GC-MS Studies

Clomiphene citrate is used as a mixture of E (58) and Z (60) isomers to treat infertility. Photolysis of a chloroform solution with a high-pressure mercury lamp gave the expected phenanthrenes (59) and (61), which were separated and identified by GC-MS. Study of the separate isomers (58) and (60) indicated that rapid cis-trans photoisomerization preceded ring closure so that each gave a mixture of phenanthrenes (60) and (61) (Scheme 2.2) [52],... 

The GC/MS study of methylated fulvic acid showed the presence of -hydroxybenzoic acid (ff 166), vanillic acid (Nr " 196), a methyldihydroxybenzoic acid (M " 210), coumaric acid (M+ 192), syringic acid (M" " 226), caffeic acid (fT " 222), ferulic acid (M" " 222), and stearic acid (M" " 298). The same compounds were present in humic acid, along with palmitic acid (M" " 270). The presence of these compounds was confirmed by TLC, using standard compounds. 

One of the major results of SEC-GC-MS studies is the discovery of an orderly pattern, by which various isomers and homologs of similar chemical species exist in coal liquids. For example almost any direct coal liquefaction process produces very similar species, which differ from each other by size and extent of isomerization but with an orderly distribution pattern. Alkanes... 

Birnessite (8-Mn02) Condensation of glucose and glycine (measurement of optical density) yields of humic substances XANES, Py-FIMS, and Curie-point Py-GC/MS studies of solid residue show that amide and heterocyclic N compounds are formed (dominant N forms in natural humic substances) Jokic et al. (2004a)... 

The SE-52 and SE-54 silica capillary columns used in the GC and GC/MS studies were purchased from J W Scientific, Inc. (Rancho Cordova, California). 

Optical measurements were carried out using a Technidyne S-4 Brightness Tester and Colorimeter. GC MS studies were preformed employing a HP 5890 Series IIGC and a HP 5971A Mass Selective Detector. 

Brown RS, Pettit K, Jones PW. 1989. A GC/GC-MS study of 2,3,7,8-TCDD using a DB-225 column and selected decomposition monitoring a quantitative tool. Chemosphere 19 171-176. 

Two other 8-oxo derivatives [coccoline (17) and coccolinine (15)] have been isolated from Cocculus species, and these are discussed separately later (see Section II,C,5). It has been recognized that, since oxidation at C-8 is relatively facile, the 8-oxo derivatives are probably artifacts produced in the drying process (55). Both 10,11-dehydroerysovine (34) and 10,11-dehydroerysodine (35), which have been detected in GC-MS studies, are thought to be artifacts produced by an elimination reaction from 11-methoxy-or 11-hydroxyalkaloids (12). 

In 1972, Sastry and Waller (59) reported the presence of dihydroajaconine during GC-MS studies of ajaconine isolated from D. ajacis. A sample of what had been earlier identified as pure ajaconine furnished a mixture of five compounds when the deuterated trimethylsilyl derivative was analyzed on the GC-MS. The temperature on the GC column (215°) and the time required for elution (12.7-27.8 min) may have given rise to rearrangement products. 

Y.-X. Li et al., Adsorption and decomposition of organophosphorus compounds on nanoscale metal oxide particles. In situ GC-MS studies of pulsed microreactions over magnesium oxide. Chem. Mater. 4, 323-330 (1992)... 

Since our group is no longer engaged in GC/MS studies on THC, only this single experiment has been conducted. Obviously it is risky to extrapolate from... 

To deduce the location of the double bond within the lipid backbone, the mixture (500 ng) was subjected to consecutive bisthiomethylation of the alkene85 and O-methyloxime formation (Equation 3). GC—MS study of the fragmentation of these derivatives (e.g., see 31, derived from 24) allowed simultaneous determination of the cleavage site (between C24 and C25) and of which portion contained the original ketone (i.e., the odd versus even mass fragments of 17 3 and 426 for 31). All of the monounsaturated lipid ketones had the alkene in the same downstream location in other words, they varied in the number of methylene units between the ketone and alkene functional groups but were constant in their -octyl terminal alkyl moiety. The four most major components (24, 25, 27, and 28) were prepared by chemical synthesis and used to confirm their identity in the natural pheromone and their pheromonal activity both alone and in admixtures. 

Ltndberg JJ, Ratsanen S, Niemt R (1982) GC-MS studies on the pyrolysis of wood and lignin Gov Rep Announce Index (US) 1984 84 163-173 Linskens HF, Jackson JF (1986) Gas chromatography/mass spectrometry Springer, Berlin Heidelberg New York Tokyo, 304 pp... 

