Stimultaneous quantitative analysis using dual capillary columns of different polarities

Complex organic mixtures, such as coal liquefaction and oil shale products and by-products, are comprised of hundreds or thousands of individual components. State-of-the-art high resolution gas chromatography does not always provide sufficient resolution to allow accurate quantitation or identification of many compounds of interest. The concept of dual capillary column chromatography combines the different resolving characteristics of two capillary columns coated with different stationary phases into a single chromatographic run. In this approach, both columns are connected to the same injection port. Analysis of complex mixtures in this fashion can confirm the identification and quantitation of components on two columns of different polarity with little increased analysis time, can provide a means of obtaining quantitative data for individual components which are known to coelute on any one column, and can alert one to unknown coelution problems that would be undetected by gas chromatographic analysis on a single capillary column. Simultaneous dual column analysis was applied to three samples, the neutral polycyclic aromatic hydrocarbon (PAH) fraction of a Solvent Refined Coal-II (SRC-II) heavy distillate, the nitrogen-containing polycyclic aromatic compound (N-PAC) fraction of an SRC-II heavy distillate, and the basic fraction from a shale oil process water. Fused silica capillary columns coated with SE-54 and Durawax 3 were used for the analyses of the heavy distillate, while SE-54 an Carbowax 20M capillary columns were used for the analysis of the process water.     

Enhancement of the static SIMS secondary ion yields of lipid moieties by ultrathin gold coating of aged oil paint surfaces

Static secondary ion mass spectrometry (SIMS) is a powerful technique for identification and localization of pigments and binding media present in traditional paintings. Coating the surface of a cross‐section with a 20 Å thick gold layer improves the yields of secondary ions from the fatty acids and diacids. A chalk tablet containing 1% stearic acid, which was partially covered during gold deposition, is used as a test system to investigate the increase of the organic secondary ion yields upon gold deposition in SIMS imaging. A comparative study of a native and gold‐coated aged surface of a lead white‐containing linseed oil paint demonstrates the enhancement of the organic ion yields on a sample relevant for painting studies. The yields of oil paint‐derived negative ions increase by a factor of 3 whereas the yields of positive ions increase by a factor of 2–4. The different types of charged functional groups determine the degree of improvement in yield. Gold coating improves the ionization process of the fatty acids and does not influence their fragmentation. The dissociation of the lead white by the primary ion beam is reduced due to the gold coating. Copyright © 2004 John Wiley & Sons, Ltd.     

Chemical Constituents of the Essential Oil of <Emphasis Type="Italic">Nepeta oxyodonta</Emphasis>

Water-distilled essential oil from the aerial parts of Nepeta oxyodonta Boiss. was analyzed by GC/MS for the first time. Fifty-eight components were identified. The major components were (E)-caryophyllene (12.6%), spathulenol (8.5%), β-bourbonene (8.1%), germacrene-D (7.4%), α-cadinol (7.3%), germacrene-D-4-ol (6.8%), T-cadinol (5.6%), and caryophyllene oxide (5.3%).__________Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 141–142, March–April, 2005.     

南瓜籽烘烤前后化学成分的分析

对烘烤前后南瓜籽中的化学成分进行分析并对比。采用同时蒸馏萃取装置萃取南瓜籽中的挥发性成分,采取超临界CO2萃取技术萃取南瓜籽油脂,并将其分为酸、碱、中性三个部分,用气相色谱-质谱联用方法分析其中化学成分并进行对比。结果表明,南瓜籽挥发性成分中含有多种醛类和酯类化合物,烘烤后产生了大量的烷基吡嗪,其在碱性部分中的相对含量比烘烤前提高14倍多,不饱和醛类化合物含量也有明显提高。南瓜籽油脂中的主要化学成分是油酸、亚油酸及其酯类。还含有生物活性功能成分如植物甾醇、角鲨烯和维生素E等。烘烤后除角鲨烯含量有所降低,维生素E、植物甾醇、亚麻酸等均有提高。     

On-line coupling of liquid chromatography,capillary gas chromatography and mass spectrometry for the determination and identification of polycyclic aromatic hydrocarbons in vegetable oils

Summary An on-line combination of liquid chromatography, gas chromatography and mass spectrometry has been realized by coupling a quadrupole mass spectrometer to an LC-GC apparatus. Liquid chromatography was used for sample pretreatment of oil samples of different origin. The appropriate LC fraction, containing polycyclic aromatic hydrocarbons, was transferred to the gas chromatograph using a loop-type interface. After solvent evaporation through the solvent vapour exit and subsequent GC separation, the compounds were introduced into the mass spectrometer for detection and identification. The GC column was connected to a short piece of deactivated fused silica that protruded into the ion source. The total analytical set-up allowed the direct analysis of oil samples after dilution in n-pentane without any sample clean-up. Detection limits are about 40 pg in the full scan mode and about 1 pg with selective ion monitoring, i.e. 20 ppb and 0.5 ppb respectively.     

