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    Chinese Journal of Chromatography
    2019, Vol. 37, No. 11
    Online: 08 November 2019

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    Content
    Volume 37, Number 11 Content
    2019, 37 (11):  0-0. 
    Abstract ( 14 )   PDF (5047KB) ( 17 )  
    Reviews
    Progress in the application of functional materials in proteomics research
    XIANG Xiaochao, JIAO Fenglong, ZHANG Yangjun, QIAN Xiaohong, QIN Weijie
    2019, 37 (11):  1135-1141.  DOI: 10.3724/SP.J.1123.2019.04041
    Abstract ( 123 )   [Full Text(HTML)] () PDF (880KB) ( 184 )  
    With the increasing depth of proteomic identification, quantitative accuracy and increasing analytical speed, new challenges are being encountered in the development of proteomics methods. Traditional proteomics methods are time-consuming and have low sensitivity and poor accuracy; hence, they do not satisfy the new demands in proteomics research. Preparation of novel materials with specific functions via chemical and biochemical routes or by methods based on electricity, magnetism, heat, and photoirradiation is the key to overcome the limitations of traditional analytical techniques and promote active research in the field of proteomics. This paper reviews the recent advances in the application of functional materials in proteomics researches.
    Articles
    Simultaneous rapid determination of 84 toxic plant constituents in plasma and urine by ultra-performance liquid chromatography- triple quadrupole/linear ion trap mass spectrometry
    ZHANG Xiuyao, CAI Xinxin, ZHANG Xiaoyi, LI Ruifen
    2019, 37 (11):  1142-1156.  DOI: 10.3724/SP.J.1123.2019.04049
    Abstract ( 92 )   [Full Text(HTML)] () PDF (4084KB) ( 70 )  
    Supporting Information
    An ultra-performance liquid chromatography-triple quadrupole/linear ion trap mass spectrometry (UPLC-Qtrap MS) method was developed for the determination of 84 toxic plant constiuents in plasma and urine. Plasma was precipitated by acetonitrile to remove proteins and then passed through a Prime HLB SPE column to remove phospholipids, while urine was diluted with methanol. Chromatographic separation of the analytes was achieved on an Acquity BEH C18 column (100 mm×2.1 mm, 1.7 μm) by gradient elution using the mobile phase of 0.1% (v/v) formic acid and 2 mmol/L ammonium formate both in 97% (v/v) acetonitrile aqueous solution and water. Electrospray ionization mass spectrometry was carried out in the positive ion mode with multiple reaction monitoring-information dependent acquisition-enhanced product ion scan mode (MRM-IDA-EPI). The 84 analytes were quantified by the matrix working standard curve internal standard method, and a good linear relationship was observed, with correlation coefficients of ≥ 0.9911. The limits of detection (LODs) in plasma and urine were 0.01-1 μg/L and 0.03-2 μg/L, respectively. The intra- and inter-day precisions of these analytes were 0.7%-18.4% and 1.1%-18.5%, and the accuracy of all analytes ranged from 70.6% to 124.5%. This method is simple, sensitive, and accurate for the measurement of these analytes in plasma and urine for both clinical and forensic applications.
    Determination of nine B vitamins in peptone using ultra high performance liquid chromatography-tandem mass spectrometry
    JIANG Sha, XIN Hui, MO Rigen, DU Yan, LI Zhenlian, ZHU Yeqing
    2019, 37 (11):  1157-1161.  DOI: 10.3724/SP.J.1123.2019.04017
    Abstract ( 103 )   [Full Text(HTML)] () PDF (847KB) ( 80 )  
    A method using ultra high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for the determination of nine B vitamins in peptone. The samples were extracted with water. The analytes were separated on a Syncronis C18 column (100 mm×2.1 mm, 1.7 μm). The nine B vitamins were detected by ESI-MS/MS under the multiple reaction monitoring (MRM) mode, and the analysis was completed in 8 min. Quantification analysis was performed by using the external standard method. The correlation coefficients (R2) of the nine B vitamins in their linear ranges were greater than 0.999. The limits of detection were 0.09-1.67 μg/L. The relative standard deviations of the method were less than 3% (n=6). The mean recoveries of the nine B vitamins were 80.2%-103.9% at different spiked levels. The method is simple, accurate and sensitive, and is suitable for the determination of the nine B vitamins in peptone.
