Methods in high resolution gas chromatography. Two-dimensional techniques

Basic methodology to effect the separation of complex samples by gas chromatography is discussed from an experimental point of view. Several possibilities are presented which are commonly used to enhance the information content of a gas chromatographic run. These include incorporation of more than one set of retention data, multiple detectors, and special column switching techniques. These and other techniques have sometimes been labeled “multidimensional” in the literature. An attempt is made to define the term “two-dimensional chromatography”. The review is divided into sections which point out the different directions which have been taken to deconvolute chromatographically unresolved components. Particular emphasis is placed on technology which is capable of dealing with samples of extreme complexity, and instrumentation for trace- and ultratrace analysis is dicussed with specific examples. The future of two-dimensional techniques in gas chromatography is looked into.     

Methods in high resolution gas chromatography. Two-dimensional techniques

Basic methodology to effect the separation of complex samples by gas chromatography is discussed from an experimental point of view. Several possibilities are presented which are commonly used to enhance the information content of a gas chromatographic run. These include incorporation of more than one set of retention data, multiple detectors, and special column switching techniques. These and other techniques have sometimes been labeled “multidimensional” in the literature. An attempt is made to define the term “two-dimensional chromatography”. The review is divided into sections which point out the different directions which have been taken to deconvolute chromatographically unresolved components. Particular emphasis is placed on technology which is capable of dealing with samples of extreme complexity, and instrumentation for trace- and ultratrace analysis is dicussed with specific examples. The future of two-dimensional techniques in gas chromatography is looked into.     

Methods in high resolution gas chromatography. Two-dimensional techniques

Basic methodology to effect the separation of complex samples by gas chromatography is discussed from an experimental point of view. Several possibilities are presented which are commonly used to enhance the information content of a gas chromatographic run. These include incorporation of more than one set of retention data, multiple detectors, and special column switching techniques. These and other techniques have sometimes been labeled “multidimensional” in the literature. An attempt is made to define the term “two-dimensional chromatography”. The review is divided into sections which point out the different directions which have been taken to deconvolute chromatographically unresolved components. Particular emphasis is placed on technology which is capable of dealing with samples of extreme complexity, and instrumentation for trace- and ultratrace analysis is dicussed with specific examples. The future of two-dimensional techniques in gas chromatography is looked into.     

Recent contributions of high resolution gas chromatography to the analysis of environmental hydrocarbons

Analyses of hydrocarbon fractions from different areas of the marine environment are described to illustrate the possibilities and limitations of high resolution gas chromatography (HRGC) in the analysis of environmental samples. Examples are given of dissolved, particulate, and sedimentary hydrocarbons and organochlorine compounds; the importance of an adequate sampling of the marine environment is stressed. HR chromatographic profiles obtained in two columns of low and high polarity (SE-52 and PEG 20M) permit the sources and transport pathways of both natural and anthropogenic hydrocarbons to be traced. Analysis of tissues of marine mammals, which metabolize or excrete many of the biogenic and petrogenic hydrocarbons present in other areas of the marine environment, may provide an opportunity to obtain relatively clean profiles of many anthropogenic compounds of interest. The plotting of mass chromatograms from data compiled by COM-GC-MS remains the most appropriate method for the conclusive indentification of these compounds.     

Supercritical fluid extraction of PCBs in tandem with high resolution gas chromatography in environmental analysis

A simple method has been developed for the direct coupling of supercritical fluid extractions (SFE) with a high resolution gas chromatograph (HRGC) equipped with an electron capture detector (ECD). SFE conditions have been investigated for polychlorinated biphenyls (PCBs) from sediments in terms of mobile phase, entrainer, pressure, temperature, and mass-flow through the extractor. Dynamic leaching and static steady-state extractions were compared. Extraction efficiencies of up to 100% in less than 15 minutes have been obtained. The extracted PCBs are quantitatively transferred into a fused silica open tubular column (OTC). Determination of PCBs was tested on certified sediment from National Water Research Institute and the results agreed well with certified values.     

