[Determination of 14 perfluoroalkyl substances in Chinese mitten crab by multi-plug filtration cleanup coupled with ultra-performance liquid chromatography-tandem mass spectrometry]

Perfluoroalkyl substances (PFASs) have become a new food-safety problem. Dietary intake is a major pathway of human exposure to PFASs. Chinese mitten crab (Eriocheir sinensis) is a high-end aquaculture product popular among consumers in China. Conventional extraction methods for PFASs are cumbersome and time consuming, and result in incomplete purification; thus, this technique does not meet the requirements for PFAS detection. Herein, an analytical strategy was established for the rapid detection of 14 PFASs in Chinese mitten crab based on multi-plug filtration cleanup (m-PFC) and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The carbon-chain length of the 14 PFASs analyzed in this study ranged from 4 to 14, and they are perfluorobutanoic acid (PFBA), perfluoro-n-pentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoDA), perfluorotetradecanoic acid (PFTeDA), perfluoro-1-butane sulfonic acid (PFBS), perfluoro-1-hexane sulfonic acid (PFHxS), perfluoro-1-octane sulfonic acid (PFOS), and perfluoro-1-decanesulfonate (PFDS). The m-PFC column was prepared using carboxy-based multiwalled carbon nanotubes, and used to reduce the interference of sample impurities. The samples were extracted with 5 mL of 0.1% formic acid aqueous solution, 15 mL of acetonitrile and extraction salt (2 g Na2SO4 and 2 g NaCl). The supernatant (10 mL) was purified using the m-PFC column, concentrated to near dryness under nitrogen, and then redissolved in 1 mL of methanol. Finally, the sample solution was filtered through a 0.22 μm polypropylene syringe filter for UPLC-MS/MS analysis. The target analytes were separated using a Shimadzu Shim-pack G1ST-C18 chromatographic column (100 mm×2.1 mm, 2 μm) using methanol (A) and 5 mmol/L ammonium acetate aqueous solution (B) as the mobile phases via gradient elution. The linear gradient program were as follows: 0-0.5 min, 10%A-35%A; 0.5-3 min, 35%A-60%A; 3-5 min, 60%A-100%A; 5-6.5 min, 100%A; 6.5-7 min, 100%A-10%A. The target analytes were analyzed using negative electrospray ionization in multiple-reaction monitoring mode, and quantitative analysis was performed using the internal standard method. In this study, we optimized the mobile-phase system as well as the extraction solvent, time, volume, and salt. The 14 PFASs exhibited good peak shapes and sensitivities when the 5 mmol/L ammonium acetate solution-methanol system was used as the mobile phase. Compared with acetonitrile or methanol alone, the extraction efficiencies of the 14 PFASs were significantly improved when 5 mL of 0.1% formic acid aqueous solution was added, followed by 15 mL of acetonitrile. The extraction efficiencies of the 14 PFASs did not differ significantly when the extraction time was within 3-15 min. The extraction salt (MgSO4, Na2SO4, NaCl, (NH4)2SO4, and Na2SO4+NaCl) significantly affected the extraction efficiencies of the 14 PFASs. The highest extraction efficiencies of the 14 PFASs, which ranged from 47.9% to 121.9%, were obtained when Na2SO4+NaCl was used as the extraction salt. Under the optimal experimental conditions, good linearities (R2=0.998-0.999) were obtained for seven PFASs (PFBS, PFHxA, PFHpA, PFHxS, PFDA, PFDoDA, PFTeDA) at 0.10-100 μg/L, and seven PFASs (PFBA, PFPeA, PFOA, PFOS, PFNA, PFUnDA, PFDS) at 0.50-100 μg/L. The average spiked recoveries for the 14 PFASs in Chinese mitten crabs at three levels ranged from 73.1% to 120%, with relative standard deviations (RSDs) in the range of 1.68%-19.5%(n=6). The limits of detection (LODs) and quantification (LOQs) of the 14 PFASs were in the range of 0.03-0.15 and 0.10-0.50 μg/kg, respectively. The developed method was applied to the analysis of crab samples collected from three farms in Shanghai, and PFASs with total concentrations of 3.52-37.77 μg/kg were detected in all samples. The detection frequencies for PFDA, PFUnDA, PFDoDA, PFTeDA, and PFOS were 100%. PFDA, PFUnDA, PFOS, and PFDoDA were the most abundant congeners, accounting for 31.2%, 30.6%, 15.0%, and 10.9%, respectively, of the 14 PFASs detected. The proposed method is simple, efficient, accurate, and suitable for the rapid analysis of 14 PFASs in Chinese mitten crabs.

[Determination of sixteen antibiotics and four β-agonists in human urine samples using ultra-performance liquid chromatography-tandem mass spectrometry based on high-throughput automatic solid-phase extraction]

