Gas chromatography linked to mass spectrometry

The technique of gas chromatography linked to mass spectrometry is an important tool in the study of volatile insect substances and also for the study of their biosynthesis. The subject of linked chromatographic-mass spectrometric methods, and the newer techniques that can be achieved with mass spectrometry are beyond the subject of this book. We can expect to see much wider use of high resolution mass spectrometry in the study of enzymes and biosynthetic pathways. 

Gas-chromatography coupled to mass spectrometry (G.C.-M.S.) was carried out on Rexco and Kuwait branched/cyclic fractions with a Pye IOU chromatograph (WCOT glass-capillary column coated with OV-1) on a Varian MAT hh spectrometer (with SS kk computer) at 70 eV ionization voltage. For Turkish Montan wax and asphaltite, G.C.-M.S. were run with the eutectic packed column on an MS 50 spectrometer. Field-desorption (F.D.) M.S. for Kuwait and Rexco samples were recorded on a Varian CH5D spectrometer (calibrated with perfluorkerosene) linked to a Varian Spectro-system 100 data output. 

Some destructive techniques require a thousandth of a gram while some need less than a millionth of a gram. One particularly useful combination of techniques is gas chromatography (GC) linked to mass spectrometry (MS), which together can separate the components of a complex mixture and identify all of them. In M S, molecules in the gaseous state are ionized and then exposed to an electric field. This accelerates them to a speed that enables a magnetic field to deflect them and the extent to which they are deflected depends on the atomic mass of the particle which thereby reveals its constituent atoms, from which its molecular structure can then be deduced. 

Gonzalez-Rodriguez, J., Garrido-Frenich, A., Arrebola, F. J., and Martinez-Vidal, J. L., Evaluation of low pressure gas chromatography linked to ion-trap tandem mass spectrometry for the fast trace analysis of multiclass pesticide residues. Rapid Commun. Mass Spectrom., 16, 1216-1224, 2002. 

Gas chromatography combined with mass spectrometry was used for identifying the volatile components. The analysis was carried out with a Shimadzu GC-17A linked with a Shimadzu QP-5050 at an MS ionization voltage of 70 eV, accelerating voltage of 1500 V, and ion source temperature of 250°C. The GC column was DB-Wax fused-silica capillary type (60 m x 0.25 mm i.d., 0.25 pm film thickness J W Scientific, Folsom, CA, USA). The column temperature was programmed from 70°C (2 min hold) to 100°C at a rate of 2°C/min. The column was cleaned by heating to 230°C before each run. The injector temperature was 250°C, and helium was used as the carrier gas at a flow rate of 0.8 ml/min. An oil sample of 0.2 pL was injected at a split ratio of 1 50. 

The need to understand the fate of pesticides in the environment has necessitated the development of analytical methods for the determination of residues in environmental media. Adoption of methods utilizing instrumentation such as gas chro-matography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), liquid chromatography/tandem mass spectrometry (LC/MS/MS), or enzyme-linked immunosorbent assay (ELISA) has allowed the detection of minute amounts of pesticides and their degradation products in environmental samples. Sample preparation techniques such as solid-phase extraction (SPE), accelerated solvent extraction (ASE), or solid-phase microextraction (SPME) have also been important in the development of more reliable and sensitive analytical methods. 

Pyrolysis-Gas Chromatography-Mass Spectrometry. In the experiments, about 2 mg of sample was pyrolyzed at 900°C in flowing helium using a Chemical Data System (CDS) Platinum Coil Pyrolysis Probe controlled by a CDS Model 122 Pyroprobe in normal mode. Products were separated on a 12 meter fused capillary column with a cross-linked poly (dimethylsilicone) stationary phase. The GC column was temperature programmed from -50 to 300°C. Individual compounds were identified with a Hewlett Packard (HP) Model 5995C low resolution quadruple GC/MS System. Data acquisition and reduction were performed on the HP 100 E-series computer running revision E RTE-6/VM software. 

Behavioral bioassays are inextricably linked with chemical studies to decipher the information content of olfactory signals (Albone 1984). As a complement to the experimental approach described above, several research groups have applied chemical approaches, particularly gas chromatography and mass spectrometry (GC-MS),... 

In the past decade, eight inherited disorders have been linked to specific enzyme defects in the isoprenoid/cholesterol biosynthetic pathway after the finding of abnormally increased levels of intermediate metabolites in tissues and/or body fluids of patients (Table 5.1.1) [7, 9, 10]. Two of these disorders are due to a defect of the enzyme mevalonate kinase, and in principle affect the synthesis of all isoprenoids (Fig. 5.1.1) [5]. The hallmark of these two disorders is the accumulation of mevalonic acid in body fluids and tissues, which can be detected by organic acid analysis, or preferably, by stable-isotope dilution gas chromatography (GC)-mass spectrometry (GC-MS) [2]. Confirmative diagnostic possibilities include direct measurement of mevalonate kinase activities in white blood cells or primary skin fibroblasts [3] from patients, and/or molecular analysis of the MVK gene [8]. 

The gas chromatograph is particularly useful when it is linked to a mass spectrometer. This combination is called gas chromatography-mass spectrometry (GC-MS). 

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