Enantiomeric Analysis Of Alkaloids In Tobacco And Cigarette Smoke By Multi-Dimensional Gas Chromatography And Mass Spectrometry

Tobacco and cigarette smoke are among the most complex mixtures.More than 3800 and 4800 substances have been identified in tobacco and tobacco smoke, respectively.Although capillary gas chromatography has great separating capability,it is still very reluctant to analytical tasks of tobacco and tobacco smoke. Multi-dimensional gas chromatography(MDGC) can fully make use of selectivity differences of pre- and analytical columns.Those overlapped constituents on a non-polar pre-column normally get a satisfactory resolution on a polar analytical column.In addition to this,the peak capacity of MDGC(GC×GC) is also substantially increased than conventional one dimensional GC.Base on the double contributions of selectivity and peak capacity,the separating power of MDGC is drastically enhanced than the one dimensional GC.Since later in 1980s,the great separation capability of MDGC has been shown in the analysis of tobacco and tobacco smoke by foreign tobacco industries.However,the research and applications of MDGC techniques are rarely seen in domestic tobacco industry.MDGC has been widely used in enantiomeric analysis and has many advantages than single chiral GC column.However,there have been no related publications in tobacco industry.In this paper,concepts,theories,instrumentation and technique progress of MDGC and comprehensive two dimensional GC(cMDGC) have been extensively reviewed, features of the related techniques has been compared.The chiral GC stationary and tactics for chiral GC separation have also been reviewed.With a comprehensive understanding of MDGC techniques,innovative results have been obtained on aspects of instrumentations and analytical methodologies.Chirality of alkaloids in tobacco and tobacco smoke have been studied by MDGC/MS,some new findings involved in tobacco chemistry have been established.The major studies and results were shown as follows:1.A fully automatic and all EPC controlled capillary-capillary MDGC system were established.Based on SGE MDS 6890,the heart-cutting valve was replaced by a press-fit glass Y-splitter with zero dead volume.A GC controlled EPC module was used to provide three paths of gas for the middle pressure,cutting pressure and actuation of cold trap,respectively.The new system has following advantages:better inertness,less dead volume,more stable and lower cost.The great separating capability of the new system was manifested in the complete analysis of essential oil of a flue-cured tobacco.2.A fully automatic megabore-capillary MDGC with online enrichment was developed.Based on SGE MDS2000,the external controller was replaced by a GC valve box.The external needle valve for mid-split adjustment was replaced by a fused silica restrictor in GC oven.The solenoid valve for mid-split was replaced by a gas actuated on/off valve;actuating gas was shared with heart-cutting valve.The advantages of the new system include enhanced intergradations and automation.The pneumatic design is more reasonable.Selection of restrictors is easier.The cost is low.3.Innovations on MDGC methodology.By using a pressure/flow software for capillary columns,setting up procedure for constant flows for the 1^st and 2^nd columns were put forward.The procedure of calculation of restrictor was also provided.The method development of MDGC became much easier with the help of software.4.Chiral GC separation of nicotine enantiomers was optimized,for the first time, formation mechanism of R-(+)-nicotine in tobacco smoke was confirmed by experimental evidences.By using on-lined pyrolyzer-chiral MDGC/NPD,it was found that,racemization of S-(-)-nicotine reagent was highly synchronous to its thermal degradation process.By using on-lined pyrolyzer-chiral MDGC/NPD and pyrolyzer-GC/MS,it was found that,racemization of S-(-)-nicotine in tobacco was also highly synchronous to its thermal degradation process.During smoking process, thermal racemization of S-(-)-nicotine in tobacco is the main source of R-(+)-nicotine in smoke.5.A method for determination of 14 alkaloids in tobacco has been established. Different types of tobacco materials and cigarette fillers have been analyzed and the results were given.6.A method for chiral analysis of anatabine,nornicotine and anabasine in tobacco has been established.By simple solvent extraction and trifluoroacetic anhydride derivatisation,tobacco alkaloids were analyzed by chiral MDGC.The sample pretreatment is convenient and the repeatability is excellent with RSD below 1.5%.Through composite analysis of commercial tobacco,regular patterns of the enantiomeric composition in flue-cured,burley and oriental tobacco were elucidated.