A simple multisensor detector based on tin dioxide in capillary gas chromatography

The use of an array of metal oxide film sensors as a detector for volatile organic compounds in capillary gas chromatography is described. The results of determination of the sensitivity, response time, and linearity range of the analytical signals from sensors are presented; these parameters are compared with similar characteristics of commercial gas chromatographic detectors. An approach is proposed to the identification of organic compounds by the shape and relative size of responses of individual sensors. It is demonstrated that the multisensor detector is applicable to solving typical analytical problems of the quantitative analysis of multicomponent mixtures.     

Determination of trihalomethanes in water samples: a review

This article reviews the most recent literature addressing the analytical methods applied for trihalomethanes (THMs) determination in water samples. This analysis is usually performed with gas chromatography (GC) combined with a preconcentration step. The detectors most widely used in this type of analyses are mass spectrometers (MS) and electron capture detectors (ECD). Here, we review the analytical characteristics, the time required for analysis, and the simplicity of the optimised methods. The main difference between these methods lies in the sample pretreatment step; therefore, special emphasis is placed on this aspect. The techniques covered are direct aqueous injection (DAI), liquid-liquid extraction (LLE), headspace (HS), and membrane-based techniques. We also review the main chromatographic columns employed and consider novel aspects of chromatographic analysis, such as the use of fast gas chromatography (FGC). Concerning the detection step, besides the common techniques, the use of uncommon detectors such as fluorescence detector, pulsed discharge photoionization detector (PDPID), dry electrolytic conductivity detector (DELCD), atomic emission detector (AED) and inductively coupled plasma-mass spectrometry (ICP-MS) for this type of analysis is described.     

Gas chromatography-optical fiber detector for the speciation of aromatic hydrocarbons in confined areas

An analytical method, based on separation with gas chromatography (GC) and detection with optical fiber (OF), was used for the separation, detection and quantification of benzene, toluene, ethylbenzene, p-xylene, m-xylene and o-xylene. The use of OF as a detector is based on the variations of the reflected optical power detected when the aromatic compounds eluted from the GC column are sorbed in a thin polymeric film on a single-mode OF. General figures of merit, such as the analytical time, analytical error and analytical performance of GC-OF were similar to those of the classical analytical methods, such as a gas chromatography-flame ionization detector (GC-FID). However, the developed GC-OF method constitutes a much less expensive alternative for the speciation of aromatic hydrocarbons compounds, with high accuracy, and being most suitable for actual monitoring work on confined environments.     

Analytical methods for phenyltin compounds in polychlorinated biphenyl-based transformer oil samples

We present the first study on the analytical methods of phenyltin compounds (PTs) in polychlorinated biphenyl (PCB)-based transformer oil samples. Tetraphenyltin (TePhT) has been used as stabilizer for some kinds of PCBs-based transformer oil formulations. Monophenyltin (MPhT), diphenyltin (DPhT) and triphenyltin (TrPhT) could have been formed from TePhT during long-term use. TePhT was directly measured by gas chromatograph (GC) connected with three types of detectors, a mass spectrometer (MS), a flame photometric detector (FPD) and an atomic emission detector (AED) after dilution with hexane. MPhT, DPhT and TrPhT were propylated with Grignard reagent before measurement. The MS was the most sensitive of the detectors, with detection limits of phenyltin compounds of 30 ng/ml (MPhT), 9.8 ng/ml (DPhT), 5.5 ng/ml (TrPhT) and 0.60 ng/ml (TePhT), respectively. From the viewpoint of selectivity, MS was slightly worse than other detectors, but interference from PCBs matrices was not significant under ordinary analytical conditions. Two used transformer oil samples were analyzed using the analytical methods developed in this study. TePhT and TrPhT were found in both samples.     

Ozone-based sulfur chemiluminescence detection: Its applicability to gas,supercritical fluid,and high performance liquid chromatography

The sensitive detection of sulfur-containing analytes is of interest in many industrial applications; selective detection is also desirable since these compounds are usually present at trace levels in difficult matrixes. The purpose of this article is to review the use of the Sievers® ozone-based sulfur chemiluminescence detector, and its coupling with gas chromatography, supercritical fluid chromatography, and high performance liquid chromatography. Detection limits, linearity, response factors, and selectivity are discussed for each of these techniques. Critical operational parameters for the SCD are also described. The use of other sulfur selective detectors for SFC and HPLC is also briefly summarized.     

