New internal standard for quantitative determination of oxyphytosterols by gas chromatography

A study was conducted to develop a new internal standard for the quantitative determination of oxyphytosterols. Tests on 5-androsten-3beta,17beta-diol; 5alpha-androstan-3beta,17beta-diol; 5-pregnen-3beta,20alpha-diol; and 5alpha-pregnan-3beta,20beta-diol showed that these compounds were not fully adequate. However, the compound 3beta,22-dihydroxy-20-homo-5-pregnene, synthesized in 4 steps, resulted in a promising internal standard, with a molecule similar to hydroxysterols; retention time as trimethylsilyl in gas chromatography comprised between 5alpha-cholestane and 7alpha-hydroxycholesterol; clear mass spectrum in electronic impact mass spectrometry, with several intense ions suitable for selected ion monitoring-mass spectrometry. Further studies are necessary to observe the behavior of these compounds during the entire analytical procedure.     

气相色谱法测定氯氟吡氧乙酸十二酯的含量

建立测定氯氟吡氧乙酸十二酯含量的气相色谱(外标法)检测方法。色谱柱为二甲基聚硅氧烷毛细管柱(0.53mm×30m×1μm);柱温:初始150℃,保持3min,30℃·min-1,程序升温至270℃,保持10min;气化室温度:280℃;检测器温度:280℃;载气为氮气。测定的RSD为0.60%,回收率在95.92%~103.72%之间,线性相关系数为0.9992。该本系操作方便、快速,结果有较好重现性,能达到含量测定目的。     

The rapid quantitative determination of aromatic-type groups in gas oils by high-performance liquid chromatography

Summary A rapid method is described for the quantitative determination of aromatic-type groups in gas oil petroleum fractions. The method involves separation by high-performance liquid chromatography followed by detection with a differential refractometer, whose response to aromatic-type groups is more predictable than an ultra violet absorbance detector. A primary standard is used for calibration, and the precision and accuracy of the method have been investigated and are discussed.     

Triazolopyridine,a new derivative for the structural determination of fatty acids by gas chromatography/mass spectrometry

Triazolopyridine is proposed as a new derivative for the location of branches and double bonds in fatty acids. It is compared with previously used derivatives and found to be clearly superior to the pyrrolidide and slightly superior to the β-picolinyl ester with regard to the structure-specific fragmentation pattern. It is prepared by reacting the activated acid with 2-hydrazinopyridine followed by cyclization.     

Indirect determination of isocyanates by gas chromatography

A gas chromatographic method was developed to determine the purity of synthesized isocyanate monomers, specifically isocyanatoacrylates, and to determine the isocyanate content of synthesized polymers and prepolymers. The method is a modification of an ASTM procedure in which an isocyanate is allowed to react with excess di-n-butylamine. In the ASTM method, the amount of isocyanate present is calculated indirectly from the amount of unreacted di-n-butylamine, determined by back titration with standard hydrochloric acid. Determination of the excess di-n-butylamine by the gas chromatographic method developed has the advantages of providing better precision and requiring less sample than the titrimetric method. The two methods were compared using phenyl isocyanate as a model test compound. A synthesized monomer, methyl alpha-isocyanatoacrylate, was also analyzed, for comparison by both methods.     

Rapid ultra-trace determination of beryllium by gas chromatography

The electron capture detector has been used to measure ultra-trace quantities of beryllium separated as beryllium(II) trifluoroacetylacetonate by gas Chromatographic techniques. The lower limit of detectability is ca. 4 x 10(-13) g of beryllium. Calibration plots extend from 8 x 10(-13) to 4 x 10(-11) g of beryllium. Samples of beryllium in aqueous solution at four concentrations (1.18 x 10(-7), 1.18 x 10(-8), 2.95 x 10(-9), and 8.84 x 10(-10)g ml ) were analysed quantitatively by combining solvent extraction and gas chromatography. The distribution of beryllium during the extraction procedures was determined independently by use of radioactive beryllium-7, but the use of tracers is not required in the recommended procedure. Interference studies were made on cations and anions found in biological samples. At the concentrations used in the extraction procedure and the gas Chromatographic process, none of the fifteen ions studied interferes appreciably.     

Determination of patulin by capillary gas chromatography of the heptafluorobutyrate derivative

Formation and capillary gas chromatography of patulin heptafluorobutyrate is reported for the first time. The derivative was identified by gas chromatography-mass spectrometry (M+ = 350). Electron-capture detector response for patulin heptafluorobutyrate was linear in the range 0.05 to 0.5 ng. This sensitive and reproducible derivatization technique was applied to the determination of patulin in apple juice by capillary gas chromatography-electron-capture detection. The overall method recovery averaged 84% and less than or equal to 10 micrograms/l could be detected.     

A modified method for the determination of methylmercury by gas chromatography

A simple modification of the West?? extraction procedure for methylmercury and its determination by gas chromatography (GC) is presented. The cysteine clean-up step has been modified, with use of cysteine-impregnated paper instead of cysteine solution. Methylmercury bromide is extracted from the sample into toluene and is selectively adsorbed on the cysteine paper. Interfering compounds are washed from the paper with toluene. The isolated methylmercury is set free with sulphuric acid containing bromide, extracted into benzene and determined by GC. The modification of the extraction procedure results in good recovery and reproducibility for various biological and environmental samples, good sensitivity with a detection limit of 0.1 ng/g, avoidance of difficulties arising from emulsion formation, cleaner chromatograms, and faster analysis. It is particularly suitable for determination of low levels of MeHg.     

Rapid determination and confirmation of biogenic amines in tuna loin by gas chromatography/mass spectrometry using ethylchloroformate derivative

A gas chromatography-mass spectrometry (GC/MS) method is described for the easy rapid determination and simultaneous confirmation of the biogenic amines putrescine (PUT), cadaverine (CAD), histamine (HTA), and spermidine (SPD) in fresh frozen tuna loin. The method can also be used to monitor tyramine (TYR). The method involves homogenization of fish tissue, extraction of biogenic amines into trichloroacetic acid solution, centrifugation, alkalization, and derivatization of supernatant with ethylchloroformate. All seafood species were fortified to contain 2.5, 5.0, 10.0, 12.5, and 25.0 microg/g (ppm) PUT, CAD, and SPD; and 10.0, 20.0, 40.0, 50.0, and 100.0 microg/g (ppm) HTA. Determination was based on standard curves for each analyte using peak areas with matrix standards equivalent to a concentration range bracketing the spike level. A set of 5 matrix controls (unfortified tuna tissue) was also analyzed; only endogenous SPD was found in all samples. The interassay average recoveries ranged from 57 to 79% across analytes and spike levels.     

Plasma determination of 3-methylclonazepam by capillary gas chromatography

A capillary gas-liquid chromatographic method for the determination of 3-methylclonazepam in plasma was developed. This method involved a single extraction by butyl acetate followed by analysis of the organic extract on a CP-Sil 5 glass capillary column with detection by electron capture. The detection limit was about 0.1 ng/ml, and the inter- and intra-assay precision did not exceed 8% for the concentration range 0.1-6.0 ng/ml. Specificity towards some of the possible metabolites in human plasma was demonstrated. This method was used for the measurement of the pharmacokinetic parameters of 3-methylclonazepam in healthy volunteers after a single intravenous administration of 1 mg, and oral administrations of 1 and 4 mg.     

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.