An analytical method combining high-throughput automatic solid-phase extraction with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed to determine 16 antibiotics (macrolides, tetracyclines, quinolones, and sulfonamides) and 4 β-agonists (terbutaline, salbutamol, ractopamine, and clenbuterol) in human urine samples. After thawing at room temperature, 1 mL of urine was sampled and the internal standard was added, followed by the addition of 200 μL ammonium acetate buffer and 20 μL β-glucuronidase, and the mixture was incubated at 37 ℃ overnight. Automatic solid-phase extraction was used to extract the target compounds from the urine samples, and the recoveries were compared using different solid-phase extraction 96-well plates (PRiME MCX, Sep-Pak C₁₈, PRiME HLB), types and volumes of rinse solutions and eluents. Satisfactory recoveries of the 20 target compounds were obtained using the Oasis PRiME HLB 96-well plate, with 1.5 mL 10% (v/v) methanol aqueous solution and 2.0 mL methanol as the rinse solution and eluent, respectively. The eluent was concentrated under nitrogen gas at 45 ℃, and the recoveries of the target compounds were compared under different conditions (completely or almost dry, drying to 1 mL, and adding water as a protective agent), and the recovery rate was optimal when water was added as a protective agent. In this study, two types of analytical columns (ACQUITY BEH C₁₈ and ACQUITY HSS T₃) and different gradient elution procedures and mobile phases were compared. The optimal chromatographic effect was realized using an HSS T₃ column (100 mm×3.0 mm, 1.8 μm) and 0.1% (v/v) formic acid aqueous solution-0.1% (v/v) formic acid in acetonitrile as the mobile phase in gradient elution at a flow rate of 0.3 mL/min. Comparing the peaks observed using different proportions of methanol aqueous solution and the initial mobile phase as the injection solvent revealed that 30% (v/v) methanol aqueous solution was the optimal solution in terms of peak shape and signal-to-noise ratio. MS was conducted using positive electrospray ionization (ESI⁺) in multiple reaction monitoring (MRM) mode, and the MS parameters were optimized, including the curtain (CUR) and collision gases (CAD). The standard curve obtained using this method exhibited a good linearity (correlation coefficient>0.997), and the respective limits of detection and quantification were 0.02-0.12 ng/mL and 0.06-0.41 ng/mL. At spiked levels of 0.25, 2.5, and 12.5 ng/mL, the recoveries were in the range of 81.7%-120.0% (except that of tetracycline), the intra- and inter-day RSDs (n=6) were 1.1%-11.0% and 1.2%-13.0%, respectively. Azithromycin, trimethoprim, terbutaline, salbutamol, ractopamine, and clenbuterol displayed moderate matrix effects, but all targets exhibited weak matrix effects after correction using the isotope internal standard. To evaluate the accuracy of this method, BCR-503 (containing salbutamol and clenbuterol) and internal quality control samples were used and the concentrations of salbutamol and clenbuterol were within the reference ranges. Additionally, the mean concentrations of the 20 target compounds of two different internal quality control samples after 7 measurements were in the ranges of 0.44-0.59 ng/mL (0.5 ng/mL) and 1.72-2.16 ng/mL (2.0 ng/mL), respectively, which were satisfactory. In this study, the analytical method employed automatic sample pretreatment with a 96-well solid-phase extraction plate, and the detection efficiency was considerably improved. This method displays the advantages of simple operation, ideal recovery, a high sensitivity and weak matrix effect, which satisfies the requirements for the simultaneous determination of 16 antibiotics and 4 β-agonists in human urine samples. This study provides a crucial method for use in monitoring antibiotics and β-agonists in human urine and studying their exposure characteristics and health risks.

[Development of a multi-residue detection method for 27 typical pharmaceuticals and personal-care products in plants and analysis of their migration patterns in sprouts]

An analytical method based on ultra-performance liquid chromatography-tandem mass spectrometry was developed for the simultaneous determination of 27 pharmaceutical and personal-care product (PPCP) residues in plants. The enrichment and cleanup of PPCPs in plants were achieved using an HLB extraction column, and the separation was performed on a BEH C18 column (100 mm×2.1 mm, 1.7 μm) with 0.1% formic acid water-acetonitrile as the mobile phase via gradient elution. PPCPs were detected with electrospray ionization mass spectrometry in positive-ion multiple-reaction monitoring (MRM) mode. The limits of detection and quantification of the 27 PPCPs in plants were 0.01-0.30 μg/kg and 0.03-0.98 μg/kg, respectively. Good linearities were observed with coefficients of determination (r2) >0.99. The spiked recoveries were between 80.8% and 122.3% with relative standard deviations (RSDs) between 1.0% and 9.9%. The method was subsequently used to study sprouts grown in different concentrations of PPCPs. A total of 10 PPCPs were detected in sprouts grown in medium with a low concentration PPCPs, 13 PPCPs were detected in sprouts grown in medium with a moderate concentration of PPCPs, and 19 PPCPs were detected in sprouts grown in medium with a high concentration of PPCPs. These results showed that plants grown in water bodies contaminated with PPCPs or irrigated with water contaminated with PPCPs absorbed and accumulated these substances and that the amount and type of PPCPs absorbed by plants were closely related to the levels of PPCPs in the external environment. Analysis of the contents of PPCPs in different plant tissues revealed a general distribution of root>stem>leaf. Haemosibutramine showed a tissue distribution of leaf>stem>root, while glibenclamide showed a distribution of root>leaf>stem; these results revealed differences in the distribution of PPCPs in plants. Calculation of the transfer factor (TF) of the PPCPs in plants demonstrated significant differences in the transferability of different PPCPs, with TF=2.34 for haemosibutramine and TF=1.25 for chlorosibutramine. The results showed that among the drugs that migrated in plants, haemonosibutramine and chlorosibutramine had the strongest migration ability in sprouts, followed by nicardipine and chlorpheniramine maleate, and amantadine, N-monodesmethyl sibutramine, carbamazepine and flumequine had the weakest migration ability. Once absorbed, these compounds were transferred to the stems and/or leaves, where they accumulate and cause potential harm by contaminating other plant organs. Therefore, PPCPs such as homosibutramine and chlorosibutramine, which easily migrate in plants, should be given extra attention in future studies. The method is simple in pre-treatment, sensitive and accurate, and can be widely applied to the detection of PPCP residues in plant samples.

[Determination of 18 caine anesthetics in animal meat using solid phase extraction combined with ultra-performance liquid chromatography-tandem mass spectrometry]