Comparison of the response of four aerosol detectors used with ultra high pressure liquid chromatography

The responses of four different types of aerosol detectors have been evaluated and compared to establish their potential use as a universal detector in conjunction with ultra high pressure liquid chromatography (UHPLC). Two charged-aerosol detectors, namely Corona CAD and Corona Ultra, and also two different types of light-scattering detectors (an evaporative light scattering detector, and a nano-quantity analyte detector [NQAD]) were evaluated. The responses of these detectors were systematically investigated under changing experimental and instrumental parameters, such as the mobile phase flow-rate, analyte concentration, mobile phase composition, nebulizer temperature, evaporator temperature, evaporator gas flow-rate and instrumental signal filtering after detection. It was found that these parameters exerted non-linear effects on the responses of the aerosol detectors and must therefore be considered when designing analytical separation conditions, particularly when gradient elution is performed. Identical reversed-phase gradient separations were compared on all four aerosol detectors and further compared with UV detection at 200 nm. The aerosol detectors were able to detect all 11 analytes in a test set comprising species having a variety of physicochemical properties, whilst UV detection was applicable only to those analytes containing chromophores. The reproducibility of the detector response for 11 analytes over 10 consecutive separations was found to be approximately 5% for the charged-aerosol detectors and approximately 11% for the light-scattering detectors. The tested analytes included semi-volatile species which exhibited a more variable response on the aerosol detectors. Peak efficiencies were generally better on the aerosol detectors in comparison to UV detection and particularly so for the light-scattering detectors which exhibited efficiencies of around 110,000 plates per metre. Limits of detection were calculated using different mobile phase compositions and the NQAD detector was found to be the most sensitive (LOD of 10 ng/mL), followed by the Corona CAD (76 ng/mL), then UV detection at 200 nm (178 ng/mL) using an injection volume of 25 μL.     

Evaluation and comparison of selective gas chromatographic detectors for the analysis of pesticide residues

Summary A series of studies is described on the evaluation and comparison of some selective gas chromatographic detectors used in pesticide residue analysis. A detailed study of the optimization and response characteristics of the CsBr and RbCl three-electrode alkali flame ionization detector for N and P compounds, the Coulson electrolytic conductivity detector in the nitrogen, sulphur and pyrolytic modes of operation and the sulphur phosphorus emission detector, a type of flame photometric detector, was carried out to obtain maximum sensitivity and reliability for the analysis of pesticide residues in various biological substrates. It was observed that the alkali flame and electrolytic conductivity detector responses to nitrogen compounds were of the same order, while the electrolytic conductivity detector was more sensitive than the flame photometric detector to sulphur compounds. Also, attempts were made to correlate the responses from these different detector systems using the insecticide chlorpyrifos which contains P, S, Cl and N atoms. The use of chlorpyrifos as an evaluation standard in verifying the acceptable performance of these types of detectors is recommended.Chemistry and Biology Research Institute Contribution No 901     

Sulfur and nitrogen chemiluminescence detection in gas chromatographic analysis

Sulfur and nitrogen compounds exist in a wide variety of analytical samples, from harmful contaminants in refinery streams to important ingredients in certain beverages, spices and condiments. Accurate determination of sulfur/nitrogen concentrations in these diverse samples is very important for process monitoring, quality control, product development, as well as basic research in these different industries. Due to the complex nature of the matrices, and the fact that the sulfur/nitrogen analytes usually exist at low concentrations, an element-selective detector for sulfur/nitrogen is indispensable to the GC analysis of these samples. To meet this challenge, sulfur and nitrogen chemiluminescence detectors for GC have become one of the most powerful tools available to analytical chemists, thanks to their high sensitivity, selectivity and equimolar detector response. In this brief review, an overview of the chemiluminescence detector operating principles, as well as the detector characteristics is presented. Examples of their applications in petroleum refinery, environmental analysis and food/flavor industry are presented. The two chemiluminescence detectors have also been combined into one convenient package and an example of applications of the simultaneous sulfur/nitrogen chemiluminescence detector is also provided.     

A new way of using thermal conductivity detectors in capillary gas chromatography

Summary Large volume TCD cells, as commonly used in gas chromatographs, can be used as detectors in capillary gas chromatography without loss of separation efficiency and sensitivity, by expanding the column effluent. This can be achieved by inserting a throttle between the column and the detector cell and reducing the pressure in the cell. A device working at a cell pressure of 20 mbar was studied to determine its usefulness for practical analytical work. The construction of the detector is described. The results of measurements concerning the linearity, sensitivity and accuracy of the detector, when used with glass capillary columns are given.     

Capillary Electrophoresis Coupled On-Line with Inductively Coupled Plasma Atomic Emission Spectrometry for Elemental Speciation

Capillary electrophoresis (CE) has become a powerful analytical technique for the separation of a variety of analytes ranging from small inorganic ions to large biomolecules such as proteins and nucleic acids. A selective and sensitive detector for CE has been one of the most important and challenging prerequisites for the growth of CE. On-column UV-Vis detectors are commonly used to determine the analytes separated by CE. However, these detectors are often not very selective. Other detection techniques such as mass spectrometry, laser induced fluorescence, amperometry, and inductively coupled plasma spectrometry have been investigated to provide a more sensitive and selective detection for the target analytes. However, relatively few studies have been published on the use of inductively coupled plasma atomic emission spectrometry (ICP-AES) as a means of detection in CE separation.     

