Determination of amino acids by gas chromatography using a wide bore capillary column

A procedure is described in which a wide bore capillary column is used as an alternative to the more traditional packed column for the quantitative analysis of amino acids as their N-heptafluorobutyryl isobutyl ester (HBB) derivatives. The column, installed in a gas chromatograph previously configured for use with a packed column, is shown to give good reproducibility by repeated determination of amino acid response factors (RSD values for all amino acids are below 3%). A number of problems, encountered during the use of this column, are discussed and suitable techniques to overcome them are reported.     

Dynamic headspace capillary gas chromatography: A versatile analytical technique

The applicability of dynamic headspace analyses for viscous liquids and solid samples is demonstrated. Some comments on the usefulness of this technique for quantifying volatiles in polymeric matrices are made.     

Dynamic headspace analysis of solid waste materials

A dynamic headspace stripping technique for the extraction of volatile organic compounds has been applied to a variety of solid and semisolid waste materials. A simple glass apparatus accommodates a wide range of sample sizes and allows for the volatiles to be stripped at elevated temperatures. Concentration on Tenax, followed by thermal desorption and analysis by fused silica capillary gas chromatography provides detailed information on the volatile content of waste samples of widely differing matrix composition.     

Rapid determination of oligomeric hindered amine light stabilizers in polymeric materials

Hindered amine light stabilizers are essential for the stabilization of synthetic polymers, particularly for materials used for outdoor applications. Although up to now a considerable number of studies dealing with the analytics of this class of stabilizers had been published, especially the determination of oligomeric hindered amine light stabilizers is still an analytical challenge. In the current work, a fast and simple liquid chromatographic method for the quantitative determination of oligomeric hindered amine light stabilizers is presented. A key aspect of this method is their completely different retention behavior depending on the pH, enabling a single peak elution approach by a pH gradient run. This allows a quantitation with simple UV detection independent of the actual oligomeric composition. Calibration curves within the concentration range relevant for the analysis of real polymer samples (LOQ = 70 mg/L) were constructed with R ² values above 0.99. Spiked extracts from polyolefin samples showed recovery rates between 97.3 and 102.9% for five different commercial hindered amine light stabilizers. Relative standard deviations were between 2.0 and 3.9%. Furthermore, it was demonstrated that the employed approach can be easily adapted for mass spectrometry detection.     

Analysis of headspace samples using off-line sorbent trapping coupled with automated thermal desorption and splitless injection onto a cryogenically cooled wide bore capillary column

Gas chromatographic equipment and procedures are described for automated splitless injection of pseudo-static headspace samples collected externally onto a sorbent trap. The GC microprocessor controls, in sequence, carrier gas backflushing of the sorbent trap for water removal, splitless thermal desorption into a cryogenically cooled wide bore (0.53 mm i. d.) capillary column and oven temperature programming. The method has been routinely applied for profiling the mid-to-high boiling compounds (bp 80–225°C) in the headspace of a variety of foods and beverages. Method criteria, advantages and limitations are discussed. FID and NPD chromatograms for brewed coffee and peanut butter volatiles are presented as typical examples.     

Classification of polymer batch variations by dynamic headspace/capillary gas chromatography/multivariate data analysis

Gas chromatographic profiles have been generated from different batches of a polypropylene/polyethylene copolymer. The profiles generated from polymer pellets have been obtained by dynamic headspace/capillary gas chromatography analysis. Initially 10 to 40 peaks were chosen at random from the quantitative reports and transferred to a data table. After appropriate scaling the table has been analyzed by a multivariate statistic program, SIMCA (Soft Independent Modeling of Class Analogy) a pattern recognition technique. The method has been used to differentiate batches according to sensory qualities of the final packaging product and changes in polymer peilet production.     

Gas chromatography of plasma amino acids using a wide bore column: Comparison with packed and capillary columns

A procedure is described in which a wide bore glass capillary column is used as an alternative to the more traditional packed column in the analysis of amino acid levels in plasma. The coefficients of variation for all amino acids (with the exception of aspartic acid) were better than 11% with recoveries ranging from 81% to 122%. The data are compared with the corresponding results obtained using a packed column and show significant differences (p < 0.005) between values for glycine, serine, isoleucine, proline, methionine, aspartic acid, phenylalanine, and lysine. A similar comparison between results from the wide bore and the fused-silica open tubular (FSOT) column shows better agreement. Adjustment of chromatographic conditions for the wide bore analysis yields results in good agreement with those from FSOT analysis but which still differe significantly from the backed column data.     