An improved method for determination of light hydrocarbons in stabilized crude oil

Summary This paper reports a quick, and simple method for quantitative determination of C₂ to C₆ hydrocarbons in stabilized crude oil without using a back flush system. A mixture of crude oil and internal standard is injected into a GC equipped with a 6 meter length of fused silica capillary as a guard column. The light hydrocarbons are separated individually up to the last peak of the hexane group with the heavier components trapped in the guard column. The total analysis time for each sample is 15 minutes. The base line is table for up to 15 consecutive analyses. The guard column and the injector port are then reconditioned by simply heating them for one hour at 300 °C.     

Improved method for the determination of sulfur components in natural gas

Determination of trace concentrations of sulfur components in natural gas is a true analytical challenge. Only analytical procedures based on gas chromatography can meet the sensitivity and accuracy requirements dictated by environmental regulation institutions and modern chemical industry. In the present contribution the sample pretreatment and chromatographic separation steps have been evaluated and optimized based on the use of a flamebased sulfur chemiluminescence detector (SCD) for target compound detection. The proposed instrument consists of a programmed temperature vaporizing (PTV) injector employing a liner packed with Chromosorb 104, a 4 μm thick film apolar column and a flame-based SCD. Using a 13 mL sample loop the detection limit achievable with the new method is 3 μg S/m³. The precision of replicate measure. ments is generally in the range of 5–15% relative standard deviation. Lower detection limits can be achieved by preconcentrating larger sample volumes, e.g. 100 mL.     

Chemical Composition of the Essential Oil of Rosmarinus officinalis Cultivated in the Algerian Sahara

The volatile compounds obtained by hydrodistillation of the aerial parts of Rosmarinus officinalis cultivated at the Algerian Sahara were analyzed by GC/MS. Thirty compounds were characterized representing 98.2% of the essential oil with 1,8-cineole (29.5%), 2-ethyl-4,5-dimethylphenol (12.0%) and camphor (11.5%) as the major components.     

Fatty Acid Composition of Pistachio Nuts in Turkey

In this study oil yields and fatty acid compositions in the kernels of two varieties (Uzun and Siirt) of pistachio grown in different region of Turkey were investigated. Kernel oils were obtained by Soxhlet extraction using petroleum ether. The yields were found to be 57.1-58.9% and 56.1-62.6 respectively for the Uzun and Siirt varieties, on a moisture-free basis. Fatty acid composition of oils were analysed by GC/MS in the methyl ester form. Fourteen fatty acid components representing about 99% of the total oils were characterised. Oleic acid (55.4-62.6% and 60.7-65.5%, respectively) was the main fatty acid component in both varieties. Pentadecanoic acid, (Z)-7-hexadecenoic acid, margaric acid, Z-7-octadecenoic acid, arachidic acid, 11-eicosenoic acid, and behenic acid were detected in both varieties for the first time.     

Multivariate comparison of concentration profiles in materials analysis

Hierarchical cluster analysis (HCA) and principal components analysis (PCA) were applied to find groups between similar depth-profiles in thin-layers investigated by Rutherford backscattering spectrometry (RBS).HCA yields in one run an objective hierarchy of similarity for several profiles. Among the similarity coefficients examined the linear measure, the Euclidean distance and the exponential measure respond with different sensitivity to overall shifts in direction of the concentration axis, whereas the correlation measure relates to parallelism of the profiles.For agglomerative HCA with Euclidean distance, a lowest significant linkage level has been defined by use of Fisher'sF-test. For divisive HCA based also on Euclidean distance, the maximum of a separating function marks the most separating cluster step. The outcomes of both proposals agree for the data set investigated.PCA is useful for verifying the results of HCA and yields additional information about the data structure. In the actual example quite different positions of features (concentrations at definite depths) in the space of the two first principal components hint at peculiarities during the metallurgical coating process.