Chiral recognition in the resolution of enantiomers by GLC

Summary Chiral recognition of many enantiomeric solutes by a chiral amide stationary phase is based mainly on hydrogen bonding. A chiral-recognition-factor CHI is proposed, given by the difference of the enthalpy change in the enantiomer discrimination, standardized with respect to the specific interaction of the solutes with the diamide core of the stationary phase. The r?le of the entropy part is also discussed. By extrapolation of the retention behaviour to elevated temperature, peak inversion of enantiomers is predicted. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

基于不同提取方法的水稻叶片蛋白质组的二维液相色谱分离及高分辨质谱分析

建立了酚法提取-二维液相色谱分离-高分辨质谱分析水稻叶片蛋白质组的方法。水稻叶片蛋白质经过酚法提取,酶解肽段脱盐后用离线反相-反相二维液相色谱分离,然后用线性离子阱/静电场轨道阱组合式高分辨质谱分析,共鉴定到2712种蛋白质。比较了液相色谱分离系统（一维液相色谱与二维液相色谱）和水稻叶片蛋白质提取方法（酚法、十二烷基硫酸钠法（SDS法）和三氯乙酸/丙酮法（TCA/丙酮法））对鉴定蛋白质数量的影响,结果表明：在二维液相色谱条件下,酚法、SDS法和TCA/丙酮法鉴定到的蛋白质数目为2712、2415和1914,分别是一维液相色谱条件下鉴定到的蛋白质数目的2.7、2.5和1.9倍。二维液相色谱条件下,酚法鉴定到的蛋白质数目比SDS法和TCA/丙酮法分别多297和798。与SDS法和TCA/丙酮法相比,酚法不但鉴定到的蛋白质数量多,而且能够鉴定到一些极端蛋白质,如酸性、碱性及高等电点的蛋白质。此外,对二维液相色谱条件下3种蛋白质提取方法提取到的蛋白质进行生物学功能分类,发现3种方法鉴定到的蛋白质的功能存在互补性,但酚法鉴定到的蛋白质功能种类最多。该法为水稻蛋白质组学研究提供了技术支撑,同时也为其他作物的蛋白质组学研究技术提供重要的借鉴。     

Quality of high count rate high resolution short-time activation analysis

The fast transfer system was modified to enable a fixed counting geometry with high reproductibility using an endcap geometry. The optimal count rate for short time activation analysis by means of the loss free counting system was found to be within 100–140 kcts/s, if a high accuracy is needed (1%). The method of calculating the peak area after the dead time and pile up corrections was modified by changing the peak fitting parameters gradually with increasing count rates. Epithermal activation by a⁶LiD converter was found to be an ideal irradiation technique for short time activation analysis especially for heavy elements due to the lower contribution of²⁴Na and²⁸Al (up to 30 fold).     

Determination of low-level99Tc in environmental samples by high resolution ICP-MS

An analytical method has been developed for the determination of low-level⁹⁹Tc in environmental samples by High Resolution ICP-MS. The method consists of leaching of⁹⁹Tc by HNO₃ and separation by three different solvent extractions with 30% TOA-xylene, MEK, and cyclohexanone. Finally, purification of⁹⁹Tc was made by using an anion exchange resin column to reduce dissolved solids content. The final solution was adjusted to 1M HNO₃ for introducing into the HR-ICP-MS. The accuracy and precision of the method was confirmed to be satisfactory by applying this technique to the determination of⁹⁹Tc in IAEA marine algae sample (AG-B-1). Measurements of⁹⁹Tc using 0.5–2.5 g of sediment samples from the Irish Sea, UK, were successfully performed by the present method.     

Neutron activation analysis of high purity silver using high resolution gamma-spectrometry

A method of neutron activation determination of microimpurities in high purity silver has been developed. For matrix activity separation the extraction of silver by dibuthylsulfide (DBS) was employed. The purification coefficient was 10⁸ after triple extraction. Using Ge(Li) detector it was possible to determine 30 elements simultaneously in silver samples.     

Variable alignment of high resolution data by cluster analysis

High resolution time-of-flight secondary ion mass spectrometry (HR TOF-SIMS) is a powerful surface analytical method. For complex samples, this technique may yield intricate spectra that are difficult to interpret visually. Chemometric methods are useful for data analysis. However, these methods require that spectra are represented in a matrix format. Variances in mass measurements caused by calibration or instrumental effects may present difficulties in properly aligning mass spectral peaks into the correct columns of the data matrix. Cluster analysis of resolution elements is proposed as an alternative approach to construct the data matrix. An automated method for optimizing the data alignment is presented and evaluated for standard steel samples.     