The performance of various capillary columns for the analysis of volatile flavor compounds in dairy products by dynamic headspace gas chromatography

The aim of this study was to test the suitability and performance of various stationary phases and column dimensions for dynamic headspace gas chromatography of food aromas. The trials were performed using an aqueous test mixture containing thirty seven volatile flavor components of intense aroma, and a sample of ripe Swiss Emmental cheese. The best performance with both samples was obtained with a capillary column coated with a thick film of polydimethylsiloxane. This column resolved the greatest number of compounds in the cheese sample and resulted in the overlapping of one pair of peaks only from the test mixture. Because of its other advantages, i. e. high capacity owing to its film thickness, and insensitivity to the high moisture content of some samples or traces of oxygen in the carrier gas, the polydimethylsiloxane column appears suitable for the analysis of the volatile and highly polar compounds present in complex mixtures such as food aroma.     

Considerations of speed and efficiency in capillary gas chromatography

The analysis time for a given resolution is a complex function of stationary phase selectivity, column radius, and thickness of the stationary phase film. Variation of these parameters has a large effect not only on analysis time, but also on the column inlet pressure and other instrumental requirements. The minimum amount that can be reliably detected as well as the maximum sample capacity of a column are strongly related to the selected column dimensions.     

Multiple headspace extraction-capillary gas chromatography (MHE-CGC) for the quantitative determination of volatiles in contaminated soils

A multiple headspace extraction-capillary gas chromatographic method for the quantitative, accurate, and rapid determination of volatiles in multicontaminated soil samples has been developed. A thick film fused silica column has been used and a nine-step multiple headspace extraction (MHE) determination performed. Calibration was achieved by introducing 1 μl of a standard solution of mixed volatiles into empty headspace vials, the presence of the matrix being unnecessary in multiple headspace extraction. Accuracy of determination by MHE-CGC and a simple method employing standard additions have been compared.     

顶空气相色谱法测定化妆品中15种挥发性有机溶剂残留

建立了化妆品中15种挥发性有机溶剂残留的顶空气相色谱测定方法。样品经60 ℃、30 min静态顶空后,采用气相色谱-氢火焰离子化检测器进行检测,外标法定量。加标回收试验结果表明: 15种挥发性有机溶剂残留平均回收率为62.8%～116%,相对标准偏差均小于5%。方法的检出限为0.09～0.68 mg/kg。该方法可有效克服基体干扰,一次进样可同时分离和测定化妆品中15种挥发性有机溶剂,准确灵敏,简单快速,适用于化妆品中挥发性有机溶剂残留的检测。     

Possibilities of dynamic headspace analysis coupled with capillary GC for the investigation of solid samples

The advantages of the dynamic headspace method for the analysis of solid samples, as compared with the static head space method, are discussed. Examples of dynamic headspace analyses are given to illustrate its possibilities.     

Preparation,evaluation, and comparison of wide bore (320 μm) and narrow bore (50 μm) cyanosilicone-coated capillary columns for gas chromatography

The preparation of wide bore (320 μm) and narrow bore (50 μm) fused silica capillary columns is described for immobilized cyanopropyl substituted silicones containing 60 and 88% substitution. The effect of high temperature deactivation with cyanopropylcyclosiloxanes was studied with a special test mixture. Curing was achieved with dicumyl peroxide or azo-tert-butane. The columns were evaluated and compared in terms of efficiency, activity, polarity, and temperature stability. Different coating methods were compared for the narrow bore columns. The activity of the 60% cyanopropyl columns that had been immobilized with dicumyl peroxide was significantly larger than for azo-tert-butane immobilized columns. The polarity of polar columns appeared to depend greatly on column temperature and is completely different for wide and narrow bore columns.     

Quantitative determination of volatiles in polyolefins by dynamic headspace/capillary gas chromatography/mass spectrometry

The possibilities of quantitative dynamic headspace by use of a multiple extraction method and an internal gas standard system for various classes of organic compounds in polyethylene and polypropylene are demonstrated. Numerous compounds can be analyzed over wide ranges of concentration and vapor pressure. However, the present study shows that the precision of the desorption parameters is of critical importance for assuring good quantitative results. The possibilities of using a theoretical model are also described. The recovery may be determined and the use of repeated desorption cycles can be reduced.     

Dynamic headspace enrichment/reinjection for open tubular GC/FTIR analysis of volatiles in polymers

An analytical system for the analysis of volatiles entrained in polymers is described. This system is based on a thermal desorption oven connected to a cold trap. After enrichment of headspace vapor, trapped material is reinjected and analyzed by open tubular gas chromatography/Fourier transform infrared spectroscopy, OTGC/FTIR. The thermal desorption oven is designed to provide different modes of sample introduction: use of a pyroprobe; insertion of a piece of quartz tubing with applied sample; or syringe injection. Headspace enrichment is carried out in a piece of fused silica capillary tubing filled with glass beads. The trap may be cooled either electrically using Peltier elements or with liquid nitrogen. A six-port rotary valve is used for flow switching between enrichment and reinjection modes. All system parameters, temperatures, and timed events, are controlled from the gas chromatograph. Dynamic headspace analysis is demonstrated as a method for polymer characterization.     

