously. For the selective separation of PCNs, the average recovery of the internal standard could reach 56.1% to 88.0%. 13X molecular sieves are superior to gel permeation chromatography (GPC) and Florisil SPE, and they exhibit good cleanup efficiency similar to a multilayer silica gel/alumina column (53.0%-117.0%). Although the obtained recoveries are not as high as those obtained with a multilayer silica gel/alumina column, 13X molecular sieves have advantages in terms of simple operation, environmental friendliness, and low cost. Based on these fundamental experiments, accelerated solvent extraction was used to extract targets in soil, molecular sieves were used as SPE sorbents for purification, and GC-MS/MS was employed for PCN analysis. This method was developed as a systematic analytical method for PCNs determination. The method detection limits (MDLs) for PCN homologs were in the range of 0.009-0.6 ng/g. The precision and accuracy of the method were evaluated using spiked matrices. At three spiked levels (4, 10, and 18 ng), the recoveries of PCNs (CN-3, 13, 42, 46, 52, 53, 73, and 75) were 70%-128%, 71%-115%, and 61%-114%, respectively, and the corresponding relative standard derivations were 4.2%-23%, 6.5%-31% and 4.7%-22%. Thus, this method meets the requirements of trace analysis and shows acceptable parallelism, sensitivity, accuracy, and precision, thus being feasible for the analysis of emerging pollutant. The method is expected to play an important role in sample pretreatment in the future, especially for the nationwide investigation of soil pollution.

[Rapid screening of 84 pesticide residues in dendrobium by Sin-QuEChERS Nano purification column with gas chromatography-tandem mass spectrometry].

A rapid screening method for 84 pesticide residues in dendrobium perfringens parent material with different polarities was developed using a Sin-QuEChERS Nano clean-up column combined with gas chromatography-tandem mass spectrometry (GC-MS/MS). The differences in extraction efficiency of the targets were compared with different extraction solvents (acetonitrile containing 1% acetic acid, acetone) and methods (immersion with or without water). The purification effect and extraction recoveries of Sin-QuEChERS Nano method and classical dispersive solid-phase extraction (dSPE), solid-phase extraction (SPE) and QuEChERS were systematically compared using Dendrobium nobile samples. The differences in matrix effects between the Sin-QuEChERS Nano method, which was more effective in purification, and the dSPE method were also analyzed. The purification effects of three commercially available Sin-QuEChERS Nano purification columns (simple matrix purification column, complex matrix purification column and herbal purification column) were compared. The applicability of the purification methods were also verified by using different parts of Dendrobium nobile samples (stems, leaves and flowers). From the results, it could be concluded that weighing 2.00 g and the samples in 5 mL of water for 20 min, followed by extraction with acetonitrile containing 1% acetic acid was more effective. The average extraction recovery of the target components by Sin-QuEChERS Nano purification method was 90.5%, which further identified Sin-QuEChERS Nano-Chinese medicine purification column as the preferred purification column for dendrobium purification. The target components were separated by a DB-1701MS quartz capillary column (30 m×0.25 mm×0.25 µm) with programmed temperature rise, detected by multiple reaction monitoring (MRM) mode, and quantified by matrix-matched solution external standard method. The GC-MS/MS assay was used for the methodological validation of the 84 representative pesticides within Dendrobium officinale and Dendrobium nobile was carried out by GC-MS/MS detection method. The results indicated that the targets showed excellent linear correlation in different scopes with correlation coefficients (r2) >0. 990. The limits of detection (LODs, S/N=3) of the method were 1.5 to 5.8 µg/kg, and the limits of quantification (LOQs, S/N=10) ranged from 5.0 to 15.0 µg/kg. The spiked recoveries of the target pesticides under different spiked levels were 68.7%-116.2%, and the relative standard deviations (RSDs, n=6) were less than 15%. Compared to other typical pretreatment methods, the Sin-QuEChERS Nano method provided better performance in terms of purification. The method not only effectively removed pigments, organic acids, and alkaline interferents, but also saved preparation time. Losses due to solvent transfer were also avoided and no further vortexing or centrifugation was required, making it a simplified and effective extraction and purification procedure. The method was sensitive, rapid, simple and reliable. It effectively improved the detection efficiency during the rapid screening of pesticides in dendrobium and presented a strong practical application value. In addition, the developed method could further expand the types of target pesticides and could be used to detect more pesticide residues in foods and Chinese herbal medicine. The established Sin-QuEChERS Nano method was used for the analysis of authentic samples. The applicability of the method was evaluated by analyzing a total of 80 samples collected from Anlong, Libo, Dushan, and Yanhe County in Guizhou Province. The types of samples included dendrobium maple, Dendrobium nobile (flowers, stems, leaves) and Dendrobium officinale (flowers, stems, leaves, powder, tablets). At least one pesticide residue was detected in 12 samples, with a detection rate of 15%. The five pesticides with higher detection rates and residues were chlorpyrifos (0.08-0.5 mg/kg), chlorothalonil (0.06-3.2 mg/kg), propanil zinc (0.03-0.15 mg/kg), methyl parathion (0.04-0.23 mg/kg) and cyhalothrin (0.10-2.68 mg/kg). Except for the pesticides in maximum residue limits (MRLs), the pesticide residues detected from dendrobium samples were below the limits set by Chinese national standard (GB 2763-2021) and local standard DBS 52/048-2020.

