采用二维气相色谱及毛细管色谱柱分析汽油中苯和甲苯的含量

采用微板流路控制技术(Deans Switch)和常见的商品毛细管柱HP-5 (30 m×0.32 mm×0.25 μm)和Rtx-TCEP (30 m×0.25 mm×0.4 μm),建立了一种全新的分析车用汽油中苯和甲苯含量的二维气相色谱方法。用该方法分析汽油中0～5%的苯和0～20%的甲苯,两者校正曲线的线性关系良好,相关系数分别为0.9994和0.9999;标准样品5次重复测定的相对标准偏差均小于1.5%;车用汽油实际样品中苯和甲苯的加标回收率在96.8%～103.8%之间。车用汽油实际样品测定结果和SH/T 0713-2002标准方法测定结果一致。该方法是车用汽油中苯和甲苯含量测定的一种简便快捷、准确可靠的分析方法。     

Flow of the carrier gas in open-tubular capillary columns in temperature-programmed gas chromatography

A second-order non-linear partial different equation was derived to describe the dependence of carrier gas pressure in the column on the column distance and the time under temperature programmed conditions. This equation was solved numerically by the modified finite difference method for various column parameters. Constant inlet and outlet pressures were used as boundary conditions. The retention times calculated on assumption of a constant pressure profile along the column. Significant differences between retention times of corresponding solutes calculated by the two methods were found, especially when relatively long columns(L>50m) with small internal diameter(d<0.3mm)and high temperature program rates (r>5°/min)are used.     

Determination of lidocaine in human serum by capillary gas chromatography with surface ionization detection

A novel analytical method has been developed for the determination of lidocaine (2-(diethylamino)-N-(2,6-dimethyl)phenylacetamide) in human serum. After solvent extraction from serum the extract was analyzed by gas chromatography employing a van den Berg type solventless injector, a new sensitive and selective detector, the surface ionization detector, and a bonded phase flexible fused silica capillary column. The detection limit was ca. 30–50 ng/ml.     

Simultaneous determination of organotin,organolead, and organomercury compounds in environmental samples using capillary gas chromatography with atomic emission detection

As part of a continuing evaluation of new analytical and sample preparation techniques conducted by the US Environmental Protection Agency (EPA), the use of capillary gas chromatography with atomic emission detection (GC-AED) for the simultaneous determination of organotin, organolead, and organomercury compounds in environmental samples was investigated. Pentylmagnesium bromide was used to pentylate ionic organotin, organolead, and organomercury compounds; the pentyl derivatives were then separated by GC and determined by AED. Several important GC-AED parameters, including the type of injector inlet, carrier gas flow rate, and helium make-up gas flow rate, were optimized for the simultaneous determination of these organometallic compounds. Their minimum detectable concentrations were approximately 1.0 to 2.5 ng/mL using a 0.5-μL on-column injection. The calibration curves exhibited good linearity between 2.5 and 2500 ng/mL for organotin and organolead compounds, and between 2.5 and 10000 ng/mL for organomercury compounds.     

Oral malodor,assessed by closed-loop,gas chromatography,and ion-trap technology

A method is described for the analysis of volatile organic compounds in saliva and tongue coating samples. The techniue is based on an off-line preconcentration step by means of a closed-loop trapping system followed by gas chromatography-ion trap detection. With the closed-loop technique, the volatile organic compounds(VOCs) are released from the matrix and trapped on an adsorbent without interference of water. The VOCs are released from the adsorbent into the gas chromatograph by thermdesorption. After separation, identification of the compounds is performed by ion trap technology. By this technique 82 compounds could be demonstrated in saliva and tongue coating samples. The technique is also used to demonstrate the formation of volatile bacterial fermentation compounds when a protein substrate is added to tongue coating samples. It is considered a very promising tool in further research on oral malodor.     

High speed analysis of H2S and COS impurities in coal gas by capillary gas chromatography

There is a need for rapid, on-line, gas chromatographic analysis of trace levels of hydrogen sulfide and carbon oxysulfide in the oil-from-coal industry. In order to improve an existing method based on a polymer bed concentrator, a porous layer open tubular column, and a flame photometric detector, time-optimization of the various steps involved was attempted. Use of a redesigned concentrator, changed column operating conditions, and a photoionization detector reduced analysis times from 6.5 to 3 min and cycle times from 8 to 3 min. This could be achieved without compromising the 10 ppb detection limit required.     

Modified flame ionization detector for the analysis of large molecular weight polar compounds by capillary supercritical fluid chromatography

The modifications made to a flame ionization detector (FID) to facilitate the detection of large molecular weight polar compounds analyzed by capillary supercritical fluid chromatography are described. Some specific examples are given to demonstrate that polar compounds can be effectively eluted using deactivated fused silica capillary columns and supercritical carbon dioxide at 40°C.     

Determination of the sulfur components of gasoline streams by capillary column gas chromatography with sulfur chemiluminescence detection

A method using a sulfur chemiluminescence detector (SCD) has been developed for the qualitative and quantitative determination of sulfur components in stabilized gasoline-range process streams, including blended gasolines containing between 1 and > 4000 ppm total sulfur. The detection limit per sulfur component was approximately 50 ppb. On-column injection was employed for optimum precision and accuracy. A new probe material was found which did not soften under FID operating conditions. A new method, using a hydrogen sulfide permeation tube, was developed for rapid alignment of the probe in the FID.     