Effects of contamination on ion mobility detection after gas chromatography

The ion mobility detector is a device that can be used for the selective, ultratrace detection of organic compounds after capillary gas chromatography. It is the only gas chromatographic detector which does not require heteroatomic compounds for selective response, yet concern is often expressed over its quantitative capabilities. Being a secondary ionization device, competitive charge transfer reactions from unseparated compounds or detector gas contamination may decrease the accuracy of measurement. This paper investigates the effects of both electronegative and electro-positive contaminants on the detector's response. In general, it was found that contamination of the detector did affect response but no more severely than in conventional detectors such as the electron-capture detector or the flame ionization detector.     

Review of recent developments and applications in low-pressure (vacuum outlet) gas chromatography

The concept of low pressure (LP) vacuum outlet gas chromatography (GC) was introduced more than 50 years ago, but it was not until the 2000s that its theoretical applicability to fast analysis of GC-amenable chemicals was realized. In practice, LPGC is implemented by placing the outlet of a short, wide (typically 10–15 m, 0.53 mm inner diameter) analytical column under vacuum conditions, which speeds the separation by reducing viscosity of the carrier gas, thereby leading to a higher optimal flow rate for the most separation efficiency. To keep the inlet at normal operating pressures, the analytical column is commonly coupled to a short, narrow uncoated restriction capillary that also acts as a guard column. The faster separations in LPGC usually result in worse separation efficiency relative to conventional GC, but selective detection usually overcomes this drawback. Mass spectrometry (MS) provides highly selective and sensitive universal detection, and nearly all GC-MS instruments provide vacuum outlet conditions for implementation of LPGC-MS(/MS) without need for adaptations. In addition to higher sample throughput, LPGC provides other benefits, including lower detection limits, less chance of analyte degradation, reduced peak tailing, increased sample loadability, and more ruggedness without overly narrow peaks that would necessitate excessively fast data acquisition rates. This critical review summarizes recent developments in the application of LPGC with MS and other detectors in the analysis of pesticides, environmental contaminants, explosives, phytosterols, and other semi-volatile compounds.     

Comparison of a gas chromatography-optical fibre (GC-OF) detector with a gas chromatography-flame ionization detector (GC-FID) for determination of alcoholic compounds in industrial atmospheres

An analytical methodology based on an optical fibre detector coupled to gas chromatograph has been developed for the speciation of some volatile alcoholic compounds. This methodology combines the separation capability of gas chromatography with an optical fibre detector made of an optical fibre sensitized with a thin polymeric film of poly[methyl(3,3,3-trifluoropropyl)siloxane] (PMTFPS). The response of the detector has been characterized at 650 nm for nine different alcohols (allyl alcohol, n-propyl alcohol, sec-butyl alcohol, isobutyl alcohol, n-butyl alcohol, isoamyl alcohol, methyl isobutyl carbinol, cyclohexanol and diacetone alcohol). An alternative method based on gas chromatography-flame ionization detector (GC-FID) was also used in order to evaluated the performance and compare the analytical results with the proposed method. The time of analysis, the analytical error and the analytical performance were similar for both methods. However, the analytical apparatus based on the GC-OF detector is much less expensive than the GC-FID and show high accuracy and suitability for actual monitoring on indoor atmospheres.     

Analytical Methods for Speciation of Organotins in the Environment

The growing awareness over the environmental fate of organotin compounds is reflected in the large number of analytical methods developed for their separation. Organotin compounds have varying degrees of toxicological properties, depending on the nature and number of alkyl groups bonded to the tin atom. Most of the analytical speciation methods applied to actual environmental media have involved prior derivatization to transform organotin compounds into volatile hydrophobic analytes amenable to separation and identification by gas chromatography coupled to a sensitive and selective tin-detector. Evidence exists that members of the same homologous series are related by environmental degradation pathways. Chemical treatment prior to analysis, or high temperatures associated with gas chromatography separation, may alter the relative amounts of organotins in samples and blur the true environment picture. To avoid species redistribution that may occur during derivatization or gas speciation analysis, methods based on liquid chromatography and supercritical fluid chromatography have been investigated. This review documents analytical methods for determination of tin and speciation of organotin compounds, in the hope that it will be of value to those interested in initiating a programme for assessing the impact of such species on the environment.     