Because of the widespread application of anesthetic drugs in the fields of animal breeding and transportation, demand for the rapid, sensitive detection of anesthetic drugs in animal meat is increasing. The complex animal meat matrix contains various interfering substances, such as proteins, fats, and phospholipids, along with anesthetic drug residues at very low concentrations. Therefore, adopting appropriate pretreatment methods is necessary to improve the sensitivity of detection. In this study, a rapid, accurate analytical method based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and solid phase extraction (SPE) was established to determine the contents of 18 caines in animal meat. The MS parameters, such as the collision energies of 18 caines, were optimized. Furthermore, the chromatographic separation conditions and response intensities of the caine in different mobile phases were compared. The effects of different pretreatment conditions on the extraction efficiencies of the 18 caines in meat samples and those of different purification conditions, such as extraction solvent, SPE column, and dimethylsulfoxide (DMSO) dosage, on their recoveries were investigated. Combined with the external standard method, the 18 caines in meat were successfully quantified. Sample pretreatment is a three-step process. First, in ultrasound-assisted extraction, 2.0 g samples were added to 2.0 mL water and extracted using 10 mL 0.1% (v/v) formic acid in acetonitrile under ultrasound conditions for 10 min. SPE was then performed using an Oasis PRIME HLB column. Finally, DMSO-assisted concentration was employed: the organic layer was collected and dried at 40 ℃ under a stream of N₂ gas with the addition of 100 μL DMSO. Acetonitrile-water (1∶9, v/v) was added to the residue to yield a final volume of 1.0 mL for use in UPLC-MS/MS. The 18 caines were separated using an HSS T₃ (100 mm×2.1 mm, 1.8 μm) column with 0.1% (v/v) formic acid in water (containing 0.02 mmol/L ammonium acetate) and methanol as mobile phases. Samples were detected using an electrospray ion source (ESI) in the positive ion and multiple reaction monitoring (MRM) modes during UPLC-MS/MS. Under the optimized conditions, the 18 target caine anesthetics displayed good linearities in the range of 1.00-50.0 μg/L, and the correlation coefficients (R²) were >0.999. The respective limits of detection (LODs) and quantification (LOQs) were 0.2-0.5 μg/kg, and 0.6-1.5 μg/kg. In pork, beef, and mutton samples, the recoveries obtained at three spiked levels were 83.4%-100.4% with relative standard deviations (RSDs) of 3.1%-8.5%. This simple, rapid, sensitive method may be applied in the detection of 18 caine anesthetics in animal meat and may provide technical support to the food safety department in China in monitoring the residues of caine anesthetics in animal meat.

[Determination of phenoxyacetic herbicides, metabolites of organophosphorus and pyrethroid pesticides in human urine using solid phase extraction coupled with ultra-performance liquid chromatography-tandem mass spectrometry]

Pesticides are widely used in most agricultural areas to protect food crops but adversely affect ecosystems and human beings. Pesticides have attracted great public concern due to their toxic properties and ubiquitous occurrence in the environment. China is one of the largest users and producers of pesticides globally. However, limited data are available on pesticide exposure in humans, which warrants a method for quantification of pesticides in human samples. In the present study, we validated and developed a comprehensive and sensitive method for the quantification of two phenoxyacetic herbicides, two metabolites of organophosphorus pesticides and four metabolites of pyrethroid pesticides in human urine using 96-well plate solid phase extraction (SPE) coupled with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). For this purpose, a systematic optimization of the chromatographic separation conditions and MS/MS parameters was conducted. Six solvents were optimized for the extraction and clean-up of human urine samples. The targeted compounds in the human urine samples were well separated within 16 min in one analytical run. A 1 mL aliquot of human urine sample was mixed with 0.5 mL sodium acetate buffer (0.2 mol/L) and hydrolyzed by β-glucuronidase enzyme at 37 ℃ overnight. The eight targeted analytes were extracted and cleaned using an Oasis HLB 96-well solid phase plate and eluted with methanol. The separation of the eight target analytes was performed on a UPLC Acquity BEH C₁₈ column (150 mm×2.1 mm, 1.7 μm) with gradient elution using 0.1% (v/v) acetic acid in acetonitrile and 0.1% (v/v) acetic acid in water. The analytes were identified using the multiple reaction monitoring (MRM) mode under negative electrospray ionization (ESI^-) and quantified by isotope-labelled analogs. Para-nitrophenol (PNP), 3,5,6-tricholor-2-pyridinol (TCPY) and cis-dichlorovinyl-dimethylcyclopropane carboxylic acid (cis-DCCA) exhibited good linearities ranging from 0.2 to 100 μg/L, and 3-phenoxy benzoic acid (3-PBA), 4-fluoro-3-phenoxy benzoic acid (4F-3PBA), 2,4-dicholorphenoxyacetic acid (2,4-D), trans-dichlorovinyl-dimethylcyclopropane carboxylic acid (trans-DCCA) and 2,4,5-tricholorphenoxyacetic acid (2,4,5-T) showed linearity ranging from 0.1 to 100 μg/L with correlation coefficients all above 0.9993. Method detection limits (MDLs) and method quantification limits (MQLs) of targeted compounds were in the range of 0.02 to 0.07 μg/L and 0.08 to 0.2 μg/L, respectively. The spiked recoveries of target compounds at three levels of 0.5, 5 and 40 μg/L were 91.1% to 110.5%. The inter- and intra-day precisions of targeted analytes were 2.9% to 7.8% and 6.2% to 10%, respectively. This method was applied to the analysis of 214 human urine samples across China. The results showed that all the targeted analytes, except 2,4,5-T, were detected in human urine. The detection rates of TCPY, PNP, 3-PBA, 4F-3PBA, trans-DCCA, cis-DCCA, and 2,4-D were 98.1%, 99.1%, 94.4%, 2.80%, 99.1%, 63.1% and 94.4%, respectively. The median concentration of targeted analytes in a decreasing order were: 2.0 μg/L (TCPY), 1.8 μg/L (PNP), 0.99 μg/L (trans-DCCA), 0.81 μg/L (3-PBA), 0.44 μg/L (cis-DCCA), 0.35 μg/L (2,4-D) and below MDLs (4F-3PBA ). For the first time, we developed a method to extract and purify specific biomarkers of pesticides from human samples based on offline 96-well SPE. This method has the advantages of simple operation, high sensitivity, and high accuracy. Moreover, up to 96 human urine samples were analyzed in one batch. It is suitable for the determination of eight specific pesticides and their metabolites in large sample sizes.

Detection of Phosphatidylethanol in Whole Blood by UPLC-MS/MS

OBJECTIVES

To establish the ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method to detect ethanol metabolites phosphatidylethanol (PEth) in whole blood.

METHODS

An appropriate amount of aqueous solution including 1% formic acid was added to 100 μL whole blood, the protein was precipitated with acetone, centrifuged and the supernatant was purified and enriched by using Bond Elut Certify column. The eluent was redissolved with 1/1 isopropanol/acetonitrile (v/v) solution after nitrogen blowing and then tested by UPLC-MS/MS. Selective reaction monitoring scanning was carried out in negative ionization mode, and quantitative analysis was performed by external standard method.

