Tandem technique

The combination of chromatography and mass spectrometry (MS) is a subject that has attracted much interest over the last forty years or so. The combination of gas chromatography (GC) with mass spectrometry (GC-MS) was first reported in 1958 and made available commercially in 1967. Since then, it has become increasingly utilized and is probably the most widely used hyphenated or tandem technique, as such combinations are often known. The acceptance of GC-MS as a routine technique has in no small part been due to the fact that interfaces have been available for both packed and capillary columns which allow the vast majority of compounds amenable to separation by gas chromatography to be transferred efficiently to the mass spectrometer. Compounds amenable to analysis by GC need to be both volatile, at the temperatures used to achieve separation, and thermally stable, i.e. the same requirements needed to produce mass spectra from an analyte using either electron (El) or chemical ionization (Cl) (see Chapter 3). In simple terms, therefore, virtually all compounds that pass through a GC column can be ionized and the full analytical capabilities of the mass spectrometer utilized. 

Tandem technique An alternative term for the combination of two or more analytical techniques. 

R.P.W. Scott, Tandem Techniques, John Wiley Sons, Ltd, Chichester (1997). 

Post-chromatographic and tandem techniques LC/MS, LC/NMR, and chromatographic data handling (Chapters 19-21)... 

As a result of advances in detection technology, newer HPLC detection techniques may be utilized. For example, evaporative light-scattering detection and refractive index detection may be used to quantify impurities with poor or no UV chromophore. Conductivity detection may also be used. In some cases, when no chromophore is present, chemical derivatization may be used to add a chromophore. Increasingly, tandem techniques such as liquid chromatography mass spectrometry (LC-MS) and GC-MS are utilized for impurity characterization. The highly selective nature of LC-MS ensures that few impurities are undetected. 

Combination of ADMET with other well-known polymerization techniques has yielded new materials with interesting thermal behaviors. Further use of tandem techniques in this type of materials synthesis can be useful for creating hybrid materials unattainable through conventional methods. 

In terms of gross morphology, characteristically, coca leaf has two lines which run parallel to the mid-rib on the underside of the leaf. Taxonomically, however, it is difficult to identify leaf and plant material to species on the basis of morphology (leaf and fiower structure) alone and indeed hybridization between species is common [5]. In order to establish that the material comes from the genus Erythroxylon and contains controlled substances, it is therefore necessary to demonstrate the presence of cocaine. In bulk (those which can be seen by the naked eye) samples, this is achieved through a good physical description of the materials and packaging, followed by a combination of presumptive tests, TLC and a tandem technique, usually GC-MS. 

Gas chromatography-mass spectrometry The combination of gas chromatography with mass spectrometry see also Tandem technique). 

Hyphenated technique The combination of two analytical techniques (see also Hybrid technique and Tandem technique). 

Analytical instrumentation continues to increase in sophistication, and as a consequence, the range of materials that can now be almost routinely analysed has increased accordingly. Books in this series which are concerned with the techniques themselves will reflect such advances in analytical instrumentation, while at the same time providing full and detailed discussions of the fundamental concepts and theories of the particular analytical method being considered. Such books will cover a variety of techniques, including general instrumental analysis, spectroscopy, chromatography, electrophoresis, tandem techniques. 

A final comment on tandem techniques. For routine analytical work with forensic overtones, tandem systems can be essential. For the ad hoc occasion when solute confirmation is necessary, fraction collection followed by the usual spectroscopic examination will often give results that will be at least as reliable and probably more precise. In addition, the equipment will certainly be less expensive to purchase and maintain. 

Stationary phases, detection devices, etc. However, advances in instrumentation were not the only important factor in the development of analytical methods for essential oils in plants. Sample extraction and concentration were also improved. The most outstanding improvements in the determination of the composition of essential oils came from the introduction of tandem techniques involving prior/further chromatography or spectroscopy. The great amount of information on the application of GC and hyphenated techniques to essential oils has led to much research in this field, and to the pubhcation of... 

Scott, R. R W., Tandem Techniques, John WUey Sons, New York, 1984. 

The development of methods for ionising molecules that are far less drastic than the traditional route of vaporising them, and then bombarding them with electrons from an electron gun, has enabled the mass spectra of underivatised carbohydrates to be studied. Moreover, tandem techniques have enabled ions to be selected, made to undergo collision-induced dissociation by the presence of an inert gas such as argon or helium and the fragments examined. The... 

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