    Analysis of monosaccharide composition in polysaccharides from Lycium barbarum L. by precolumn labeling under mild conditions and high-performance liquid chromatography coupled with mass spectrometry
    ZHAO Mengxin, WANG Zelan, MENG Zhe, LI Jiguang, LI Heping, LIU Wanyi
    2019, 37 (11):  1162-1172.  DOI: 10.3724/SP.J.1123.2019.04013
    Abstract ( 219 )   [Full Text(HTML)] () PDF (1946KB) ( 338 )  
    A method for the separation, identification, and determination of fructose and various aldehyde monosaccharides was established by precolumn labeling with 1-phenyl-3-methyl-5-pyrazolone (PMP) and high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS). The separation was performed on a Kromasil-C18 column (100 mm×4.6 mm, 3.5 μm) with gradient elution. The detection was performed by electrospray ionization mass spectrometry in selected ion monitoring (SIM) mode. In this study, the derivatization mechanism of PMP-labeled fructose was proposed under mild NH3·H2O conditions. The suggested method showed good linearity in the corresponding mass concentration ranges, with the correlation coefficients (r2) > 0.9947. The limits of detection (LODs) and limits of quantification (LOQs) were in the ranges 0.003 to 0.05 mg/L and 0.01 to 0.15 mg/L, respectively. The recoveries in spiked Lycium barbarum L. samples were 65.1% to 116.2%, with relative standard deviations (RSDs) of less than 10.2%. By virtue of its simplicity, high sensitivity, and good repeatability, the method could be successfully applied to the analysis of the monosaccharide composition in polysaccharides of Lycium barbarum L. from four planting areas. Results showed that the isolated polysaccharides comprise mannose, fructose, rhamnose, galactose, glucose, xylose, arabinose, and ribose. The concentration distribution of various monosaccharides differed notably depending on the planted environmention. The proposed method is expected to be of great significance in standardizing the quality control of polysaccharides.
    Rapid screening of sibutramine and five derivatives in health food by high performance liquid chromatography-quadrupole/electrostatic orbitrap high-resolution mass spectrometry
    HONG Deng, XIE Wen, HOU Jianbo, HU Xiaoli, SHI Yingzhu, LI Jie
    2019, 37 (11):  1173-1178.  DOI: 10.3724/SP.J.1123.2019.05017
    Abstract ( 79 )   [Full Text(HTML)] () PDF (935KB) ( 106 )  
    A rapid screening method was developed to determine sibutramine and five derivatives in health food by high performance liquid chromatography-quadrupole/electrostatic orbitrap high-resolution mass spectrometry (HPLC-Q/Orbitrap HRMS). The sample was extracted with methanol via ultrasonic-assisted extraction coupled with high-speed centrifugation. Separation was performed on a Hypersil Gold column (100 mm×2.1 mm, 3 μm) by gradient elution with methanol/water (containing 0.15%(v/v) formic acid) as the mobile phase. The positive full mass scan/date-dependent MS2 (Full MS/dd-MS2) mode was used during MS detection, and quantification was achieved by resolution of the precursor mass. The analytes in the sample were separated, and accurate mass and MS2 fragment ions were simultaneously attained within 8 min. The results indicated that the obtained mass accuracy errors of the six analytes were less than 1×10-6. Good linearities were obtained in the range of 0.5-20.0 μg/L, and all correlation coefficients were higher than 0.999. The limits of quantification were 25 μg/kg and the recoveries were in the range of 93.5%-103.5% with relative standard deviations of 1.5%-7.7%. This simple-pretreatment, rapid, accurate, high-sensitivity, and high-selectivity method can be used in the rapid screening and quantitative analysis of sibutramine and its derivatives in health food.
