Separation Principle And Application Study Of Gas Chromatography With Coupled Capillary Column

Gas chromatography-mass spectrometry (GC-MS) is one of the major techniques for the determination of trace amount of food contaminants in complex matrix. GC-MS needs the columns with low bleed and high inertness. The preferred and supported columns at present are those with weak polarity, such as0-50%of phenylmethylpolysiloxane columns. However, it’s unsuitable to directly separate polar compounds because of the strong peak tailing effects. The determination methods and contaminations of the polar and low molecular compounds concerned in food safety were discussed in the introduction. Some of the techniques for improving peak tailing of polar compounds were summarized according to the present reports, such as the development of new columns with low bleed and strong polarity, the study of analyte protectants to compete with the adsorption of the active sites in the instrument system, the application of diversified derivatization methods. Coupled column was introduced according to the advantage and disadvantage discussions of the present methods. The purpose for this study was to develop columns with low bleed and applicable to GC-MS. The columns can be used to directly separate polar and low molecular compounds without derivatization and to simultaneously analyze the compounds with different types and polarities. The coupled columns introduced in this study include two parts:a1-3m of short column with middle or strong polarity and followed by a20-30m of analysis column with weak polarity and low bleed. Both parts are combined by a capillary column connector. The separation principle for polar compounds was studied according to the separation efficiency (such as the peak symmetry, width and retention time) of three groups of model compounds separated by six coupled columns with different polarities. The. studied model compounds include aliphatic and aromatic hydrocarbons, chloro-hydrocarbon and phenols, organic amine and amide, alcohols and phenols with weak and strong polarities, low and high boiling points, weak and strong hydrogen bond activities. The feasibility was also studied for the number of theoretical plate used to optimize the combination of the coupled column.The separation of the coupled column includes three parts as follows:1) The high separation efficiency of the polar short column to the polar compounds. By the strong polar molecular interactions, the diffusion effects and peak tailing were suppressed. A symmetrical peak would be helpful to obtain the high sensitivity and accurate quantification.2) The strong retention of the polar short column to the polar and low molecular compounds. Although only1-3m of polar columns were used, enough retention time was found for the polar and low molecular compounds to be separated from interference in complex matrix. Meanwhile, it’s only1-3m of polar columns would let the compounds with higher boiling points and stronger polarity to be eluted at lower oven temperature and less retention time.3) The normal separation ensured by the followed major analysis column with weak polarity and low bleed. Although the polar short column can improve the peak tailing and separation efficiency for the polar compounds, the column selectivity is not enough if only using1-3m of the polar columns. A20-30m of major analysis column followed to the short polar column is necessary to obtain the high selectivity of the whole coupled column.In the third and fourth parts of this study, the feasibility for the coupled column applied in complex matrix was discussed. It’s focused on the directly separation of the polar and low molecular compounds without derivatization in complex matrix in the third section. The compounds included the melamine in food, chloropropanols in flavoring and related foods, ester bonded chloropropanols in edible oils and acrylamide in fried and high temperature roasted foods. In the fourth section, the methods for simultaneous determination of the compounds with different types and polarities were studied. The methods include the determination of acutely poisonous rodenticides tetramine and fluoroacetamide in bio-material, melamine and urotropine in dairy and flavoring products, volatile and semi-volatile phenols in the soaking solution of water related products.Coupled column would be an ideal separation column for GC-MS because of its low bleed and compatibility of diversified polarity. It can be directly separated and measured by GC-MS for the compounds with higher molecular weight and enough characteristic ions for identity, such as melamine. Gas chromatography-tandem mass spectrometry (GC-MS/MS) is necessary for the compounds with lower molecular weight and less characteristic ions such as chloropropanols and acrylamide. Supplement relationship can be found between the coupled column and the GC-MS/MS method according to the applications presented in this study. The sample preparation efficiency can be improved and the polarity ranges be increased for the method by GC-MS/MS because of the separation without derivatization by coupled column. The tandem mass can produce enough ions for identity, suppress the matrix interfering and improve the sensitivity.