A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems

Vejrosta, J., Novák, J. and Jönsson, J.Å., 1982. A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems. Fluid Phase Equilibria, 8: 25–35.A method has been developed for measuring the partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems, based on the direct analysis of both phases. A gas mixture containing a known proportion of a volatile compound is drawn through the liquid (water) until equilibrium is established. A defined volume of the liquid phase is then withdrawn through a porous-polymer trap while maintaining the system at equilibrium. The residual water in the trap is then expelled by a stream of nitrogen gas, and the deposit remaining is thermally desorbed and analyzed by gas chromatography. This approach, together with an experimental technique for producing gas mixtures containing an accurately known concentration of hydrocarbon at low values, makes it possible to determine accurately the partition coefficients of low-solubility compounds, such as for hydrocarbons in aqueous systems, at very low solute concentrations in the system. The method has been verified by measuring the partition coefficient of hexane between the gas and liquid phases of an aqueous system at various concentrations and temperatures.     

Determination of absorption efficiencies of carbon dioxide absorbents by gas chromatography

An HP-5880A gas chromatograph equipped with FID has been used to determine the efficiency of various CO(2) absorbents and some molecular sieves. Temperature, the CO(2) concentration in the absorbed gas mixture and space velocity of the gas mixture have effects on the absorption efficiency to different degrees, but temperature is a controlling factor. It has been established that in gas analysis the systematic errors arising from CO(2) impurities in the carrier gas are negligible when CO(2) is absorbed by carbon dioxide absorbents. Three methods for eliminating blank error are presented. The differential volume method through preconcentrating at the same time but at different flow-rates (DVMST) is proposed as the best method in preconcentration analysis. With the preconcentration technique, the minimum detectable level for CO(2) in a 10-litre sample is around 0.3 ppb(v/v).     

Detailed hydrocarbon analysis of gasoline by GC-MS (SI-PIONA)

A gas chromatographic – mass spectrometric (GC-MS) method has been developed for detailed analysis of the hydrocarbon content of gasoline. The method is equipped with special software and includes the analysis of oxygenated compounds in a single run. The technique utilizes three basic components: the separating power of high resolution capillary gas chromatography, a mass spectrometer with a controllable ion source and ion fragmentation ratios, and unique software for data handling and preparation of reports. The C₄ to C₁₂ range of hydrocarbons in gasoline is covered by the method. A sample of unleaded gasoline from a gas station was analyzed without sample preparation. The results are discussed.     

Direct coupling of a gas-liquid separator to an ion mobility spectrometer for the classification of different white wines using chemometrics tools

The potential of a vanguard technique as is the ion mobility spectrometry with ultraviolet ionization (UV-IMS) coupled to a continuous flow system (CFS) have been demonstrated in this work using a gas phase separator (GPS). This vanguard system (CFS-GPS-UV-IMS) has been used for the analysis of different types of white wines to obtain a characteristic profile for each type of wine and their posterior classification using different chemometric tools. Precision of the method was 3.1% expressed as relative standard deviation. A deep chemometric study was carried out for the classification of the four types of wines selected. The best classification performance was obtained by first reducing the data dimensionality by principal component analysis (PCA) followed by linear discriminant analysis (LDA) and finally using a k-nearest neighbour (kNN) classifier. The classification rate in an independent validation set was 92.0% classification rate value with confidence interval [89.0%, 95.0%] at 95% confidence level.The same white wines analyzed using CFS-GPS-UV-IMS were analyzed using gas chromatography with a flame detector (GC-FID) as conventional technique. The chromatographic method used for the determination of superior alcohols in wine samples shown in the Regulation CEE 1238/1992 was selected to carry out the analysis of the same samples set and later the classification using appropriate chemometrics tools. In this case, strategies PCA-LDA and kNN classifier were also used for the correct classification of the wine samples. This combination showed similar results to the ones obtained with the proposed method.     

