Development Of Online Pre-Enrichment Chromatography-mass Spectrometry And Their Application

According to different methods of sample preparation for chromatography-mass spectrometry,this paper reviewed solvent extraction,solid phase extraction,supercritical fluid extraction and derivatization preparation methods.Gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry analysis of high fatty acids were also studied.What's more,The application of online preconcentration magnetic solid phase extraction in the determination of benzene series was explored.1.A method for the determination of high fatty acids in tobaccos by liquid-liquid extraction-GC-MS-internal standard method was developed.The sample was subjected to methyl esterification and then injected directly into the sample for GC-MS analysis using heptadecanoic acid as internal standard for quantitative analysis.The selection of internal standard and different solvent,the concentration of methyl esterification and derivatization time were optimized.The results showed that the average spiked recoveries of analytes were 92%-97%,the relative standard deviations(RSDs)were 2.1%?2.6%(n=5),and the method detection limit(LOQs)were 0.002-0.014 mg/g.The method has high stability and suitable for determining high fatty acids in tobacco.2.A method for determining 7 high fatty acids in tobaccos by liquid chromatography-tandem mass spectrometry(LC-MS/MS)was developed.The sample was saponified with KOH-methanol solution,extracted with dichloromethane,purged with nitrogen and then injected directly into the sample for LC-MS/MS analysis using heptadecanoic acid as an internal standard for quantitative analysis.Aiming at the properties and sample impurities of the analytes,the parameters such as chromatography and mass spectrometry conditions,pretreatment processes were optimized.The final target was verified by infrared spectroscopy(FT-IR),mass spectrometry(MS)and nuclear magnetic resonance(NMR).The high fatty acids were analyzed under the Psoudo-molecular multiple reaction monitoring transition mode with negative electrospray ionization source(ESIP).Results showed that the linear regression lines for peak area ratios(analyte/internal standard)plotted against the concentration ratios(analyte/internal standard)fitted well(R2>0.9818)for high fatty acids,The recoveries of standard addition ranged from 87.5%to 109%with relative standard deviation(RSDs)of 1.1%-4.7%.The limits of detection was between 0.0004 and 0.007 mg/g,and that of quantifications was between 0.001 and 0.02 mg/g.This method is simple,accurate and suitable for the determination of 7 high fatty acids in tobacco.3.The magnetic carbonyl iron powder(CIP)was condensed with the gel solution by using tetraethyl orthosilicate(TEOS)as the silicon source,hydrochloric acid as the hydrolysis catalyst and diethylamine ethanol solution as the condensation reaction catalyst to synthetize the magnetic particles(CIP@SiO2@PDMS).The concentration of hydrochloric acid and diethylamine ethanol solution,the water content and the volume ratio of TEOS and hydroxyl terminated polydimethylsiloxane(PDMS-OH)were optimized.The structure of the CIP@SiO2@PDMS magnetic particles were characterized with scanning electron microscopy(SEM),transmission electron microscopy(TEM),infrared spectroscopy and thermogravimetric analysis(TGA).Then the magnetic particles were used as adsorbent for on-line magnetic solid phase extraction(MSPE)to determine benzene,toluene,ethylbenzene and xylenes(BTEX)in water samples by gas chromatography-mass spectrometry.Suspension stability,adsorption and desorption conditions were optimized.Results showed that the method can be applied to the enrichment and determination of BTEX in water samples.Under the experimental conditions,The limits of detection(LODs)and limits of quantitation(LOQs)for BTEX were observed to be 0.02?0.05 ng/L and 0.067-0.167 ng/L,respectively,the relative standard deviations(RSDs)were less than 4.5%,recoveries were obtained in the range of 95%-106%.