    Rapid determination of glyphosate, aminomethyl phosphonic acid, glufosinate, and ethephon residues in environmental water by direct injection-ultra performance liquid chromatography-triple quadrupole mass spectrometry
    HE Shuhai, CAO Xiaocong, WU Haijun, LI Tengya, ZHANG Mingshan, LIANG Yan, CHEN Biaojuan
    2019, 37 (11):  1179-1184.  DOI: 10.3724/SP.J.1123.2019.05011
    Abstract ( 203 )   [Full Text(HTML)] () PDF (2273KB) ( 181 )  
    A simple method based on direct injection-ultra performance liquid chromatography-triple quadrupole tandem mass spectrometry (UPLC-MS/MS) was established for the rapid determination of glyphosate, aminomethyl phosphonic acid, glufosinate, and ethephon residues in environmental water. The water samples were filtered through a 0.22-μm filter membrane or frozen and centrifuged to remove impurities, and then, the filtrate was directly subjected to quantitative analysis without derivatization. The analytes were separated on a Metrosep A Supp 5 column (150 mm×4.0 mm, 5 μm), and gradient elution was carried out using an ammonium bicarbonate-ammonia solution as the mobile phase. The data were collected by positive electrospray ionization in the multiple reaction monitoring (MRM) mode. The results showed that the correlation coefficients (r) of the linear calibration curves were greater than 0.999 in the corresponding linear ranges (0.50-50.0 μg/L). The detection limits of the analytes were 0.05-0.09 μg/L. The recoveries of glyphosate, aminomethyl phosphonic acid, glufosinate, and ethephon were in the ranges 76.3%-108%, 83.0%-107%, and 87.0%-105% at low, medium, and high spiked levels, respectively. The corresponding relative standard deviations were in the ranges 2.0%-12.3%, 2.4%-5.6%, and 2.7%-6.8%. Using this method, 34 water samples collected from Hainan Province were analyzed, among which 30 drinking water sources were found to be free from the four pesticides. Glyphosate and aminomethyl phosphonic acid were detected in three water samples near a betel nut orchard, while glufosinate and aminomethyl phosphonic acid were detected in a water sample near a banana orchard. This method is advantageous over the traditional derivatization method because of its simple operation, good reproducibility, and high accuracy; furthermore, the matrix interference effect is absent. Thus, this method is suitable for analyzing glyphosate, aminomethyl phosphonic acid, glufosinate, and ethephon residues in environmental water samples.
    Determination of nine bisphenols in children's water bottle by online enrichment coupled with high performance liquid chromatography-fluorescence detection
    HAN Shuying, SONG Yilin, KANG An, DENG Haishan, ZHU Dong, CHI Yumei
    2019, 37 (11):  1185-1192.  DOI: 10.3724/SP.J.1123.2019.04016
    Abstract ( 138 )   [Full Text(HTML)] () PDF (1300KB) ( 128 )  
    A method was developed for the rapid determination of bisphenol A (BPA) and eight structural analogs in children's plastic water bottles by online enrichment coupled with high performance liquid chromatography-fluorescence detection (HPLC-FLD). The correlation coefficients of the nine bisphenols were greater than 0.998. The limits of detection (LOQs) ranged from 0.13 ng/L to 66.7 ng/L. The recoveries ranged from 90.7% to 112.4% (RSD<11.3%, n=6). This method was applied to monitor nine bisphenols in children's water bottles. The results showed that except 4,4'-(9H-fluoren-9-ylidene)bisphenol (BPFL), all the remaining eight bisphenols were detected in different water bottles. The amounts of bisphenols leached increased with the increase of soaking time, and decreased after washing several times at 100℃. The proposed strategy is rapid, sensitive, reliable and eco-friendly, and is suitable for the simultaneous analysis of new bisphenols in water samples.
    Isolation and preparation of polyphenols from grape seed by high-speed counter-current chromatography combined with preparative high performance liquid chromatography
    WANG Wei, HE Tianyu, LAN Tao, XI Xingjun, ZHAO Xinying
    2019, 37 (11):  1193-1199.  DOI: 10.3724/SP.J.1123.2019.05024
    Abstract ( 108 )   [Full Text(HTML)] () PDF (899KB) ( 110 )  
    Eight polyphenols were separated from grape seed by high-speed counter-current chromatography (HSCCC). The separation was performed using a two-phase solvent system composed of 1-butanol-ethyl-water (1:14:15, v/v/v) and n-hexane-ethyl-water (1:10:10, v/v/v). The upper and lower phases were used as the stationary and mobile phases, respectively. A flow rate of 2.0 mL/min was employed for the separation. The apparatus was rotated at 900 r/min, and the detection wavelength was set at 280 nm. Under the selected conditions, procyanidins B1, procyanidins B2, gallic acid, epicatechin gallate, and catechin were obtained from the grape seed extracts with a purity of 98.5%, 97.2%, 98.3%, 98.9%, and 96.7%, respectively. Epicatechin, epicatechin gallate, and gallocatechin gallate were obtained by preparative high performance liquid chromatography with the purity of 99.2%, 99.3%, and 99.2%, respectively. The proposed method is simple and shows high separation efficiency, and will be of great importance for the comprehensive utilization of grape seed.
