Studies On The Influence Of Some Factors And Application For Pyrolytic Methylation Gas/Chromatography Technique

The analysis of polar compounds in aqueous solution such as organicacid, alcohol and hydroxybenzene requires extensive sample-pretrementincluding derivatization, extraction, evaporation etc., and then has beendetermined by gas chromatography. Otherwise, using the pyrolyticmethylation/gas chromatography technique, the processes above can becompleted by only one step successfully. On the one hand, although thistechnique applied for carboxyl compounds is well reported due to itsremarkable effect of derivatization, the quantificational research onhydroxyl compounds is limited. So some influence factors andapplication on hydroxyl compounds in aqueous solutions by the pyrolyticmethylation/gas chromatography technique have been studied. On theother hand, polyunsaturated fatty acids can be partially isomerized ordegraded using the technique in the presence of TMAH due to its strongalkalinity. Therefore, the application of the technique in the presence ofTMAAc also has been discussed.In the first chapter, the history, chemical process, and the advantage and shortage of the pyrolytic methylation/GC were briefly described. Then, applications of this method to analysis of lipids, waxes, natural resins, wood products, carbohydrates, proteins etc. were discussed.In chapter 2, in order to obtained the highest yield of methyl derivatives of benzoic acid, phenol, butane-1,4-diol and chrysin by pyrolytic methylation-GC, four important factors such as reaction temperature, the amount and the kind of derivative reagent and the way of injection were determined. The obtained results showed that excessive 25% TMAH aqueous solution at 400℃enabled the 1μ1 mixture of benzoic acid, phenol, butane-1,4-diol and chrysin at 500 mg/l, respectively, were converted into their corresponding methyl compounds. The yield of methyl derivatives of studied compounds were corresponding to their chemical structures and acidity. The methyl derivatives of butane-1,4-diol were not observed on the chromatogram obtained using TMAAc as regent, mainly due to TMAAc being a weak base.In chapter 3, a method to determine dihydroxyacetone (DHA) and glycerol in fermentation broth was developed on the basis of pyrolytic methylation/gas chromatography (GC) using a vertical microfurnace pyrolyzer. Traditional analytic techniques such as enzymic, spectrophotometric methods and thin-layer chromatography for DHA and glycerol analysis, usually required extensive sample-pretrement, which might reduce the analytical precision, because fermentation samples were aqueous solutions commonly and the sample matrix was also very complicated. In addition, DHA and glycerol could not be determined by these traditional analytic techniques simultaneously. With the on-line pyrolytic methylation in the presence of an organic alkali, tetramethylammonium hydroxide (CH₃)₄NOH, TMAH), DHA and glycerol were converted into their corresponding methyl ethers. Thus, obtained results showed that the achieved calibration curves exhibit good linearity with regression coefficients of 0.996 and 0.998 for DHA and glycerol at the concentration range from 1 to 100 g/l, respectively. The limit of detection reached 0.012 and 0.016 g/l for DHA and glycerol, and the precision was quite high with the R.S.D. within 5.1%. The recoveries of DHA and glycerol were 94 to 96 %, respectively. The results proved that this on-line pyrolytic methylation/GC technique was a rapid, convenient and highly sensitive method for monitoring the bioprocesses of DHA.In chapter 4, a method to determine the preservatives of benzoic acid and sorbic acid in soft drinks was developed on the basis of pyrolytic methylation/gas chromatography (GC) without using any pretreatment procedures. With the on-line pyrolytic methylation in the presence of an organic alkali, tetramethylammonium acetate (CH₃)₄NOOCCH₃, TMAAc), the isomerized and degraded of sorbic acids could be minimized. Under optimum conditions, the linear range achieved were 5 and 10～2500 mg/l for benzoic and sorbic acid, respectively. The detection limit of benzoic acid and sorbic acid could reach 0.13 and 0.85 mg/l, respectively. The R. S. D. of the determination was 5.6% for the two preservatives in real soft drink samples. The recoveries of benzoic and sorbic acid were ranged from 91.9 to 110.0%, respectively. The results proved that the on-line technique could determined benzoic acid and sorbic acid in soft drinks simultaneously.In the last chapter, the main results obtained from this research were summarized. Then, the problems to be considered for this research and the possible future trends in this field were also discussed.