顶空毛细管气相色谱法测定茶多酚中有机溶剂的残留量

建立了顶空毛细管气相色谱法测定茶多酚中正己烷、氯仿、乙酸乙酯和丙酮4种有机溶剂残留量的方法.并讨论了平衡温度、平衡时间、盐效应对测定的影响.分析结果表明:该方法对上述4种有机溶剂均达到了完全分离,相关系数为0.994～0.999,检出限范围为0.065～0.268 μg/g,测定结果的相对标准偏差为0.39%～2.13%,样品的回收率为90.9%～105.3%.     

顶空进样-气相色谱法检测乳制品中硫氰酸盐的含量

建立了顶空进样气相色谱法测定乳制品中硫氰酸盐含量的方法。乳制品中硫氰酸盐用水提取,然后用乙酸锌溶液沉淀蛋白质,将提取液离心,取上清液加入氯胺T将硫氰酸离子衍生为氯化氰,顶空进样,经BP10(14%氰丙基苯基聚硅氧烷)气相色谱柱分离,电子捕获检测器(ECD)检测,外标法定量,同时对衍生剂用量、顶空加热时间和保温温度进行了优化。结果表明: 硫氰酸盐在0.005～0.1 mg/L内线性关系良好,相关系数(r)为0.997,定量限(以信噪比(S/N)≥10计)为0.1 mg/kg。在1.0、2.0、10.0 mg/kg 3个添加水平下进行了回收率和精密度试验,加标回收率为90.0%～110.0%,相对标准偏差(RSD, n=10)为4.98%～7.89%。该方法操作简便、快速、稳定性好,可用于乳制品中硫氰酸盐的测定,能满足日常检测要求。应用该法对市售的18种乳制品进行了检测,发现所测乳制品皆含有硫氰酸盐,含量大约在0.5～10 mg/kg。     

Detection of volatile organic sulfur compounds in water by headspace gas chromatography and membrane inlet mass spectrometry

Two gas chromatographic methods, GC-FID (flame ionization detection) and GC-ELCD (electrolytic conductivity detector) are compared in tlie analysis of volatile organic sulfur compounds (VOSCs) in water samples with a membrane inlet mass spectrometry (MIMS) technique. Carbon disulfide, ethanethiol, dimethyl sulfide, ethyl-methyl sulfide, thiophene, and dimethyl disulfide were used as test compounds. Linear dynamic ranges were found to be two decades with the GC-ELCD method and four decades with the GC-FID and MIMS methods. Detection limits were at low (μg/1 levels with the two gas chromatographic methods and clearly below μg/1 level with the MIMS method. Analysis of one sample takes 40 min with the gas chromatographic methods and five minutes with the MIMS method. The selectivity was good, especially with the GC-ELCD and the MIMS method. In addition, quantitative results obtained with spiked water samples by the three methods are compared.     

Determination of volatile chlorinated hydrocarbons in water samples by static headspace gas chromatography with electron capture detection

A simple, efficient, solvent‐free, and commercial readily available approach for determination of five volatile chlorinated hydrocarbons in water samples using the static headspace sampling and gas chromatography with electron capture detection has been described. The proposed static headspace sampling method was initially optimized and the optimum experimental conditions found were 10 mL water sample containing 20% w/v sodium chloride placed in a 20 mL vial and stirred at 50ºC for 20 min. The linearity of the method was in the range of 1.2–240 μg/L for dichloromethane, 0.2–40 μg/L for trichloromethane, 0.005–1 μg/L for perchloromethane, 0.025–5 μg/L for trichloroethylene, and 0.01–2 μg/L for perchloroethylene, with coefficients of determination ranging between 0.9979 and 0.9990. The limits of detection were in the low μg/L level, ranging between 0.001 and 0.3 μg/L. The relative recoveries of spiked five volatile chlorinated hydrocarbons with external calibration method at different concentration levels in pure, tap, sea water of Jiaojiang Estuary, and sea water of waters of Xiaomendao were in the range of 91–116, 96–105, 86–112, and 80–111%, respectively, and with relative standard deviations of 1.9–3.6, 2.3–3.5, 1.5–2.7, and 2.3–3.7% (n = 5), respectively. The performance of the proposed method was compared with traditional liquid–liquid extraction on the real water samples (i.e., pure, tap, and sea water, etc.) and comparable efficiencies were obtained. It is concluded that this method can be successfully applied for the determination of volatile chlorinated hydrocarbons in different water samples.