RESULTS

PEth showed a linear relationship over the concentration range of 1-160 ng/mL in whole blood (r=0.999 9) with peak area. The detection limit was 0.2 ng/mL, the quantification limit was 1 ng/mL, the recovery rate was 97.43%-103.61%, the accuracy was 0.99%-1.77%, the intra-day precision was 0.4%-2.4%, and the inter-day precision was 1.1%-3.3%, and the matrix effect was 91.00%-99.55%. PEth was not detected in the in vitro blood samples supplemented with ethanol. PEth was detected positive in three drunk driving cases, and the concentration were 195.49, 83.67 and 876.12 ng/mL, respectively.

CONCLUSIONS

The established method has high sensitivity and specificity and the analysis results are accurate. It is suitable for the qualitative and quantitative analysis of PEth in whole blood.

[Determination of 44 foodborne stimulants and 6 progestogens in meat by QuEChERS and ultra-performance liquid chromatography-tandem mass spectrometry]

To ensure the success of large-scale sporting events, prevent the contamination of food by prohibited substances, and evaluate the risk of foodborne stimulants and other hormones in food, it is necessary to establish a high-throughput, rapid, and accurate detection method for foodborne stimulants and other hormones. In this study, a QuEChERS method is proposed for the simultaneous determination of 44 foodborne stimulants and 6 progestogens using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The analyzed foodborne stimulants include 19 β2-agonists, 3 β-blockers, 11 anabolic agents, 8 glucocorticoids, and 3 diuretics. A meat sample was crushed and homogenized, following which the internal standard was added. Subsequently, the sample was shaken and extracted with water and an acetonitrile solution containing 0.5% acetic acid, then dehydrated and centrifuged with sodium chloride and anhydrous magnesium sulfate. The supernatant was purified by PSA, C18, neutral alumina, and anhydrous magnesium sulfate. It was then dried with nitrogen and concentrated. The concentrated extracts were separated using an ACQUITY BEH C18 column (100 mm×2.1 mm, 1.7 μm) with gradient elution using 0.1% formic acid-5 mmol/L ammonium acetate solution and methanol as mobile phases. The target compounds were detected by ultra-performance liquid chromatography-tandem mass spectrometry with electrospray ionization and positive ion scanning (ESI+) in the multiple reaction monitoring (MRM) mode, and quantified by the internal standard method. The linear ranges of β2-agonists and β-blockers were 0.1-20 μg/L, the linear ranges of glucocorticoids were 0.5-200 μg/L, and those of the others were approximately 0.2-50 μg/L. The linear relationships of 50 compounds were good, with correlation coefficients >0.99 in the linear ranges, and limits of quantification (LOQs) in the range of 0.1-0.4 μg/kg. The recoveries of the 50 target compounds spiked in chicken, pork, beef, lamb samples at three levels ranged from 50.3% to 119.9%, while the relative standard deviations (RSDs, n=6) ranged from 0.42% to 15.1%. Nine meat samples (including 3 beef, 3 pork, 2 chicken, and duck samples) were tested by this method and the national standard method (GB/T 21981-2008). The t test was used for statistical analysis of the hydrocortisone and cortisone contents, and no significant difference was found between the results obtained by the two methods. The developed method was used to analyze 12 beef samples from a farm. In all, 4 compounds were detected, while the other 46 were not detected. The content ranges and detection rates of the compounds were as follows: hydrocortisone: 3.3-22.6 μg/kg, 100%; cortisone: 1.5-2.1 μg/kg, 67%; androstenedione: 0.7-1.2 μg/kg, 17%; and testosterone: 0.6-1.5 μg/kg, 42%. In conclusion, the proposed method is simple, accurate, and sensitive, and hence, is suitable for the detection of foodborne stimulants and progestogens in different kinds of raw meat.

[Pollution Characteristics and Health Risk Assessment of Perfluorinated Compounds in PM2.5 in Zhejiang Province]

As typical new pollutants, perfluorinated compounds (PFCs) have been widely concerned by environmental workers in recent years. This study was carried out to investigate the pollution characteristics of perfluorinated compounds in atmospheric particulate matter (PM_2.5) in Zhejiang Province. The chemical extraction of PM_2.5 was performed using the accelerated solvent extraction (ASE) method with mixed dichloromethane and acetone (2:1). The chemical analysis was implemented by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results showed that the daily average concentration of the sum of 12 PFCs (Σ₁₂ PFCs) ranged from 131.63 pg·m^-3 to 578.53 pg·m^-3, which was slightly higher in winter compared to that in autumn. The concentrations of perfluorosulfonic acids (PFSAs) were much lower than those of perfluorocarboxylic acids (PFCAs). PFOS was the primary contaminant among PFASs, with an average concentration of 12.90 pg·m^-3. The content of PFCAs exhibited a trend of PFOA>PFHxA>PFHpA, and the detection rate of long-chain PFCs was much lower than that of short-chain PFCs. The hysplit-4 model was used to calculate the QZ air mass transport trajectory. The results indicated that the backward trajectory of this point was significantly different along time, and the source of air mass rarely affected the concentration. The forward trajectory confirmed that PFCs can be transmitted over long distances in the atmosphere in a short time. The correlation coefficient between PFUdA and PFTeDA was evaluated to be 0.68, and that between PFHxS and PFOS was 0.66, suggesting the same sources of these chemicals. The content of PFCs was positively correlated with PM_2.5, indicating that people might suffer from higher health risks on haze days. The risk quotient estimation implied no health risk of PFCs in PM_2.5 in Zhejiang Province.

[Determination of seven Alternaria toxins in infant milk powder by solid phase extraction coupled with ultra-performance liquid chromatography-tandem mass spectrometry]

