Gas chromatography with mass spectroscopy

Because the analyte she is after, peanut residue, is organic, the analytical method of choice for our forensic chemist will probably be GCMS, which stands for gas chromatography with mass spectroscopy. In this technique, the material is separated into its components using chromatog-... 

US EPA published its initial list of 187 organic compounds found in US drinking water in 1975. Analyses were performed using GC-MS (gas chromatography with mass spectroscopy) and a packed column to separate organic compounds. Present-day analyses using a capillary column to separate compounds have increased the resolution of GC-MS detection several fold (7). 

Principles and Characteristics The most commonly used and widely known technique coupled to gas chromatography is mass spectroscopy. In early couplings, with packed GC columns being the major problem encountered, elimination of the carrier gas at relatively high flow-rates (25mLmin 1), resulted in a significant loss of sensitivity. With the advent of open tubular devices, the column flow could be passed directly into the mass spectrometer. GC-MS is typically... 

In 2002 extensive kinetic and product studies on the reactions of gaseous Hg with molecular and atomic halogens (X/X2 where X = Cl, Br) were performed at atmospheric pressure (750 1 Torr) and room temperature (298 1 K) in air and N2 [24]. Kinetics of fhe reactions with X/X2 were studied using both relative and absolute techniques. Cold vapour atomic absorption spectroscopy (CVAAS) and gas chromatography with mass spectroscopic detection (GC-MS) were the analytical methods applied. The measured rate constants for the reactions of Hg with CI2, Cl, Br2, and Br were (2.6 0.2) x IQ-i , (1.0 0.2) x 10" , < (0.9 0.2) x and (3.2 0.3) x 10 cm molecule s , respectively. Thus CI2 and Br2 are not important reactants in the troposphere for the CI2 and Br2 concentrations reported in literature [24]. 

The hydrolysis of Alq3 was characterized with a gas chromatography and mass spectroscopy (GC-MS) apparatus modified with a headspace accessory designed to study volatile products evolved from solid materials (illustrated in Fig. 3.2, inset).41 Powder or film (deposited on foil) samples of Alq3 were held in a constant-temperature injection port for a given time, and the eluents at the end of the heating period were fed to the GC column. The relative areas of water and Hq peaks were used to measure the conversion (a typical trace is shown in Fig. 3.2). The prepurified Alq3 samples were allowed to absorb an equilibrium amount of water from the atmosphere, which occurred in about 3 min for the samples used.16... 

All hydrogenation experiments were carried out at atmospheric pressure in a reactor, consisting of a flask attached to a burette filled with mercury and equipped with stopcocks that permit removal of air before the introduction of hydrogen. The mixed catalyst/solid substrate was placed at the bottom of the flask reactor to form a thin layer (2-3 mm) and then evacuated to approximately 10-3 Torr for 10 min. After introducing hydrogen (760 Torr), the reaction was carried out until complete transformation of the solid had occurred usually the reaction was completed within 18 h. This transformation was accompanied by the formation of thin needles on the surface of the solid catalytic bed, which correspond to the resulting products cA-4-tert-butylcyclohexanol, /ra s-4-/err-butylcyclohexanol and 4-tert-butylcyclohexanone. The reaction mixture was extracted with ethyl ether, and the catalyst separated by simple filtration. Analysis of the products was carried out by gas chromatography and mass spectroscopy. 

Within the cage, both fcrf-alkoxy and acryloxy radicals undergo side reactions. For example, tert-butoxy radicals d ompose to form acetone and methyl radicals while benzoyloxy radicals liberate carbon dioxide to form phenyl radicals. Fink [154] has studied the decomposition of benzoyl peroxide in benzene and analyzed the products using gas chromatography and mass spectroscopy. The three products produced were biphenyl (72%), phenyl cyclohexadiene (28%), and phenyl benzoate (0.3%). Using deuterated benzoyl peroxide, it was determined that these products arose from reaction with the benzene rather than radical combination within the cage. 

In general, remote gas-sensing methods cannot match the sensitivity of similar techniques deployed with long pathlength cells tmder laboratory conditions. Similarly, they cannot match the specificity of the best nonoptical techniques (e.g., gas chromatography or mass spectroscopy). 

The reduced and passivated catalysts were mixed with fine quartz powder (0.1-0.2 mm diameter) to insure isothermal operation and avoid bypassing, introduced into packed-bed reactors, and re-reduced in flowing H2 at 623-723 K for 2-4 h. After cooling to 473 K, the catalyst was exposed to H2 and CO reactants (H2/CO=2/l), temperatures were maintmed at 473 K and pressures at 2000 kPa. Data were collected after reaching steady state (24-36 hours), and the products were analyzed with gas chromatography and mass spectroscopy [S], Selectivities are reported as the percentage of reacted CO that appears as a ven product. 

Acrylonitrile in both biological and environmental samples is most commonly determined by gas chromatography with a nitrogen-phosphorus detector (GC/NPD) (Page 1985), gas chromatography/flame ionization detection (GC/FID) (EPA 1982a), or gas chromatography/mass spectroscopy (GC/MS) (Anderson and Harland 1980). Infrared spectroscopy (Jacobs and Syrjala... 

The conventional approach to solvent extraction is the batch method. Early work with this method was hampered by the low concentration of the compounds present and the relative insensitivity of the methods of characterization. Thus lipids and hydrocarbons have been separated from seawater by extraction with petroleum ether and ethyl acetate. The fractionation techniques include column and thin-layer chromatography with final characterisation by thin-layer chromatography, infrared, and ultra-violet spectroscopy and gas chromatography. Of these techniques, only gas chromatography is really useful at levels of organic matter present in seawater. With techniques available today such as glass capillary gas chromatography and mass spectrometry, much more information could be extracted from such samples [20]. 

Much less work has been focused on the effect of polymer structure on the resist performance in these systems. This paper will describe and evaluate the chemistry and resist performance of several systems based on three matrix polymers poly(4-t-butoxycarbonyloxy-a-methylstyrene) (TBMS) (12), poly(4-t-butoxycarbonyloxystyrene-sulfone) (TBSS) (13) and TBS (14) when used in conjunction with the dinitrobenzyl tosylate (Ts), triphenylsulfonium hexafluoroarsenate (As) and triphenylsulfonium triflate (Tf) acid generators. Gas chromatography coupled with mass spectroscopy (GC/MS) has been used to study the detailed chemical reactions of these systems in both solution and the solid-state. These results are used to understand the lithographic performance of several systems. 

Due to its relatively low sensitivity, the combination of gas chromatography with Fourier transform infrared spectroscopy (GC-FTIR) is not a standard technique in semiochemical research. Nevertheless, it could come in handy for the identification of some compounds with utterly uninformative mass spectra [22]. 

Isolation and identification of pyrazine alkaloids (Table III) have been achieved in most cases by a combination of gas chromatography and mass spectrometry (35,36,38,69,97,142). Methyl-, 2,3,6-trimethyl-, and tetramethylpyrazines (23a, 21a, and 22a) from the melon fly are identified by utilizing a solid sampling technique in conjunction with gas chromatography-mass spectroscopy (147). Methylpyrazines show the molecule ion as a base peak. Fragmentation proceeds mainly by the loss of HCN or CH3CN from the molecular ion (141). Eth-... 

The emission levels generated at the processing of HIPS were estimated from static monitors positioned around the engine. In the monitoring positions stainless steel tubes packed with Tenax and Chromosorb as a general purpose adsorbent material were established. After sampling, the adsorbed chemicals were desorbed at 250°C and subsequently analyzed by gas chromatography (GC) coupled with mass spectroscopy (MS). 

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