生物体系中硒代氨基酸的手性形态分析进展

综述了近年来利用高效液相色谱法（HPLC）、气相色谱法（GC）以及毛细管电泳（CE）等分析手段与其它高灵敏检测器联用对生物体系中硒代氨基酸进行手性形态分析研究情况，参考文献40篇。     

Hyphenation and hypernation the practice and prospects of multiple hyphenation

In the past two decades, combining a chromatographic separation system on-line with a spectroscopic detector in order to obtain structural information on the analytes present in a sample has become the most important approach for the identification and/or confirmation of the identity of target and unknown chemical compounds. In most instances, such hyphenation can be accomplished by using commercially available equipment. For most (trace-level) analytical problems encountered today, the combination of column liquid chromatography or capillary gas chromatography with a mass spectrometer (LC–MS and GC–MS, respectively) is the preferred approach. However, it is also true that additional and/or complementary information is, in quite a number of cases, urgently required. This can be provided by, for example, atomic emission, Fourier-transform infrared, diode-array UV–vis absorbance or fluorescence emission, or nuclear magnetic resonance spectrometry. In the present review, the various options are briefly discussed and a few relevant applications are quoted for each combination. Special attention is devoted to systems in which multiple hyphenation, or hypernation, is an integral part of the setup. As regards this topic, the relative merits of various combinations—which turn out to include a mass spectrometer as one of the detectors in essentially all cases—are discussed and the fundamental differences between GC- and LC-based systems are outlined. Finally, the practicability of more extensive hypernation in LC, viz. with up to four spectrometers, is discussed. It is demonstrated that, technically, such multiple hyphenation is possible and that, from a practical point of view, rewarding results can be obtained. In other words, further research in this area is certainly indicated. However, in the foreseeable future, using several separate conventional hyphenated systems will be the commonly implemented solution in most instances.     

Detectability enhancement of spectrophotometric detectors by the use of multidimensional gas chromatography

Multidimensional gas chromatography (2D GC) is demonstrated as a way to improve limits of detectability of spectrophotometric detectors. UV and IR detectors are generally less sensitive than mass spectrometers or other GC detectors. This has placed some limitations on the useful capabilities provided by spectrophotometric detectors, such as the ability to provide structure‐related information for a particular analyte. In this paper, we report results from interfacing a 2D GC instrument to a UV detector. Symmetry factor and the ratio of retention time divided by peak width did not show deterioration of the quality of chromatography when a megabore column was used with this detector. Furthermore, an increase in the limits of detectability over that attainable in a single‐column system was realized by using the 2D GC system. However, the low flow (1 mL/min) imposed by the use of a microbore column (250 μm ID) caused significant tailing when the UV detector was used.     

燃油燃料含硫化合物形态分布剖析技术研究进展

介绍了目前用于燃油、燃料(如汽油、柴油、煤油、喷气燃料)的硫化物形态分布剖析的多种分析技术,包括电化学方法和气相色谱与多种选择性检测器联用的方法(如GC - FPD、GC - AED、GC - SCD、GC - MS等),并对各种分析技术的研究现状进行了概述.     

Photometric and electrochemical detection of purine and pyrimidine compounds in reversed-phase and ion-exchange high-pressure liquid chromatography

An investigation of the optimal conditions for the determination of selected purine and pyrimidine compounds has been made by studying the separation efficiency of reversed-phase columns and ion-exchange columns and comparing the sensitivity of photometric and electrochemical detectors. The combination of ion-exchange HPLC with electrochemical detection proved very good for the separation of electroactive compounds, under the experimental conditions studied. Both types of column allow detection at the picomole level. In general the electrochemical detector appears to be the more sensitive of the two types.     

Detector Systems in Capillary Gas Chromatography

Expressions for the minimum detectable amount Q_o and the minimum analyte concentration C_o as functions of the chromatographic parameters are derived for both mass and concentration sensitive detectors. The effects of pressure drop, column inner diameter, and film thickness are given. The minimum analyte concentration for mass flow sensitive detectors, C_o^m, can be reduced considerably by selecting the carrier gas velocity well above its optimum value (related to H_min), however, at the cost of long columns and long analysis times. For Q_o the improvements can be neglected, and so the analysis can best be performed at u_opt. When the flow rate in the detector, F_d, is equal to the column flow rate F_c, the maximum permissible detector volume of concentration sensitive detectors is proportional to d_c² up to d_c³, and so narrow bore columns require detectors of extremely small volume. Make-up gas has to be added when the actual volume is too large, thus worsening the detectability. Another approach, vacuum operation of the detector cell, appears to be very attractive. On the other hand, when wide bore columns are used in combination with small volume concentration sensitive detectors, very small values of Q_o^c and C_o^c are obtainable when the abundant carrier gas can be removed before entering the detector cell. Digital noise filtering can further reduce the obtainable Q_o and C_o values, especially for broad peaks and thus for wide bore columns.