Residue analysis of organophosphorus pesticides in food with two-dimensional gas chromatography using capillary columns and flame photometric detection

Two-dimensional gas chromatography with two capillary columns of different polarity (SP 2100 and OV 225) is used for pesticide residue analysis in food samples. By means of “live chromatography” applying pneumatic switching technique according to Deans, unequivocal identification of 57 organophosphorus pesticides in food samples is achieved at trace concentrations. The instrument is equipped with only one injection port and one flame photometric detector. On-line data processing is very helpful, especially in calibration and checking the system's reliability with the multitude of test compounds. The complete pesticide residue analysis including clean-up of about six food samples can be completed by one person in 8 hours.     

Determination of chlorinated and brominated micropollutants by capillary gas chromatography coupled with on-column radio frequency plasma atomic emission detection

Capillary gas chromatography (GC) combined with on-column radio frequency plasma atomic emission detection was evaluated for the determination of polychlorinated and polybrominated biphenyls (PCBs and PBBs). Quantitation was possible utilizing a single chlorine or bromine calibration curve based on a randomly selected reference compound, because the signal per ng of halogen ranged within 17 % for 29 congeners. Combined with an internal standard to correct for potential plasma quenching from matrix components, this type of universal quantitation represented a sub-stantial simplification of current calibration procedures. In combi-nation with relatively low detection limits (1–5 pg/s of halogen), the present work suggested that GC, coupled with on-column atomic emission detection is a promising technique for the determination of halogenated micropollutants.     

Analysis of polynuclear aromatic hydrocarbons by glass capillary gas chromatography using simultaneous flame ionization and electron capture detection

The possibility of simultaneous application of an electron capture (ECD) and a flame ionization detector (FID) connected to a glass capillary column for analyzing polynuclear aromatic hydrocarbons (PNA) has been investigated. The ECD/FID ratio is determined for 46 PNA compounds. The ratios vary from 0.02 to 117 with relative standard deviations better than 20 percent determined from 10 replicate analyses. The results suggest that the method may be used for obtaining additional evidence in identifying PNA in environmental samples. Impurities and transformation products in the standard were identified by computerized glass capillary gas chromatography/mass spectrometry. Quinones and diones are responsible for the high EC-response determined in some trace components in the standard. An application of the method is shown for PNA from particulates in urban atmospheres.     

Detection of C,H, N,and O in capillary gas chromatography by atomic emission

Using a new atomic emission detector for gas chromatography, the quantitative and qualitative aspects of selective elemental detection of carbon, hydrogen, nitrogen, and oxygen were investigated. Sensitivity, precision, degree of tailing, and response variation between compounds are reported for capillary applications. Earlier atomic emission detectors reported poor sensitivity and selectivity for the analysis of oxygen. These problems have been greatly reduced due to lower interactions between elements in the sample and the silica wall of the water-cooled discharge tube. Using near-optimal sample amounts and chromatographic conditions, area precision was found to be very good with little variation in response factors among different compounds. For the compounds tested, response factors varied over a span of 2% to 3% for carbon, hydrogen, and nitrogen, and over 7% for oxygen. For quantitative analysis, area ratios were calibrated directly from the area ratios of two elements of an internal standard, and yielded better precision and compound independence than the individual calibrated response of each element. Empirical formulas were calcualted using one peak as a qualitative internal standard. Unambiguous formulas were determined for some, but not all, of the compounds tested. Further increases in precision and/or compound independence is needed before empirical formula determination can be used as a routine tool.     

Determination of the calcium entry blocker verapamil in plasma by capillary gas chromatography with on-column injection

A specific, sensitive, and accurate assay for quantitation of verapamil has been developed. The method involves a single extraction step with n-heptane, followed by evaporation at room temperature under nitrogen. 0.1 μl of the extract was injected into a capillary column coated with crosslinked 5% phenylmethylsilicone. The column separated verapamil, norverapamil, and its internal standard within 15 minutes using temperature programming from 90 to 290°C. The lower limit of detection was 1 ng/ml for verapamil. The calibration curve was linear in the concentration range (5–300 ng/ml). Plasma concentration data from dogs receiving intravenous verapamil infusion are presented.     

Assay of the nerve agent Soman in serum by capillary gas chromatography with nitrogen-phosphorus detection and splitless injection

Summary A procedure is described for the determination of the nerve agent Soman in serum. The nerve agent is separated from the serum on C₁₈ modified silica and then eluted with benzene. The concentrated sample, to which butylacetate is added, is injected splitless into a polyethylene glycol (CP Wax 57) coated fused silica column. Solvent trapping of the analytes occurs due to the added butyl-acetate. The detection is performed with a nitrogen-phosphorus detector (NPD). The determination limit of the method is 40 pg/ml.     

Determination of the isomeric distribution and associated impurities in commercial diethylbenzenes by capillary gas chromatography

A capillary gas chromatographic method for the quantitative analysis of diethylbenzene fractions is described. Estimation of ortho-, meta- and para-isomers and other C₉ and C₁₀ aromatic impurities is covered. The conditions developed involve the use of a capillary column of Carbowax-1540 (300 feet × 0.01 inch) under isothermal operation. The retention index data for a number of aromatics are presented at four temperatures (90, 100, 110 and 120°C). The method offers a good choice for any level of concentration both for isomers and impurities commonly encountered within a reasonable analysis time.     

Automated determination of nifedipine in human plasma by capillary gas chromatography with electron capture detection

A rapid, sensitive, and reliable method for the determination of nifedipine in human plasma is described. Using a single-step solvent extraction and capillary gas chromatography combined with electron capture detection, an assay sensitivity of 2 ng/ml is achieved routinely using 0.5 ml of plasma. Intact nifedipine is quantitated and separated from its nitroso- and nitropyridine-derivatives. The suitability of the assay for pharmacokinetic studies is illustrated.