    Quality consistency evaluation of Fufanggancao tablets based on the control mode of standard preparation and quantitative fingerprint
    YAN Hui, SUN Guoxiang, CHI Hanxiao, ZHANG Jing, SUN Wanyang, HOU Zhifei, LI Xianlin, PU Daojun, CHEN Zhenhong
    2019, 37 (11):  1200-1208.  DOI: 10.3724/SP.J.1123.2019.06010
    Abstract ( 107 )   [Full Text(HTML)] () PDF (960KB) ( 106 )  
    The control mode of standard preparation (SP) and quantitative high performance liquid chromatography (HPLC) fingerprint of Fufanggancao tablets (FFGCTs) combined with the quantification of five markers were successfully developed and applied to the precise and accurate assessment of the quality consistency of 145 FFGCTs from nine manufacturers. The profiling was determined by reversed-phase HPLC at 220 nm wavelength, where the reference fingerprint (RFP) of the FFGCTs reserved as standard preparation was established. Subsequently, the SP-RFP was considered as the evaluation standard, and a systematic quantitative fingerprint method was applied to the integrative quality discrimination of 145 batches of FFGCTs, from both qualitative and quantitative perspectives. Besides, the chromatographic systematic error of quantitative fingerprints was corrected by the double marker calibration method. The results showed that the qualities of the FFGCTs from the nine manufacturers were completely qualified. Moreover, all raw herb fingerprints and the simulated sample were determined by using the combined chromatographic conditions applied to the FFGCTs, which helped identify the source of the profiling peaks in the preparation and establish the correlation between the raw herb fingerprints and the preparation fingerprints. This eventually aided the intelligent prediction of the quality of the preparation or raw herbs and effective prevention of the inputs of inferior raw materials. In addition, we employed the ultraviolet full fingerprint dissolution method to differentiate the FFGCTs from five manufacturer dissolution, in which the rationality of the preparation process was evaluated. The method is feasible and accurate, and it can be applied to evaluate the quality and process technology consistency of FFGCTs. This paper provides a fundamental standard preparation evaluation mode and the basic operation procedure for the quality consistency assessment of traditional Chinese medicine.
    Primary study on computer-aided qualitative and quantitative radial thin-layer chromatography methods for analysis of Yiqing tablets
    TIAN Chunjie, CHEN Mingxin, WANG Danqi, WANG Hongling, GUAN Jianhuan, ZHANG Mengting, SUN Guoxiang
    2019, 37 (11):  1209-1214.  DOI: 10.3724/SP.J.1123.2019.04020
    Abstract ( 76 )   [Full Text(HTML)] () PDF (1326KB) ( 80 )  
    Radial thin-layer chromatography (RTLC) is a form of chromatography in which the sample and developing agent/solvent are applied at the edge of a circle on the silica-layered TLC plate. The sample components are radially transported from the center of the circle toward the periphery by the solvent flow. RTLC is an efficient separation and semi-preparation method, with the advantages of fast separation, low diffusion, and absence of tailing at a certain distance. Although RTLC isolation has been well documented in the literature, there are only a few qualitative and quantitative reports on this technique. In this study, a self-programming module combined with image processing software was adopted for digital processing of RTLC images, and a digital atlas was created. Qualitative and quantitative verification of RTLC was then conducted. With the aid of computer technology, qualitative and quantitative methods of radially expanded TLC for Yiqing tablets were investigated. The results showed that the qualitative RTLC method has good reliability, but the quantitative RTLC method has inherent drawbacks, which may be associated with the experimental environment. We strongly believe that better separation and data acquisition equipment, as well as the combination of computer image processing and programming methods, will open up infinite possibilities of analysis/separation using RTLC-based techniques. We also believe that TLC will take a new step in the future with the assistance of computer technology.