[Simultaneous determination of seven dimethylcyclosiloxanes in cosmetics of different formulation systems by gel permeation chromatography purification-gas chromatography-tandem mass spectrometry].

At present, the addition of dimethylcyclosiloxanes (DMCs) in cosmetics is being debated and no substantial progress has been made in their safety risk assessment because of the lack of a suitable analytical method. Therefore, it is of theoretical and practical significance to establish a method suitable for the determination of DMCs in cosmetics with different formulation systems. Accordingly, a method based on gel permeation chromatography (GPC) purification combined with gas chromatography-tandem mass spectrometry (GC-MS/MS) was developed for the determination of seven DMCs in cosmetics. The cosmetic samples were extracted by ethyl acetate-cyclohexane (1∶1, v/v), purified by gel permeation chromatography, separated on a DB-5ms column (30.0 m×0.25 mm×0.25 µm), confirmed and detected by gas chromatography-tandem mass spectrometry in the selected reaction monitoring (SRM) mode, and quantified by the internal standard method with n-hexadecane as the internal standard. Experiments were carried out using n-tetradecane, n-hexadecane, and n-octadecane as the internal standards, and based on the retention time in GPC and GC, n-hexadecane was found to be the suitable choice for further analyses. The extraction efficiency for the target compounds was tested in different solvents such as methanol, n-hexane, acetonitrile, ethyl acetate, and ethyl acetate-cyclohexane (1∶1, v/v). Given the high recovery, ethyl acetate-cyclohexane (1∶1, v/v) was selected as the extraction solvent for analyses. Among the three purification methods (analysis without purification, solid-phase extraction (SPE), and GPC purification), GPC was selected as the best method because of the minimal matrix interference to the target compounds. Under the optimized conditions, the seven DMCs showed good linearities in the range of 0.05-1.0 mg/L. The correlation coefficients (r) were 0.994-0.998, which were greater than the required of the specification (r≥0.990). The limits of detection (LODs, S/N=3) were 0.04-0.08 mg/kg, and the limits of quantification (LOQs, S/N=3) were 0.12-0.24 mg/kg. According to the cosmetic matrix in different formulation systems, standard addition recovery tests at three levels of low, medium, and high were carried out. The average recovery rates of the targets were 85.3%-108.8%. The relative standard deviations (RSDs, n=6) were 3.1%-9.4%. The established method was also employed for the analysis of cosmetics in the market, and octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) were detected at various levels in the cosmetics. The method established in this study has the advantages of operational simplicity, high sensitivity, and good reproducibility, and it allows for the determination of seven DMCs in cosmetics with different formulation systems. The establishment of this method provides a basis for the quality supervision and inspection of DMCs in cosmetics in China, in addition to providing technical support for follow-up health and safety evaluation.

[Simultaneous determination of 35 organochlorine pesticides and polychlorinated biphenyls in the serum of the general population in Wuhan by solid phase extraction-gas chromatography-tandem mass spectrometry].