GLC analysis of thiabendazole residues in citrus fruit

Analysis of thiabendazole (TBZ) residues in citrus fruit is performed using a bonded phase, SE-54, fused-silica capillary column. The fungicide is extracted with hexane: ethyl acetate (90:10, v/v) at high pH and, after a short cleanup, determined by gas-liquid chromatography with a nitrogen-phosphorus detector (NPD). Recoveries through the method are always higher than 80% and the limit of detection is 0.01 mg/Kg. TBZ residues are determined in whole fruit, peel, and pulp of "Washington Navel" oranges and "Hernandina" clementines treated with 1500 mg/L fungicide. Residues found in these samples and their changes during storage are reported. TBZ analysis in samples with high residue levels (peel and whole fruit) is also carried out by direct determination in the crude extracts. Results obtained with this shorter method are similar to those of the former proposed method.     

Chemical state analysis of Al by high resolution X-ray spectroscopy

A quantitative method for chemical state analysis of aluminum was proposed by the combination of high resolution X-ray spectroscopy and the nonlinear least square fitting method. Determination of coordination and population analysis were performed with AlV₂O₄ and clay minerals.     

Determination of nitrated-polyaromatic hydrocarbons (nitro-PAHs) in environmental samples by high resolution chromatographic techniques

An analytical procedure is described for the fractionation of organic compounds present in environmental samples and the determination of nitro polyaromatic hydrocarbons (nitro-PAHs). Both low and high resolution liquid chromatography are employed for the prefractionation of the soluble organic fraction (SOF) extracted from particulate matter or gaseous pollutants collected on adsorption traps. High resolution gas chromatography is used to analyze four fractions containing alkanes, PAHs, nitro-PAHs, and other polar PAHs. Nitrogen-containing species are separated by GC and detected specifically using an alkali flame (NPD) detector. Flame ionization (FID) detection, GC-MS of positive ions, and negative ion chemical ionization MS of the whole fraction is used for the identification and quantitation of the various components. The composition of SOF extracted from particulate matter emitted from diesel exhausts is elucidated and a large number of nitro-PAHs identified by the combination of the various techniques.     

Peak‐fitting of high resolution ToF‐SIMS spectra: a preliminary study

Peak‐fitting has been performed on a series of peaks obtained by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) analysis in order to assess whether information may be obtained from this procedure on the samples' characteristics. A variety of samples were examined including a range of treatments for aluminium leading to different surface roughnesses, polymer films with a range of polydispersities, molecular weight (MW) and thicknesses as well as aluminium samples with adsorbed adhesion promoters on the surface. Variation of peak‐fitting was assessed by varying the peak intensity, full width at half maximum (FWHM) and peak asymmetry. Although further studies are needed it is possible to say that the peak width increases with roughness whereas peak asymmetry seems to be related to oxide thickness. Polymer characteristics do not seem to influence the width whereas the peak asymmetry increases either versus MW or polydispersity. A possible assumption is that the peak asymmetry relates to the ion formation processes. Additional work with varying polymer films thickness indicates that both FWHM and peak asymmetry may be related to sample charging and this could be used for assessment of film thicknesses. Finally, peak‐fitting was used to obtain a more reliable peak area when peaks are too close in mass to use current methods. Copyright © 2009 John Wiley & Sons, Ltd.     

High resolution gas chromatography/mass spectrometry analysis of the environmental pollutants methylnitronaphthalenes

We report the linear retention indices of the 14 methylnitro-naphthalenes on three high resolution capillary columns and their electron impact mass spectra. The analyses of the methylnitro-naphthalenes in an ambient air sample by gas chromatography/mass spectrometry with multiple ion detection utilizing 5% phenylmethylsilicone, 50% phenylmethylsilicone, and smectic columns are shown.     

Ultrafast laser induced breakdown spectroscopy for high spatial resolution chemical analysis

Femtosecond laser induced breakdown spectroscopy (LIBS) was used to identify the spatial resolution limitations and assess the minimal detectable mass restrictions in laser-ablation based chemical analysis. The atomic emission of sodium (Na) and potassium (K) dopants in transparent dielectric Mica matrices was studied, to find that both these elements could be detected from 450 nm diameter ablation craters, full-width-at-half-maximum (FWHM). Under optimal conditions, mass as low as 220 ag was measured, demonstrating the feasibility of using laser-ablation based chemical analysis to achieve high spatial resolution elemental analysis in real-time and at atmospheric pressure conditions.