Alternaria toxin is a general term for a class of toxic metabolites produced by Alternaria, which widely exists in soil, grain, vegetables, and fruits. This mycotoxin is extremely harmful to human health. It is well known that infant milk powder containing vegetable oil is easily contaminated by Alternaria alternata. Alternaria toxins have thus become an increasingly important focus in food. Rapid and accurate detection of Alternaria toxin residues in food is of great significance for food safety. This requires pretreatment to purify the target toxins and maximize the accuracy and precision of the analysis. In this study, a rapid method based on online solid phase extraction/purification and ultra-performance liquid chromatography-tandem mass spectrometry (online SPE UPLC MS/MS) was established to detect seven Alternaria toxins (alternariol monomethyl ether, altenuene, tenuazonic acid, alternariol, tentoxin, altenusin, and altertoxin Ⅰ) in infant milk powder. First, the mass spectrometry and chromatographic conditions were optimized. A BEH-C18 column (50 mm×2.1 mm, 1.7 μm) was selected, with 0.1% formic acid aqueous solution-acetonitrile as the mobile phase. Then, the extraction conditions (extraction agent ratio and extraction method) and the solid phase extraction process (extraction column, type and volume of the eluent, and pH of the sample loading solution) were optimized. One gram of milk powder (accurate to 0.01 g) was weighed into a 50 mL tip and bottom plug centrifuge tube. Acetonitrile-water (84∶16, v/v) was set as the extraction agent for the first two cycles, and acetonitrile-methanol-water (45∶10∶45, v/v/v) was set as the third extraction agent. Horizontal shaking for 30 min was the best extraction method. The sample was centrifuged at 9500 r/min for 10 min, and the supernatant extracted many times was mixed and blown with nitrogen at 40 ℃. The sample was redissolved in first-order water (pH 5.5), purified on an HLB column, and successively activated with 6 mL methanol and 6 mL first-order water (pH 5.5). The solution was then loaded onto the column, and the SPE was adjusted to ensure that the water sample flowed through the column at the rate of 1 mL/min so that the column did not dry up during the analysis process before the end of sample loading. The column was rinsed with 12 mL of first-order water. After leaching, the negative pressure filtration was continued for approximately 5 min, followed by elution with 10 mL methanol, and the eluted solution was directly tested after passing through a 0.22 μm filter membrane, without concentration. The analytes were determined by electrospray ionization (ESI) with alternating positive and negative ions. Under the optimal analysis conditions, the linear relationships of the seven Alternaria toxins were good in the mass concentration range of 0.5-200 μg/L, with coefficients of determination (R2)>0.9903. The limits of detection and limits of quantification were 0.15-0.64 μg/kg and 0.54-2.24 μg/kg, respectively. The recoveries of the seven Alternaria toxins were 79.1%-114.3%, and the relative standard deviations were less than 8.87% at different concentrations. The method was applied to the determination and analysis of 60 samples of infant milk powder, and the results showed that no toxin was found in stage one or stage two of the milk powder. Only one sample of the stage three of milk powder was detected, which was tentoxin, and the content was 4.97 μg/kg. The developed method is accurate, rapid, simple, sensitive, repeatable, and stable. It can be used for the practical determination of seven Alternaria toxins in infant milk powder.

[Simultaneous determination of beauvericin and four enniatins in eggs by ultra-performance liquid chromatography-tandem mass spectrometry coupled with cold-induced liquid-liquid extraction and dispersive solid phase extraction]

新型生物毒素白僵菌素(BEA)和恩镰孢菌素(ENNs)是由镰刀菌种产生的有毒代谢产物,主要污染谷物及其制品,会威胁人类健康,因此受到人们越来越多的关注。该工作建立了冷诱导液液萃取-分散固相萃取净化-超高效液相色谱-串联质谱法(CI-LLE-DSPE-UPLC-MS/MS)同时测定鸡蛋中白僵菌素和4种恩镰孢菌素残留的分析方法。以乙腈-水-乙酸(79:20:1, v/v/v)为提取溶剂,采用冷诱导液液萃取与分散固相萃取净化相结合的方法进行样品处理,同时,对影响待测物提取与净化效率的提取溶剂、冷冻萃取温度与时间、净化剂用量等因素和色谱条件进行了优化。样品经20 mL提取液涡旋提取20 min,放入-40 ℃冰箱静置30 min后,取2 mL上层溶液经70 mg C18粉末净化,离心,上清液于40 ℃浓缩至近干,残留物用1 mL 80%(v/v)乙腈水溶液溶解,进样分析。以乙腈与5 mmol/L甲酸铵溶液作为流动相进行梯度洗脱,经ACQUITY UPLC BEH C18色谱柱(100 mm×2.1 mm, 1.7 μm)分离,采用ESI⁺电离,在多反应监测模式下采集,白僵菌素采用稳定同位素内标法定量,4种恩镰孢菌素采用基质匹配曲线外标法定量。结果表明,5种待测物在0.1~50.0 μg/L范围内线性关系良好,相关系数(r²)为0.9983~0.9997,该方法的检出限(LOD)为0.05~0.15 μg/kg,定量限(LOQ)为0.20~0.50 μg/kg。以阴性鸡蛋样品为基质,在低、中、高3个浓度水平(0.5、5.0、25.0 μg/kg)下进行加标试验考察方法的准确度与精密度,各待测物的平均回收率为81.1%~106%,相对标准偏差(RSD)为0.27%~9.79%。采用所建立的方法对农村散养鸡蛋与市售鸡蛋进行检测,结果表明,BEA在散养鸡蛋的检出率为30.4%, 4种ENNs均未被检出。该方法灵敏度高,稳定性好,回收率高,定量准确,简单易操作,适用于禽蛋食品中白僵菌素与恩镰孢菌素的同时快速测定。

[Determination of eight environmental phenols in human urine samples by high-throughput solid-phase extraction-ultra-performance liquid chromatography-tandem mass spectrometry]