Owing to their persistence, ease of accumulation in organisms, and high toxicity, the use of persistent organic pollutants (POPs) has been limited ever since the Stockholm Convention on Persistent Organic Pollutants was signed in 2001 by the United Nations Environment Programme (UNEP). As typical POPs, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) can persist in the environment for long periods. They can enter human bodies through many pathways and pose a high exposure risk to humans. OCPs and PCBs can lead to endocrine disruption, neurotoxicity, immunotoxicity, reproductive toxicity, and cancer in human beings. Accurate quantification of pollutant load levels in vivo is crucial for the evaluation of health effects. In this study, a rapid and sensitive method based on solid phase extraction-gas chromatography-tandem mass spectrometry (SPE-GC-MS/MS) was developed for the simultaneous determination of 35 OCPs and PCBs in serum. Accordingly, 100 µL of the serum sample was gently mixed with the isotope-labeled internal standard solution (10 µL) to obtain a final mass concentration of 10 ng/mL for each internal standard. After incubation overnight, the samples were mixed with 100 µL purified water for dilution. After protein precipitation with 100 mg urea, the serum samples were passed through preconditioned Oasis® HLB cartridges, washed with 6 mL purified water, and eluted with 5 mL hexane-dichloromethane (1∶1, v/v). The SPE eluant was collected, evaporated to near dryness under a gentle nitrogen stream, and dissolved in 100 µL n-hexane. The reconstitution in the vial insert was injected into the GC-MS/MS instrument for analysis. The analytes were separated on an Agilent J&W DB-5MS capillary column (30 m×0.25 mm×0.25 µm) with temperature programming. The mass spectrometer was operated in the electron ionization (EI) mode. The optimal mass spectrometry conditions were realized by optimizing the instrument parameters such as ion pairs and collision energies. The analytes were detected in the multiple reaction monitoring (MRM) mode, and the internal standard method was used for quantitative analysis. The OCPs and PCBs had good linearities in the range of 0.05-50.0 ng/mL. The limits of detection (LODs, S/N=3) ranged from 1.2 to 71.4 ng/L. The recoveries of the 35 compounds were 72.6%-142% with relative standard deviations (RSDs) of less than 25% at the three spiked levels. The developed SPE-GC-MS/MS method was successfully applied to the simultaneous analysis of OCPs and PCBs in serum samples obtained from the general population in Wuhan. The results showed that the general population in Wuhan was widely exposed to OCPs and PCBs, especially the former. The detection frequencies of eight OCPs and seven PCBs were greater than 50%, and p,p'-DDE, p,p'-DDD, and methoxychlor were detected in all serum sample pools. Non-dioxin-like PCBs (NDL-PCBs) were the dominant PCB congeners, while PCB-28, PCB-153, and PCB-52 were the dominant PCBs in the general population of Wuhan. The concentration of OCPs increased with age. Moreover, the concentration of OCPs in individuals who were more than 66 years old was significantly higher as compared to that in younger individuals. The positive association differing by gender was significant in individuals over 60 years of age. There were no significant differences in PCB concentrations according to gender or age. There were no seasonal differences in the residue levels of OCPs and PCBs in the general population of Wuhan. The developed method is rapid and sensitive; it has the advantages of low limits of detection, satisfactory recoveries, accurate precision, and microsample volume, thus allowing for the simultaneous analysis of trace OCPs and PCBs in microserum samples in epidemiological studies. This robust analytical method also provides a powerful tool for the health risk assessment of OCP and PCB exposure.

[Modified QuEChERS method based on multi-walled carbon nanotubes coupled with gas chromatography-tandem mass spectrometry for the detection of 10 pyrethroid pesticide residues in tea].

A modified QuEChERS method, based on multi-walled carbon nanotubes (MWCNTs), was established for the detection of 10 pyrethroid pesticides (cyfluthrin, flucythrinate, fenpropathrin, bifenthrin, cyhalothrin, permethrin, cypermethrin, etofenprox, fenvalerate, deltamethrin) in tea, in combination with gas chromatography-tandem mass spectrometry (GC-MS/MS). The purification effects and dosages of four carbon nanomaterials, viz. single-walled carbon nanotubes (SWCNTs), MWCNTs, amino-modified MWCNTs, and graphene, were compared. An orthogonal experimental design was used to determine the optimal experimental conditions for sample pretreatment. The experimental factors governing the process were analyzed using variance. The results showed that the optimized sample pretreatment parameters were as follows. Acetonitrile was used as the extraction solvent with ultrasonic extraction for 35 min, while 60 mg MWCNTs, 200 mg PSA, and 200 mg C18, were used as purifiers. The effects of the extraction solvent and the carbon nanomaterials used on the recoveries of the 10 pyrethroid pesticides were significantly different (p<0.001), and the effect of extraction time on the recoveries was statistically different (p<0.05). The dosage of carbon nanomaterials had no significant effect on the recoveries (p>0.05). Good linearities were observed for the 10 pyrethroid pesticides in the concentration range of 0.01-2 mg/L. The limits of detection (LODs) and limits of quantification (LOQs) were in the ranges of 0.001-0.01 mg/kg and 0.005-0.04 mg/kg, respectively. The average recoveries of the pyrethroid pesticides spiked into blank samples of green tea were 91.4%-109.7%, and the relative standard deviations were 0.12%-9.80% (n=6). Furthermore, the matrix effects (MEs) of scented green tea, green tea, and black tea were evaluated. It was found that the addition of MWCNTs to the purifier can effectively reduce the matrix effect in green tea and black tea matrices. The developed method and the national standard method were used to detect the residues of the 10 pyrethroid pesticides in 120 tea samples available in the market. The results showed that cyfluthrin, deltamethrin, fenvalerate, permethrin, fenpropathrin, cypermethrin, bifenthrin and cyhalothrin were detected, and the contents obtained with the two methods were similar. Although pyrethroids were detected in most tea samples, the contents of all pesticide residues were below the maximum residue limits (MRLs). Therefore, the developed method is suitable for the rapid quantitative analysis of pesticide residues in tea.