Gas chromatography/mass spectrometry versus liquid chromatography/fluorescence detection in the analysis of phenols in mainstream cigarette smoke

A new gas chromatographic/mass spectrometric (GC/MS) technique for the analysis of hydroxybenzenes (phenols) in mainstream cigarette smoke has been developed. The technique allows the measurement of 24 individual compounds, and the sum of a few other alkyl-dihydroxybenzenes. A critical evaluation is done for the new technique and for an established high-performance liquid chromatographic (HPLC) technique reported in the literature for the analysis of hydroxybenzenes in cigarette smoke, which uses fluorescence detection. Compared with the HPLC procedure, the new technique has similar accuracy, precision, and robustness. However, the GC/MS procedure allows for a larger number of phenols to be analyzed simultaneously, and eliminates any potential interference that may appear in the HPLC method. Using the GC/MS analysis, it was found that besides the main phenols typically measured in mainstream cigarette smoke such as phenol, catechol, hydroquinone, and cresols, many other phenols that are present at lower levels can be quantitated in mainstream cigarette smoke.     

用高场非对称波形离子迁移谱技术快速检测二乙醇胺

采用高场非对称波形离子迁移谱(FAIMS)对二乙醇胺(DEA)进行快速检测分析, 以热解析法进样, 确定了二乙醇胺的离子特征信号, 并与气相色谱-质谱联用仪的检测结果进行了比较. 用聚四氟乙烯(PTFE)扩散管进样, 控制二乙醇胺样品气(DEA与空气的混合气)浓度, 利用FAIMS对不同浓度的二乙醇胺样品气进行检测. 通过对离子特征信号进行量化和重复性分析, 确定了二乙醇胺样品气的检出限为0.02 μg/L, 并建立了FAIMS检测二乙醇胺样品气的离子电流强度积分面积与样品气浓度关系曲线. 为FAIMS应用于现场快速检测二乙醇胺提供了一定的依据.     

Determination of polysulphides in blood by gas chromatography and gas chromatography-mass spectrometry.

A sensitive and simple method to determine polysulphides in human blood, using an extractive alkylation technique and gas chromatography, has been devised. Polysulphides were alkylated with pentafluorobenzyl bromide, and then converted into bis(pentafluorobenzyl)disulphide by desulphuration with potassium cyanide. The disulphide was analysed qualitatively by mass fragmentography and quantitatively by gas chromatography with electron-capture detection. The lower limit of detection was 0.005 mumol/ml. Field testing in a suicide case confirmed the validity of the method.     

Development of a screening method for cocaine and cocaine metabolites in urine using solvent microextraction in conjunction with gas chromatography

A simple, quick and inexpensive screening method for cocaine and cocaine metabolites has been developed. Drug extraction was achieved using the relatively new technique of solvent microextraction (SME). Complete analysis is achieved in 13 min, using, a 6-min extraction with a 2-microl drop followed by separation on a gas chromatograph. The developed procedure was tested as a screening method for cocaine and cocaine metabolites in spiked urine samples. Using SME, concentrations as low as 0.125 microg ml(-1) of cocaine, ecgonine methyl ester, cocaethylene and anhydroecgonine methyl ester were measurable with relative standard deviation values averaging 9.0%.     

Chromatographic determination of total hydrocarbons in ethanolamine employed in sweetening process of natural gas

Summary A rapid and easy gas chromatographic method is proposed for the determination of condensate content in monoethanolamine employed in the sweetening process of natural gas in the petroleum industry. This method covers a wide range of heavy hydrocarbons (condensate) content by using a short conventational column. A comparative study has been carried out and the advantages of the gas chromatographic technique have been demonstrated.     