A method combining 96-well plate solid-phase extraction with ultra-performance liquid chromatography-tandem mass spectrometry (96-well SPE LC-MS/MS) was developed for the simultaneous determination of eight environmental phenols in urine samples. The samples included seven bisphenol compounds and triclosan. The urine samples were thawed to room temperature, and the target analytes were deconjugated by β -glucuronidase/aryl-sulfatase in ammonium acetate buffer solution at 37℃ overnight. Then, the effects of three kinds of 96-well solid-phase extraction plates and different elution conditions on the purification of the urine samples and the environmental phenol recoveries were compared. The best purification effect was achieved on Oasis HLB 96-well plate (60 mg) solid phase extraction, using 30% (v/v) acetonitrile aqueous solution as the rinse solution. The target analytes were then eluted by methanol solution and evaporated to dryness using a nitrogen blower. After reconstruction with 0.5 mL methanol/water (1:1, v/v) solution, the target compounds were detected by UPLC-MS/MS. To achieve better chromatographic separation, two kinds of analytical columns (C₁₈ and T3) and different types of mobile phases (methanol and acetonitrile as the organic phase) were also compared. The best chromatographic effect was achieved when the treated samples were separated on a C₁₈ column (100 mm×2.1 mm, 1.7 μm) using acetonitrile/water as the mobile phase at a flow rate of 0.3 mL/min. Mass spectra were recorded by negative electrospray ionization under the multiple reaction monitoring (MRM) mode. The sample matrix effect was also evaluated. The absolute matrix effects of bisphenol A, bisphenol F, bisphenol S, bisphenol B, and bisphenol AF were in the range of 3.47% to 15.32%. Since the above mentioned matrix effect was weak, there was no need for compensation measures. On the contrary, tetrachlorobisphenol A, tetrabromobisphenol A, and triclosan showed an absolute matrix effect of 49.58% (moderate), 71.99% (strong), and 86.93% (strong), thus necessitating compensation measures. Therefore, this strategy uses a one-to-one corresponding isotope internal standard method to offset the matrix effect. Six different urine samples were used to evaluate the relative matrix effect. The relative standard deviations (RSDs) of the eight corresponding internal standard peak areas were 3.63%-9.06%, indicating that the relative matrix effect was stable. Under the optimized conditions, linearity ranges were 0.50-50 μg/L for bisphenol A and bisphenol AF; 0.05-50 μg/L for tetrachlorobisphenol A and bisphenol S; 0.01-50 μg/L for bisphenol F and tetrabromobisphenol A; 1.00-50 μg/L for bisphenol B; and 5.00-200 μg/L for triclosan. The correlation coefficients were all greater than 0.9995. At spiked levels of 2.5, 5, and 25 μg/L, the average recovery ratios of the eight target analytes were 81.01%-118.84%, while the intra-day and inter-day precisions were 0.38%-19.41% and 2.54%-17.83%, respectively. The limits of detection (LOD) were 0.002-1.09 μg/L, and the limits of quantitation (LOQ) were 0.007-3.63 μg/L. This method was successfully applied to the determination of the eight environmental phenols in 64 urine samples collected from Beijing area between 2019 and 2020. All the target environmental phenols were detected, except for bisphenol B and bisphenol AF. Bisphenol A and bisphenol S showed the highest detection rates of 100% and 96.9%, respectively. The detection rates of triclosan, tetrabromobisphenol A, tetrachlorobisphenol A, and bisphenol F were 57.8%, 46.9%, 23.4%, and 21.9%, respectively. The medium values of urinary concentration followed the order 1.44 μg/L(triclosan), 0.69 μg/L(bisphenol A), 0.086 μg/L (bisphenol S), 0.0032 μg/L (tetrabromobisphenol A), 0.00050 μg/L (tetrachlorobisphenol A), 0.00 μg/L (bisphenol F, bisphenol B, and bisphenol AF). The aforementioned results imply that the widespread environmental phenolic exposure of Beijing residents is worthy of attention. Compared with traditional solid-phase extraction methods, the method reported in this paper is time-saving, effective, and suitable for the simultaneous analysis of large quantities of samples; moreover, the small sample and organic solvent consumption make this method more environment- and operator-friendly.

[Determination of four antipyretic and analgesic drugs in water by solid-phase extraction coupled ultra-performance liquid chromatography-tandem mass spectrometry]

The widespread use of pharmaceutical and personal care products (PPCPs), including antipyretic and analgesic drugs, in the last two decades had led to the existence of PPCP residues in the environment, thus raising concerns about their pseudo-persistent nature and potential threat to human health. Generally, most of the detected contaminants are present at low levels (ranging from ng/L to μg/L) in environmental water. Therefore, advanced analytical methodologies are crucial to monitor the occurrence and distribution of antipyretic and analgesic drugs in environmental water. However, trace analysis of environmental pollutants is always challenging because it is necessary to extract analytes present in the sample at ultralow levels from complex environmental matrices. Therefore, an appropriate sample pretreatment is necessary to enrich the target compounds. Conventional solid-phase extraction materials show poor efficiency for the enrichment of antipyretic and analgesic drugs. We herein report a hydrophilic and lipophilic amphiphilic porous polymeric material GCHM (Guochuang hydrophilic material). GCHM was successfully prepared by a stepwise emulsification and micellization process using N-vinyl-2-pyrrolidone (NVP) and divinylbenzene (DVB) as raw materials. An ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the determination of four antipyretic and analgesic drugs in water using our solid-phase extraction (SPE) column. The water samples were extracted and purified by the GCHM solid-phase extraction column, and then analyzed by UPLC-MS/MS. Gradient elution was carried out with 0.1% formic acid aqueous solution and acetonitrile as the mobile phase. The target analytes were separated on an ACQUITY UPLC HSS T3 column (100 mm×2.1 mm, 1.8 μm), and multiple reaction monitoring (MRM) was conducted in the positive electrospray ionization mode. The isotope internal standard method was used for quantitative correction. Comparison of the enrichment efficiencies of Oasis HLB, Bond Elut Plexa, and GCHM revealed that GCHM showed the best performance. Different pH values affecting the enrichment efficiency of the GCHM SPE column were optimized, and the matrix effect was evaluated. The results showed that the four target analytes gave the best enrichment effect on the SPE column at pH 7, and the matrix effect for each substance was between 82.8% and 102.2%, indicating obvious matrix removal after the water sample was purified by the GCHM SPE column. Good correlation coefficients (r) greater than 0.995 were observed for all the target compounds in the range of 1-100 μg/L. The method limits of quantitation (S/N=10) ranged from 1 ng/L to 5 ng/L. The corrected recoveries were 85.6% to 106.4%, and the relative standard deviations (RSD) were under 5.6%. The GCHM solid-phase extraction column is inexpensive and efficient, being suitable for the detection of the four antipyretic and analgesic drugs in water. Subsequently, the occurrence of these selected antipyretic and analgesic drugs in water samples from Shanghai, Jiangsu, and Guangdong provinces were studied. The GCHM column has potential advantages over the commercial imported SPE column and is worthy of widespread application. This column can also aid the enrichment and purification of other compounds with similar structures or properties in water.