[Simultaneous determination of 11 volatile perfluorinated compound precursors in textiles using gas chromatography-triple quadrupole mass spectrometry].

Perfluorinated compounds (PFCs) are persistent organic compounds. PFCs are artificially prepared hydrocarbons in which hydrogen atoms are completely replaced by fluorine. PFCs have excellent thermal stability and chemical stability, high surface activity, and hydrophobic and/or oleophobic properties owing to their exceptionally strong C-F bonds, low polarizability, and weak intermolecular van der Waals interactions. Currently, PFCs and their precursors are widely used in textile production as finishing agents and surfactants. In recent years, increasing attention has been devoted to PFCs and their precursors. In many countries and regions, such as the European Union, Canada, Denmark, and the United States, directives and regulations have been issued to restrict the use of PFCs and their precursors; the number of these compounds in such lists is increasing continuously. Studies have shown that PFCs are hepatotoxic, embryotoxic, reproductive-toxic, neurotoxic, and carcinogenic, and can interfere with the endocrine system, change animal instinct behavior, and potentially induce developmental neurotoxicity in humans, especially in young children. However, there are few established methods for the simultaneous detection of multiple PFC precursors, necessitating the same particularly for textiles. In this study, a method was developed for the simultaneous determination of 11 volatile PFC precursors in textiles using gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS). The target compounds included four fluorotelomer alcohols (FTOHs), three fluorotelomer acrylates (FTAs), two fluorooctane sulfonamides (FOSAs), and two fluorooctane sulfonamide-ethanols (FOSEs). Studies have shown that FTOHs and FTAs are precursors of perfluorocarboxylic acid, and FOSAs are precursors of perfluorooctanesulfonic acid. Some PFC precursors are converted into perfluorocarboxylic acid and perfluoroalkyl sulfonic acid, which threaten human health and ecological security. In this study, an effective ultrasonic-assisted extraction method for the 11 target compounds was established. The effects of the extraction solvent, extraction temperature, and extraction time on the extraction efficiency were investigated. The optimum extraction conditions for the developed method were carrying out ultrasonic extraction at 70 ℃ for 60 min with methanol as the extraction solvent. Separation was performed on a VF-WAXms capillary column (30 m×0.25 mm×0.25 µm) with temperature programming, following which the target compounds were detected by GC-MS/MS in the multiple reaction monitoring (MRM) mode and quantified using the external standard method. The matrix effects of three textile matrices were also investigated. The calibration curves of the 11 volatile PFC precursors showed good linearity in the concentration range of 10-500 µg/L with correlation coefficients not less than 0.9984. The limits of detection were 0.002-0.04 mg/kg (S/N=3), and limits of quantification were 0.006-0.1 mg/kg (S/N=10). The recoveries for the 11 analytes in different textile matrix samples at three spiked levels ranged from 73.2% to 117.2% with relative standard deviations (RSDs) of 0.1%-9.4% (n=6). Through actual sample analysis, four PFC precursors were detected in the textile product samples. The method has the advantages of simple pretreatment, accurate qualitative and quantitative analysis, high sensitivity, and good reproducibility. It can be effectively used for the simultaneous determination of 11 volatile PFC precursors in textiles. The establishment of this method has theoretical and practical significance for controlling PFC precursor levels in textiles. This study offers a new testing method for mitigating risk to safety and controlling textile products. It also provides a reference for establishing testing standards for PFC precursors in textiles and other similar consumer goods.