Application of plasma gas modulation technique for improvement of the measurement of Mn emission intensity in ICP-AES

A phase-sensitive detection technique associated with a digital lock-in amplifier was applied for an improvement of the detection in ICP-AES. The lock-in amplifier works as an extremely narrow band pass filter. It can pick up the modulated signal, which has the same frequency as the reference signal, from any noise and thus it can improve the signal-to-noise ratio. Modulation of the ICP can be performed by mixing small amounts of air to argon as the outer gas cyclically, because the emission intensities of ionic lines are enhanced by using the mixed gas. An electromagnetic valve, which is placed in the outer-gas flow path, causes periodic variation in the air gas in the outer-gas flow, and thus switching the valve on/off can modulate the ICP. By choosing the appropriate conditions, the addition of air gas enhances the emission intensity of ionic lines more than that of the background, thus leading to improved signal-to-background ratios. At the same time the lock-in amplifier further enhances the ionic emissions because it picks up only the modulated part of the signal. By applying the plasma gas flow modulation technique the detection and the determination limits of the Mn II 257.610 nm line are improved in comparison with the conventional method. A change in plasma shape corresponding to the modulation frequency is observed when the ICP is modulated.     

Rapid analysis of free medium-chain fatty acids and related ethyl esters in beer using SPE and HRGC

A modification of a procedure by Hage [1] is proposed for the gas chromatographic evaluation of the content of free medium-chain fatty acids and related ethyl esters in beer. The method involves extraction of free fatty acids and ethyl esters by SPE using C₁₈ bonded phase columns, derivatization of free fatty acids and related ethyl esters with diazomethane, and GC analysis using an SP-2340 capillary column. The results obtained have shown the method to be rapid and highly reproducible. The technique has been compared with other methods used for determination of free fatty acids.     

The determination of tertiary dodecyl mercaptan by low thermal mass gas chromatography-dual plasma sulfur chemiluminescence detection

Tertiary dodecyl mercaptan (TDM) is commonly used as a chain transfer agent in the manufacturing process of styrene/butadiene latex for use in carpet and paper industries. A gas chromatographic technique has been successfully developed for the measurement of TDM based on its sulfur content for material identification, trend analysis, or for the monitoring of un-reacted residual material in final products. The method employs low thermal mass gas chromatography (LTM-GC) and a dual-plasma sulfur chemiluminescence detector (DP-SCD) to attain a high degree of sensitivity and selectivity. Using the technique described, a detection limit in the range of 0.5 ppm (v/v) TDM and less than 1 min analysis time can be achieved. Response is linear over four orders of magnitude with high degree of repeatability of less than 5% RSD.     

Application of plasma gas modulation technique for improvement of the measurement of Mn emission intensity in ICP-AES

A phase-sensitive detection technique associated with a digital lock-in amplifier was applied for an improvement of the detection in ICP-AES. The lock-in amplifier works as an extremely narrow band pass filter. It can pick up the modulated signal, which has the same frequency as the reference signal, from any noise and thus it can improve the signal-to-noise ratio. Modulation of the ICP can be performed by mixing small amounts of air to argon as the outer gas cyclically, because the emission intensities of ionic lines are enhanced by using the mixed gas. An electromagnetic valve, which is placed in the outer-gas flow path, causes periodic variation in the air gas in the outer-gas flow, and thus switching the valve on/off can modulate the ICP. By choosing the appropriate conditions, the addition of air gas enhances the emission intensity of ionic lines more than that of the background, thus leading to improved signal-to-background ratios. At the same time the lock-in amplifier further enhances the ionic emissions because it picks up only the modulated part of the signal. By applying the plasma gas flow modulation technique the detection and the determination limits of the Mn II 257.610 nm line are improved in comparison with the conventional method. A change in plasma shape corresponding to the modulation frequency is observed when the ICP is modulated.     

A new approach for fast, simultaneous NO/NO2 analysis: application of basic features of multiphoton-induced ionization and dissociation of NOx

A new method of simultaneously recording NO and NO2 concentrations in complex gas mixtures is described. This method is based on resonance enhanced multiphoton ionization (REMPI), on time-of-flight mass analysis, and on monitoring the kinetic energy released upon dissociation of NO2. Its benefits are high speed and high flexibility. NO/NO2 analysis can therefore be combined with the simultaneous monitoring of other components. For instance, NH3 is a compound of interest when studying the chemical reactions of NO(x) in catalytic converters of combustion engines. The spectroscopic excitation schemes used for this new method are discussed in detail. Its reliability has been demonstrated by performing measurements at an industrial motor test facility. This novel technique performs well in comparison with conventional NO(x) analysis using chemiluminescence detection.     