[Simultaneous determination of 37 mycotoxins in grain and animal feed by impurity adsorption purification coupled with ultra-performance liquid chromatography-tandem mass spectrometry]

A rapid method based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for the simultaneous determination of 37 mycotoxins having various physicochemical properties in grain and animal feed samples. The 37 analytes were extracted from ground samples with acetonitrile-water-formic acid (84:15.9:0.1, v/v/v) by 20 min vibration, and purified using a commercial MLJ-1 pass-through solid-phase extraction (SPE) clean-up cartridge. The analytes were then separated on a reversed-phase BEH RP18 column by a gradient elution program with 0.1 mmol/L ammonium acetate (containing 0.1% (v/v) formic acid) aqueous solution and 0.1% (v/v) formic acid methanol solution as mobile phases. The separated analytes were detected by MS/MS in the multiple reaction monitoring (MRM) mode via ESI+/- ionization. The results showed that the purification was completed in 1 min and that the 37 analytes could be separated on the chromatographic column in 15 min. The 37 mycotoxins showed a linear relationship within their respective linear ranges, and the correlation coefficients of the matrix-matched calibration curves were greater than 0.98. The average recoveries at four spiked levels (limit of quantification (LOQ), LOQ×5, LOQ×10, LOQ×25) for all the targets except fumonisins ranged from 80% to 120%, with the relative standard deviations (RSDs) lower than 20% (n=6). The limits of quantification (LOQs) for all the analytes were between 2 and 40 μg/kg. The proposed method is simple, fast, and accurate, thus being suitable for detecting multiple mycotoxins in grain and animal feed samples.

[Determination of myclobutanil enantiomers in wheat and its processed products by ultraperformance liquid chromatography-tandem mass spectrometry based on a chiral stationary phase]

A valid method based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) with a chiral stationary phase was established for the determination of myclobutanil enantiomer residue in wheat grain and its processed products (flour, bran, pasta, steamed bun, noodle, and cooking water). The wheat grain and processed product samples were extracted with acetonitrile and purified with primary secondary amine (PSA) and C18. The enantiomers of myclobutanil were separated by Chiral column Lux Cellulose-1 (150 mm×2.0 mm, 3 μm, Phenomenex). The column temperature, sample volume injected, and flow rate were 30 ℃, 5 μL, and 0.25 mL/min, respectively. The mobile phase consisted of phase A (25%), water with 0.1% formic acid and 4 mM ammonium acetate, and phase B (75%), methanol with 0.1% formic acid and 4 mM ammonium acetate. A Waters Xevo TQ-S Micro MS/MS system (Waters, USA) was used for mass spectrometric analysis. An electrospray ionization (ESI) source operating in the positive ionization mode. MS analyses were performed in the multiple reaction monitoring (MRM) mode. The qualitative ions of myclobutanil were m/z 288.9/69.9 and 288.9/124.9, and the quantitative ion of myclobutanil was m/z 288.9/69.9. The source voltage was 3000 V, and the desolvation temperature was 400 ℃. The desolvation gas flow was 800 L/h, and the source temperature was 150 ℃. The matrix effect of wheat grains and their processed products on the determination of myclobutanil enantiomers by UPLC-MS/MS was investigated. S-(+)-myclobutanil and R-(-)-myclobutanil had a mid signal suppression effect on wheat grain, bran, pasta, steamed bun, and noodle, while S-(+)-myclobutanil and R-(-)-myclobutanil had a mid signal enhancement effect on flour and cooking water. Finally, the matrix-matched calibration method was effective in all matrices and was selected for the quantification of the myclobutanil enantiomer residue in the samples. The results showed that the two enantiomers of myclobutanil were well separated by this method. The first and second eluted enantiomers were S-(+)-myclobutanil and R-(-)-myclobutanil, respectively, with the corresponding retention times being 4.34 min and 5.13 min. The limits of detection (LOD) and limits of quantification (LOQ) of S-(+)-myclobutanil and R-(-)-myclobutanil in wheat and its processed products were 0.2 μg/kg and 0.5 μg/kg, respectively. In the linear range of 0.5-25 μg/L, the peak areas of the myclobutanil enantiomers showed a good linear relationship with the concentration, and the R2 values were all greater than 0.99. At fortification levels of 5, 50, and 100 μg/kg (enantiomer concentration), the average recoveries of S-(+)-myclobutanil in wheat grain and its processed products ranged from 82% to 110%, with RSDs between 0.9% and 6.8%. The average recoveries of R-(-)-myclobutanil in wheat grain and its processed products ranged from 80% to 109%, with RSDs between 0.9% and 6.8%. This method fulfils the requirements for pesticide residue analysis. The established method was applied to analyze five flour samples, two noodle samples, and two steamed bread samples. The results showed that S-(+)-myclobutanil and R-(-)-myclobutanil enantiomers were not detected in the samples. In this study, methods for the enantiomeric separation and residue analysis of myclobutanil in wheat were evaluated at the enantiomeric level, which enriched the methods of enantiomeric separation and residue analysis of chiral pesticide myclobutanil enantiomers in raw agricultural product (wheat grain) and its processed foods. This method is effective for the residue analysis of chiral pesticide myclobutanil enantiomers in raw agricultural commodities and its processed products.

[Determination of ethylenethiourea residues in tea using precolumn derivatization with ultra-performance liquid chromatography-tandem mass spectrometry]

A method based on precolumn derivatization along with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for the determination of ethylenethiourea residues in tea. The sample was extracted using acetonitrile; the extracting solution was purified by matrix-dispersed solid phase extraction and precolumn derivatization using 9-fluorenylmethyl chloroformate (FMOC-CL). The UPLC separation was carried out on an Acquity BEH C18 column (100 mm×2.1 mm, 1.7 μm) and quantified using the isotope internal standard method. The mobile phase was 0.1% (v/v) formic acid and acetonitrile. For tea samples, the detection limit of this method was 1.3 μg/kg and the limit of quantitation was 4.2 μg/kg. The recoveries were in the range 97.7%-107.5% with relative standard deviation (RSD) of 2.1%-10.0% (n=6). The linear correlation coefficient (r) was 0.9993 over the concentration range 1.0-203.4 μg/L. This method showed high sensitivity, good reproducibility, and qualitative and quantitative accuracy, and could be suitable for the detection of ethylenethiourea residues in tea.