[Determination of nine N-nitrosamines in animal derived foods by QuEChERS-isotope dilution combined with gas chromatography-tandem mass spectrometry].

In this study, a comprehensive analytical method based on gas chromatography-tandem mass spectrometry (GC-MS/MS) was developed for the determination of nine N-nitrosamines in animal derived foods. There are many kinds of N-nitrosamines in foods that are harmful to human health. However, the national standard GB 5009.26-2016 pertains only to the detection of N-dimethylnitrosamine; there are many drawbacks of this method, such as complicated sample preparation, low recovery rate, and poor reproducibility. Hence, it is of practical significance to establish a method for the simultaneous determination of a variety of N-nitrosamines. The optimal extraction conditions for the developed method were as follows: 10.0 g aliquots of the sample were placed in a 50 mL centrifuge tube, followed by the addition of 10 mL acetonitrile and 200 µL internal working standard solutions. After 30 min of freezing treatment, 4 g magnesium sulfate and 1 g sodium chloride were added for dehydration, and the tube was centrifuged at 9000 r/min for 5 min. After vortex centrifugation, 5 mL of the clear supernatant was purified using 150 mg polystyrene divinylbenzene (PLS-A). The purified extracts were dewatered using 1.6 g MgSO4 and 0.4 g NaCl, and then filtered through a 0.22 µm membrane filter unit prior to GC-MS/MS analysis. Temperature-programmed was applied at an initial temperature of 50 ℃. After 0.16 min, the temperature was raised to 220 ℃ at the rate of 900 ℃/min for 5 min. N-Nitrosamines were separated on an HP-Innowax column (30 m×0.25 mm×0.25 µm). Identification and quantification were achieved using an electron impact ion (EI) source in positive ion mode with multiple reaction monitoring (MRM). The internal standard method was used to quantify the N-nitrosamines. Under the optimal conditions, the correlation coefficients of the standard calibration curves were not less than 0.99 in the range of 0.1-50.0 µg/L. The limits of detection were 0.03-0.30 µg/kg (S/N=3), and limits of quantification were 0.15-1.00 µg/kg (S/N=10). At spiked levels of 0.5, 1.0, and 3.0 µg/kg, the average recoveries of N-nitrosamines in spiked samples ranged from 80.4% to 98.5%, with relative standard deviations between 2.41% and 12.50%. This method was used to determine animal derived food products, except N-itrosomethylethylamine and N-nitrosomorpholine, others were founded. The results showed that N-nitrosamines levels in salted aquatic products were generally higher than those of the other samples. The method established in this study is simple to operate, and it does not require any time-consuming distillation extraction. Furthermore, there is minimal consumption of samples and reagents; consequently, the experiment cost is reduced, and the method is environmentally friendly. This method has theoretical and practical significance for the control of N-nitrosamines residues in animal derived foods, establishment of detection standards, and corresponding management measures.

[Preparation of covalent organic framework based on room temperature solution-suspension approach and its application to solid-phase microextraction of pyrethroids in tea].

Pyrethroids (PYs) have been widely used to control pests and prevent diseases in tea gardens. However, with the increasingly stringent pesticide testing standards in the import and export trade of tea, there is an urgent need for methods to detect trace amounts of PYs in tea. In this study, a covalent organic framework (COF) material TpBD with excellent thermal/chemical stability, high porosity, and a large specific surface area was prepared by a room-temperature solution-suspension approach (SSA). TpBD-coated solid phase microextraction (SPME) fibers were fabricated by coating the material on etched stainless-steel fibers by a simple physical coating method. The fibers were used in combination with gas chromatography-tandem mass spectrometry (GC-MS/MS) to establish a highly sensitive method for the detection of PYs. The enrichment factors of this method for cyfluthrin, cypermethrin, flucythrinate, fenvalerate, and deltamethrin were 702-2687. The method showed low LODs (0.1-0.5 ng/L), wide linear ranges (0.2-800 ng/L), good linearities (correlation coefficients (R)≥0.9991) and acceptable repeatabilities (RSD≤11.0%, n=3). Green tea and oolong tea samples were analyzed using the developed method, and trace levels of the five PYs were successfully detected. The recoveries of the spiked PYs in the real green tea and oolong tea samples were in the range of 80.2%-109.5%. Experimental results showed that the established analytical method is suitable for the determination of PY pesticides in tea. Furthermore, the TpBD material was successfully prepared by the SSA method, demonstrating that the method has good universality and excellent potential for the simple synthesis of other COF materials.