Determination of polychlorinated biphenyls by neutron activation and gamma ray spectrometry

A new method for the determination of polychlorinated biphenyls in transformer oils has been developed. It is based on neutron activation of chlorine in a nuclear reactor and its determination by gamma ray spectrometry. Any organic chlorides present must be purged by volatilization. The method has been tested by analyzing 38 samples of transformer oil by gas chromatography and by this technique. Each time the concentration of chlorine was higher than 38 ppm, the oil was found to be contaiminated by the PCBs. This method provides a fast and cost effective analysis of transformer oils.     

Simultaneous analysis of gaseous and particulate sulfur in the atmosphere by X-ray fluorescence spectrometry

An analytical technique for the simultaneous measurement of the atmospheric concentrations of SO₂ gas and sulfur absorbed by aerosol particles has been developed. Aerosol particles are collected on membrane filter and at the same time SO₂ gas is captured on alkali impregnated filter. The sulfur content in each filter is measured by an energy dispersive X-ray fluorescence spectrometer consisting of a Si(Li) semiconductor detector connected to a multichannel pulse height analyzer and an excitation source of⁵⁵Fe. Two methods are acceptable for the determination of the sulfur content in impregnated filter by X-ray fluorescence analysis. In the first method X-ray fluorescence analysis is made after the collected sulfur has diffused and distributed uniformly enough throughout the filter, and in the second method X-ray fluorescence analysis has to be finished before the diffusion of the collected sulfur becomes appreciable. Some results of simultaneous analysis of SO₂ gas and particulate sulfur in the atmosphere are presented.     

Air flow assisted ionization for remote sampling of ambient mass spectrometry and its application

Ambient ionization methods are an important research area in mass spectrometry (MS) analysis. Under ambient conditions, the gas flow and atmospheric pressure significantly affect the transfer and focusing of ions. The design and implementation of air flow assisted ionization (AFAI) as a novel and effective, remote sampling method for ambient mass spectrometry are described herein. AFAI benefits from a high extracting air flow rate. A systematic investigation of the extracting air flow in the AFAI system has been carried out, and it has been demonstrated not only that it plays a role in the effective capture and remote transport of charged droplets, but also that it promotes desolvation and ion formation, and even prevents ion fragmentation during the ionization process. Moreover, the sensitivity of remote sampling ambient MS analysis was improved significantly by the AFAI method. Highly polar and nonpolar molecules, including dyes, pharmaceutical samples, explosives, drugs of abuse, protein and volatile compounds, have been successfully analyzed using AFAI-MS. The successful application of the technique to residue detection on fingers, large object analysis and remote monitoring in real time indicates its potential for the analysis of a variety of samples, especially large objects. The ability to couple this technique with most commercially available MS instruments with an API interface further enhances its broad applicability.     

湿地温室气体气相色谱分析及采样-进样技术研究进展

总结了近年来湿地温室气体通量研究的国内外现状,介绍了中科院成都生物研究所高原湿地温室气体监测的样品采集和分析技术的研究成果,并对湿地温室气体色谱分析采样-进样技术的改进展开了探讨.拟研制开发一种全新的采样-进样技术,以提高样品分析的速率和准确性,拓展色谱技术在生态环境领域的适用范围.     

Rapid analysis of coke oven gas by capillary gas chromatography

A porous layer open tubular (PLOT) column has been used for monitoring the light hydrocarbons and permanent gases produced in coking plants. The method, which offers a simple alternative to traditional multi column techniques, entails a single injection on to a Carboplot 007 capillary column and simultaneous thermal conductivity and flame ionization detection. The simplified approach proposed is restricted to coke oven gas analysis: application to other gas mixtures has not been considered. The reliability of this procedure compares favorably with that of traditional methods; the technique is also much less time-consuming: seven individual gases can be determined on-line every fifteen minutes. Primary and secondary gas standards were used to determine response curves for the gases. The method also facilitates reliable calculation of heat values associated with the burning of the fuel gas mixtures.