[Rapid determination of benzidine, picric acid, carbaryl, atrazine, and deltamethrin in surface water by ultra-performance liquid chromatography-tandem mass spectrometry]

A method requiring no pre-treatment steps other than filtration, using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), has been developed and applied for the rapid determination of benzidine, picric acid, carbaryl, atrazine, and deltamethrin residues in surface water. Water samples were filtered with a 0.2-μ m syringe filter for particle removal and injected directly into the UPLC instrument. The separation was performed on a Waters Acquity UPLC HSS T₃ column utilizing a gradient elution program of methanol (containing 2 mmol/L ammonium acetate) and water (containing 2 mmol/L ammonium acetate) as the mobile phases at a flow rate of 0.4 mL/min. The detection was accomplished by multiple-reaction monitoring scanning in positive/negative ion-switching electrospray ionization mode. Good linearity was observed in the range 0.10-10.0 μ g/L or 1.00-100 μ g/L for different targets with correlation coefficients of 0.996-0.999. The limits of detection (LODs) were 0.01-0.22 μ g/L. The recoveries ranged between 81.4% and 113% at three spiked levels with relative standard deviations (n=6) between 0.84% and 14.0%. The developed method was applied to the analysis of surface waters (river water and reservoir water) from Hangzhou; atrazine and deltamethrin were detected in part of the analyzed samples. This proposed method was characterized by high sensitivity and precision, extensive analytical range, and a high analytical rate, and showed suitability for the analysis of the five named pollutants in surface water.

[Determination of migration of perfluorooctanoic acid and perfluorooctane sulfonic acid from food contact materials by ionic liquid-based dispersive liquid-liquid microextraction and ultra-performance liquid chromatography-tandem mass spectrometry]

A new method was developed to determine the migration of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) from food contact materials (FCMs) using ionic liquid-based dispersive liquid-liquid microextraction (IL-DLLME) coupled with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). FCM samples were soaked in three food simulants of water, 10% (v/v) aqueous ethanol solution, and 4% (v/v) acetic acid solution for the migration test, and then the migration liquid was extracted and enriched using the IL-DLLME. The key parameters in terms of the type and volume of extractant, vortex time, NaCl concentration, and the speed and time of centrifugation were investigated. The analytes were separated on a Waters ACQUITY UPLC BEH Shield RP18 column (50 mm×2.1 mm, 1.7 μm), eluted by gradient with acetonitrile and water, and quantified by electrospray ionization mass spectrometry in negative mode using multiple reaction monitoring (MRM). The experimental results showed good linearities (r²>0.99) in their concentration ranges. The limits of detection (LODs) were 0.5 and 1 μg/L, and the limits of quantitation (LOQs) were 2 and 5 μg/L for PFOA and PFOS, respectively. The recoveries of PFOA and PFOS ranged from 86.4% to 116.9% at three spiked levels with the relative standard deviations (RSDs) between 4.3% and 14.4% (n=6). The proposed method was demonstrated as accurate, efficient, eco-friendly, and suitable for the determination of the migration of PFOA and PFOS from FCMs.

Quantitative Analysis of Four Catechins from Green Tea Extract in Human Plasma Using Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry for Pharmacokinetic Studies

Green tea is consumed as a beverage worldwide and has beneficial effects, such as a lower risk of cardiovascular disease and cancer. A quantitative analysis of the beneficial components in plasma is important for understanding the potential health benefits of green tea. Four catechins—epigallocatechin-3-gallate (EGCG), epicatechin-3-gallate (ECG), epigallocatechin (EGC), and epicatechin (EC)—which account for the majority of the components of green tea, were analyzed by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). In this study, a validated method was optimized to obtain the blood concentrations after the one-time ingestion of 630 mg green tea extract with digoxin and then after the ingestion of 630 mg green tea repeatedly for 15 days. The calibration curve, including the LLOQ, was constructed over 1–500 ng/mL for EGCG, ECG, and EGC and 0.1–50 ng/mL for EC. The method for inter- and intra-validation was applied, acceptable for both accuracy and precision. We successfully developed an appropriate UPLC-MS/MS method for human plasma with good reproducibility and sensitivity. Thus, this method could be applied for future preclinical and clinical studies on EGCG, ECG, EGC, and EC.

[Rapid determination of benzo[a]pyrene in foods by ultra performance liquid chromatography-triple quadrupole mass spectrometry with atmospheric pressure chemical ionization]

A method for the determination of benzo[a]pyrene in foods was developed by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) based on isotope dilution and molecularly imprinted solid-phase extraction (MIP-SPE). The target analyte in samples was extracted with n-hexane after spiked with benzo[a]pyrene-d₁₂, and purified using MIP-SPE to eliminate most of the coextracts. The separation of benzo[a]pyrene was carried out on an XBridge BEH C₁₈ column with gradient elution of methanol and water. An atmospheric pressure chemical ionization (APCI) interface was used as the ion source and the analysis was performed in the multiple reaction monitoring (MRM) mode. Benzo[a]pyrene levels in the range of 0.07-50 μg/kg were measured accurately by this method, and the limit of quantification (LOQ) was 0.07 μg/kg. The average recoveries were between 86% and 104% with the relative standard deviations within 2.3%-14%. The method was sensitive and accurate, and it has been successfully applied to the measurement of benzo[a]pyrene in food samples.

Seed metabolomic study reveals significant metabolite variations and correlations among different soybean cultivars

Soybean [Glycine max (L.) Merr.] is one of the world's major crops, and soybean seeds are a rich and important resource for proteins and oils. While "omics" studies, such as genomics, transcriptomics, and proteomics, have been widely applied in soybean molecular research, fewer metabolomic studies have been conducted for large-scale detection of low molecular weight metabolites, especially in soybean seeds. In this study, we investigated the seed metabolomes of 29 common soybean cultivars through combined gas chromatography-mass spectrometry and ultra-performance liquid chromatography-tandem mass spectrometry. One hundred sixty-nine named metabolites were identified and subsequently used to construct a metabolic network of mature soybean seed. Among the 169 detected metabolites, 104 were found to be significantly variable in their levels across tested cultivars. Metabolite markers that could be used to distinguish genetically related soybean cultivars were also identified, and metabolite-metabolite correlation analysis revealed some significant associations within the same or among different metabolite groups. Findings from this work may potentially provide the basis for further studies on both soybean seed metabolism and metabolic engineering to improve soybean seed quality and yield.