    Simultaneous determination of nine flavor compounds in pasteurized milk by gas chromatography- triple quadrupole mass spectrometry
    LIU Tong, WANG Yujiao, WANG Xiujuan, CUI Dongwei, ZHANG Feng
    2019, 37 (11):  1215-1220.  DOI: 10.3724/SP.J.1123.2019.04033
    Abstract ( 82 )   [Full Text(HTML)] () PDF (1257KB) ( 95 )  
    A gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) method was established for the simultaneous determination of nine flavor compounds (hydrocoumarin, vanillin, coumarin, ethyl vanillin, methyl vanillin, 7-methylcoumarin, 7-methyoxycoumarin, 7-ethoxy-4-mrthyl coumarin, pyranocoumarin) in pasteurized milk. The samples were extracted with ethanol and subjected to whirlpool oscillation. After centrifugation, the supernatant was filtered through a membrane, and the components were separated on a DB-5MS column. The nine analytes were detected by GC-MS/MS in the multiple reaction monitoring (MRM) mode and quantified by a matrix-matched external standard method. Good linearities in the range of 1-200 μg/L were observed for the nine flavor compounds. The linear correlation coefficients (R2) were greater than 0.997. The limits of detection and limits of quantification were 0.002-0.1 μg/kg and 0.001-2 μg/kg, respectively. The average recoveries were 90.3%-110.6%. Both the intra-day and inter-day RSDs were less than 10%. The developed method is simple, rapid, accurate and sensitive, and can be used for the simultaneous determination of the nine flavor compounds in pasteurized milk.
    Determination of 29 adjuvants in pesticide formulations by gas chromatography-mass spectrometry
    TANG Xiangkai, FENG Dejian, SHI Xiefei, LI Huaiping
    2019, 37 (11):  1221-1227.  DOI: 10.3724/SP.J.1123.2019.03038
    Abstract ( 88 )   [Full Text(HTML)] () PDF (1118KB) ( 100 )  
    A method based on gas chromatography-mass spectrometry (GC-MS) was developed for the simultaneous determination of 29 adjuvants in pesticide formulations. The pesticide formulation was diluted with methanol, and the supernatant was filtered through a 0.22-μm membrane. After separation on a VF-1701MS column, the analytes were detected by mass spectrometry in the selected ion monitoring (SIM) mode and quantified using the external standard method. Good linearities were obtained for the 29 pesticide adjuvants in the linear range of 6.2-400.0 mg/L, with correlation coefficients (R2) larger than 0.99. The limits of quantification (LOQs) were 4.4-439.1 mg/kg. The average recoveries in emulsifiable concentrate (EC) and soluble concentrate (SL) samples ranged from 82.0% to 111.9% and from 82.6% to 112.9%, respectively. The relative standard deviations (RSDs, n=6) ranged from 0.4% to 7.2% and from 0.3% to 8.2%, respectively. Finally, 110 pesticide formulation samples were detected; 11 kinds of pesticide adjuvants, including phenol, N-methyl pyrrolidone, dichloromethane, and n-hexane, were detected in 28 samples with contents ranging from 0.05% to 15.65%. The proposed method is simple, sensitive, and accurate, and is suitable for the simultaneous determination of the 29 adjuvants in pesticide formulations.
    Determination of 67 volatile organic compounds in ambient air using thermal desorption-gas chromatography-mass spectrometry
    ZHU Xiaoping, MA Huilian, ZHU Xiuhua, CHEN Jiping
    2019, 37 (11):  1228-1234.  DOI: 10.3724/SP.J.1123.2019.04043
    Abstract ( 126 )   [Full Text(HTML)] () PDF (1341KB) ( 103 )  
    A method based on thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) was developed for the simultaneous analysis of 67 volatile organic compounds (VOCs) in ambient air. In this study, the adsorption effects of five kinds of stainless steel sorbent tubes for 78 VOCs were compared. The results revealed that a multisorbent bed with Carbograph 1TD and Tenax TA shows good adsorption effect for the 67 target compounds. The breakthrough rates of all the target compounds were less than 10% when high-purity helium gas was continuously purged for 45 min at 30 mL/min. The analytes included aromatic hydrocarbons, aliphatic hydrocarbons, halogenated hydrocarbons, and oxygen-containing volatile organic compounds. The thermal desorption conditions for the determination of the target substances were optimized. In the range 5-100 ng, the chromatographic response of the target compounds had a good linear relationship with their corresponding amounts, and the correlation coefficient (r) was between 1.0000 and 0.9977. The method detection limits (MDLs) were 0.3-2.4 ng or 0.3-2.4 μg/m3, as calculated by a 1 L sampling volume. The method was validated by means of recovery experiments (n=7) with the addition of 20 ng standard samples. The recoveries of all the target compounds were in the range of 81.6%-114.9%, and their relative standard deviations (RSDs) were in the range of 1.2%-10.2%. The VOCs present in the air in a carriage were detected using this method. The 19 target compounds included esters, halogenated alkanes, halogenated olefins, and aromatic substances, whose concentrations ranged from 1.1 to 84.1 μg/m3. These results indicated that our method is accurate, reliable, and sensitive, and can allow for accurate quantification of the 67 target pollutants in ambient air.