Lindberg JJ, Raisancn S, Nicmi R (1982) GC-MS studies on the pyrolysis of wood and lignin. 

Extensive GC-MS studies of synthetic ceramide TMS derivatives [292,295,296] and free ceramides in plasma [297] have been made. They have also been identified in human aorta [298] and identified and quantitated in human platlets [299]. 

A Py-GC study [7] with pyrolysis done at 500° C showed numerous peaks corresponding to the isoprene dimers, trimers. .. up to hexamers eluting in clusters of peaks. The separation was done on a methyl silicone 5% phenyl silicone type column with FID detection. The results from a Py-GC/MS study [8] where natural rubber was pyrolysed at 580° C in a Curie point Py-GC/MS on-line system showed similar results. The TIC trace of the pyrolysate with the separation done on a 60 m Carbowax column, 0.32 mm i.d., 0.25 pm film thickness, with the temperature gradient of the GC oven between 40°... 

Some hemicelluloses have practical applications such as larch arabinogalactan, which is a water-soluble gum found in the heartwood of trees from Larix genus, and which is used in processed food as an emulsifier, or in pudding mixes, etc. A Py-GC/MS study of arabinogalactan from larch wood indicated the presence of the galactose unit and of arabinose unit in the ratio 6 1, as it is known in this material. The arabinose units were identified mainly by the formation of 1,4-anhydro-L-arabinopyranose, which elutes faster than the corresponding hexoses. The structure shown below was therefore confirmed by Py-GC/MS [64]. 

FI mass spectra were proven informative in algal polysaccharide analysis [2]. Characteristic Py-Fi mass spectra were reported for agarose, aiginic acid, laminaran, etc. Also, Py-GC/MS studies were done on algal polysaccharides [64a,64b]. The identification of pyrolysis products for several polysaccharides from red algae showed, as expected, compounds commonly obtained during polysaccharide pyrolysis. A list of several compounds found in these pyrolysates is shown in Table 7.8.2. 

The technique that seems to show best the fatty acid constituents is pyrolysis in the presence of a methylating agent (such as TMAH). Both Py-MS and Py-GC/MS studies were done using this procedure [5.14], This reaction seems to be a transesterification (with typical nucleophilic mechanism) where Ri is the long hydrocarbon chain of the fatty acid and R2 is the glycerol (or an alternative) residue. 

Besides structure elucidation for the browning polymer, Py-GC/MS studies were also done in connection with food related problems [10] such as the use of sugar-ammonia browning polymers as food colors. 

Several Py-MS and Py-GC/MS studies were performed on a variety of proteins. One common subject in these studies was determination of the amino acid composition of the protein. A number of studies were performed to determine the differences and similarities between proteins from a given class, such as hemoglobins of different origins or different enzymes, etc. [15-18]. 

By far, mass spectrometry (MS) is the most popular detection technique for performing chromatographic studies of essential oils. The use of retention indices, in conjunction with GC/MS studies, is well established. Many laboratories use such procedures in their routine analyses to confirm the identities of unknown components. The identification of components is usually performed by comparing the mass spectra with an MS library. However, a feature of MS for essential oils is that mass spectra are not particularly unique in many cases because of the large numbers of isomers of the same molecular formula, but with different structures, that could exist. Therefore their mass spectra are similar and... 

Compounds 6a, 7a, and 8a were isolated as viscous, colorless liquids. These compounds can be identified with NMR and GC-MS spectroscopy. In some cases unwanted and yield reducing side reactions like oligomerization or monoalkylation of the dichlorosilanes occur. Side products are not detected by NMR specroscopy, but GC-MS studies definitely show peaks at higher masses. In the H NMR spectra of 6a and 7a well-separated signals can be observed for the diastereotopic methylene protons at room temperature. Obviously the ring inversion process is slowed down if bulky substituents are used. 

On the other hand, GC/MS studies on the polycondensation of C2HsSiCl3 [11] suggest a two step mechanism, including rapid hydrolysis of the monomer and formation of linear, cyclic, and polycyclic products. The polyhedral silsesquioxanes are generated during a second and considerably slower step via cleavage and rebuilding from (strained) polysiloxane molecules. 

Other Py-GC and Py-GC/MS studies on polysiloxane copolymers are reported in literature [21, 22], etc. In one such study [21] several polysiloxanes used as liquid crystals, which contain benzyl ether and biphenyl ether side chain groups, were analyzed by Py-GC/MS. The general formula for these compounds is shown below ... 

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