GC/MS combination

In a GC/MS combination, passage of the separated components (A, B, C, D) successively into the mass spectrometer yields their individual spectra. 

Mass-spectral (MS) Analysis. Mass spectral analyses were obtained using a computerized Finnigan Model 1015 gas chromatograph-mass spectrometer (GC-MS) operated at 70 eV. Samples were introduced via direct insertion probe or by utilizing the GC-MS combination, both operated over a programmed temperature range. 

Chemical analysis of odorants in ambient air is hampered by the presence of a plethora of volatile organic compounds, which do not contribute to the odour. Nevertheless application of either powerful separation and identification techniques, such as the GC-MS combination, or specific GC-detection or absorption procedures allow qualitative and quantitative determination of odourants. Improvements are under way to achieve the sensitivity necessary for relevant immission concentrations, which go down to 0.1 ppb for some odorants. 

The best sensitivity for 1,2-dibromoethane quantification is obtained by either electron capture detector (ECD) or Hall electrolytic conductivity detector (HECD) in the halide detection mode, since these detectors are relatively insensitive to nonhalogenated species and very sensitive to halogenated species. Another common detection device is a mass spectrometer (MS) connected to a GC. The GC/MS combination provides unequivocal identification of 1,2-dibromoethane in samples containing multiple components having similar GC elution characteristics (see Table 6-2). To date, GC equipped with either ECD or HECD has provided the greatest sensitivity for detecting... 

GC-MS combines high separation efficiency and reproducibility due to the stable ionization achieved by electron impact (El), and is one of the most... 

Unfortunately, the LC-MS combination is less successful. In part, this may be due to technological interfacing problems, but even if these are solved, LC-MS is unlikely to provide the same degree of universality (large molecules will remain a problem), spectral information and reproducibility as the GC-MS combination. For the moment, the combination of LC with a multichannel UV absorption detector is a more realistic proposition. 

The development of hyphenated techniques has depended on advances in at least three areas interfacing, scanning speed of the measuring technique, and adequate data systems. The different combinations of chromatography and on-line measuring instruments have different requirements, but a few generalizations can be made. Since the GC/MS combination is the most popular and successful, it will be described as a typical example of the types of considerations required for interfacing instruments. Problems associated with other interfaces will be mentioned briefly later. 

The LC-MS setup initially pursued closely resembled the successful GC-MS combination. Interfaces were developed to remove (most of) the mobile phase prior to the introduction of the analytes into the mass spectrometer. Early examples of this... 

Gas chromatography-mass spectrometry (GC-MS) combination has become one of the most important coupling in analytical chemistry used for the confirmation of results obtained by other detectors [9]. This technique is based on the fragmentation of the molecules that arrives into the detector. Ion formation occurs and they are separated by the... 

The compounds are representatives for different types of pollutants. 11 halogenated aliphatic hydrocarbons are determined using capillary GC equipped with electron capture detector. The remaining pollutants, representing both basic/neutral and acidic compounds are determined using GC/MS combined with an automated search computer program. 

Other methods of quantitative analysis, which are much more accurate and applicable to wider ranges of mixtures, include GC, mass spectrometry (MS), the GC-MS combination, in which products separated by GC are detected by MS, infrared spectroscopy, specific sensors to measure water, sulfur dioxide, etc., and all other appropriate techniques, which may include wet chemical analytical methods. 

The first member of this class identified in a coffee flavor, and even in food, was 5-acetyl-2-methylox-azole (L.23) found by Stoffelsma and Pypker (1968) and Stoffelsma et al. (1968) but without mention of a reference compound. An intensive study on the presence of oxazoles in coffee aroma was conducted somewhat later by Vitzthum and Werkhoff (1974a,b). A coffee extract was obtained by steam distillation, enriched by adsorption/desorption and extracted with dilute hydrochloric acid. The compounds in this basic fraction were identified by classical GC/MS combination, among them 20 oxazoles in concentrations of the order of 1-10 ppb. The reference standards were prepared or purchased and their NMR spectra were measured. 

Gas chromatography-mass spectrometry (GC-MS) combines the separating power of GC with the uniquely powerful detection capabilities of MS (Figure 3.38). With this coupled technique, it is possible to separate, identify and quantify components in a mixture. As this is quite an established hyphenated technique, there is a choice of mass spectrometric ionisation techniques and analysers available to couple with GC. 

Numerous additional advances in GC/MS occurred throughout the last decade. Mass spectrometers have now become almost routine, reliable instruments. Improvements in design of both sector and quadrupole instruments is today reflected in greater spectral resolution and sensitivity parameters. Versatility of the GC/MS combined instruments has been dramatically improved by better interfacing techniques and an increased use of capillary columns. The chemical ionization methods have become important for work with relatively unstable molecules there is a significant rationale for their increasing use in biochemical research. 

The choice of carrier gas is sometimes dependent on the detector in use, as is the case, for example, with the thermal conductivity cell, the electron capture detector, or in GC/MS combination. For an optimum performance of certain detectors (dependent on either the principle or a particular design), an extra gas must be added at some point between the column end and the point of detection. Such make-up gas arrangements are particularly common in capillary GC. 

Mass spectrometer (MS) [S] sales have always been high, especially since MS is the principal detector in a number of hyphenated techniques such as GC-MS, MS-MS, and LC-MS. The GC — MS combination accounts for about 60% of MS sales since it is used widely in drug and environmental testing. Innovations in interface technology such as inductively coupled plasma (ICP)-MS, FC-MS and thermospray or particle beam interfaces for LC-MS have both advanced the technology and expanded the interest in applications. Recent introductions of lower cost MS instruments with automated sampling and computerized data analysis have added to the attraction of the technique for first-time users. 

It is possible to add on another technique to analyse the components once they are separated out from a mixture using GC. GC-MS combines gas chromatography with mass spectrometry (MS). The previously unknown organic components of a mixture are separated... 

LC is a suitable technique for trace analysis of organic micropollutants. However, the separation power of common LC columns is insufficient for very complex mixtures. Online couphng of LC with MS will be an attractive tool for analysis of low-volatility organic compounds in samples. Howeveg cleanup of the sample prior to LC-MS analysis will be very necessary. The sensitivity is less than that obtained by capillary GC-MS combinations and at present there is no universal LC-MS system for all types of compounds. 

GC-MS combines the advantages of both techniques the high resolving power and the speed of analysis of GC is retained, while the MS provides both positive identification and quantitative analyses down to the ppb level. Mass ranges of 10 to 600 Daltons are common for low cost systems, and up to 1000 Daltons for more expensive systems. Costs range from 40K up to 75K for simple bench-top systems. 

Coal liquids are complicated mixtures. Separation of different compound types by liquid chromatography (LC) prior to MS analysis is a common practice. LC-MS, using both quadrupole and magnetic sector mass spectrometers, was applied to analyze aromatic fractions of coal tars, and the results were also compared with GC-MS and the above GC-MS combination methods. The molecular weight range observed by LC-MS was much greater than that observed by GC-MS and was similar to those observed by GC-MS combination methods. 

Elucidation of Drug Metabolites by Means of a GC-MS Combination Fresenius Z. Anal. Chem. 279(2) 135-136 (1976) CA 84 173498f... 

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