    Quality evaluation of Chenxianghuaqi tablets by gas chromatographic fingerprint of volatile components
    QING Wangwang, SHI Yutao, YANG Lin, ZHANG Ruiteng, ZHANG Jingqing, HE Dan
    2019, 37 (11):  1235-1240.  DOI: 10.3724/SP.J.1123.2019.04007
    Abstract ( 63 )   [Full Text(HTML)] () PDF (1344KB) ( 70 )  
    A gas chromatographic fingerprint combined with chemical pattern recognition was successfully developed and applied to assess the quality consistency of 20 Chenxianghuaqi tablets. Volatile components from the 20 Chenxianghuaqi tablets were extracted with ethanol under ultrasonic conditions. n-Octadecane was used as the internal standard to calculate the amounts of the three main components and to confirm the relative peak areas of the other components. Gas chromatographic fingerprints of the 20 Chenxianghuaqi tablets were established. There were 11 common peaks in the fingerprints, and the similarity of each batch of samples was obtained. Ten common peaks were identified by gas chromatography-mass spectrometry, with reference comparison. The obtained fingerprints were used for the chemical pattern recognition, including hierarchical cluster analysis and the principal component analysis. Different batches of Chenxianghuaqi tablets could be differentiated effectively, and major markers that led to differences among the sample batches were identified. The method proposed in this study is comprehensive and reliable, and it can be used as a valuable reference to evaluate and control the quality of Chenxianghuaqi tablets.
    Technical Notes
    Rapid screening and confirmation of 20 mycotoxins in grain products by ultrahigh performance liquid chromatography- quadrupole/electrostatic field orbitrap high- resolution mass spectrometry
    HU Qiaoru, CAO Peng, CONG Zhongxiao, LIANG Junni, SHA Meilan, LI Xiaoyu, YIN Dalu, LU Min
    2019, 37 (11):  1241-1248.  DOI: 10.3724/SP.J.1123.2019.03041
    Abstract ( 68 )   [Full Text(HTML)] () PDF (938KB) ( 76 )  
    A rapid method based on ultrahigh-performance liquid chromatography-quadrupole/electrostatic field orbitrap high-resolution mass spectrometry (UPLC-HRMS) was developed for the screening and confirmation of 20 mycotoxins in grain products. The samples were extracted with acetonitrile containing 2% (v/v) formic acid, and the extracts were cleaned up on Captive EMR-Lipid columns. The analytes were separated on a Thermo Hypersil Gold C18 column (100 mm×2.1 mm, 1.9 μm), and analyzed by UPLC-HRMS. The retention time and accurate mass of the parent ion were used for fast screening in full scan mode, while the accurate masses of the fragment ions were used for confirmation in the two-stage threshold-triggered full mass scan mode. The results revealed that the 20 mycotoxins showed good linear relationships in their respective mass concentration ranges. The correlation coefficients were not less than 0.99, and the limits of quantitation (LOQs) ranged from 0.25 to 20 μg/kg. The recoveries of the 20 mycotoxins in the sample ranged from 72.9% to 117.8% with the relative standard deviations (RSDs) from 2.9% to 15.2% at three spiked levels (n=6). This method has the advantages of high sensitivity and reliability, and is thus suitable for the rapid screening and confirmation of 20 mycotoxins in grain products.