GLC-mass spectroscopy

The emphasis now being placed upon the GLC/mass spectroscopy combination is already paying a rich dividend in some areas of analytical chemistry. Further research on this combination is bound to lead to a quickening interest from instrument manufacturers. The need is for an apparatus which is sufficiently sensitive and which, in terms of expense and expert labor, is within the range of laboratories specializing in residue analysis. When a reasonably inexpensive and easy-to-use equipment, capable of working at trace concentrations, becomes available, it will have the capacity to solve many analytical problems. However, it will be some years before this kind of instrument is on the market. 

The products isolated by column chromatography on silica with hexane-ether as eluent were identified by and NMR and by GLC-mass spectroscopy. 

Procedures for etherification and esterification of carbohydrates for GLC analysis, advantages and disadvantages of the different methods of hydroxyl and aldehyde group derivatization, columns used for the separation of the various derivatives, detection methods for GLC, mass spectroscopy and fast atom bombardment (FAB) as well as outlines of some strategies for structural analysis of carbohydrates are described, discussed and reviewed in an excellent book on the analyses of carbohydrates by GLC (35). 

There are many references to the speciation of organotin compounds (particularly butyltin compounds) in marine sediments (see below), when compounds Uu Snk4 are separated by GLC or HPLC and analyzed by mass spectroscopy (MS),56 sometimes with isotope dilution.57-59... 

This method suffered from sensitivity problems initially as the bile-acid molecules lack a chromophore, but did offer the distinct advantage that conjugated bile acids could be determined without hydrolysis. The sensitivity issue was addressed by use of fluorescent derivatives such as dimethoxycoumarin esters with a C18 reverse phase column and were able to resolve endogenous mixtures of bile acids. The combination of hplc and mass-spectroscopy detection has further improved the sensitivity along with providing specific identification, important as the resolution of bile acids by hplc is not as good as capillary column glc. ... 

The reaction time was 3.5 hrs. The composition of the mixture of the reaction products determined by GLC was 65% ethylbenzene, 19.5% 3-phenylpropanal diethylacetal, and 10.5% ( —) (R)-2-phenylpropanal diethylacetal. The yield of hydroformylation products was 32%. The optically active acetal purified by preparative GLC (9) and identified by comparison of GLC and mass spectroscopy with a known sample had [< ]D25 —0.52° (neat). 

The main technique used is gas-liquid chromatography (abbreviated GLC or nowadays just GC), which is especially useful when combined with mass spectroscopy (MS) the combination is often referred to as GC-MS. They can provide both quantitative and qualitative information that is very accurate and reliable when compared to known analytical measurements of oils that are stored in databases. 

Thus, techniques used to give further evidence for the identity of a pesticide residue should be inteUigently chosen. If evidence from infrared or mass spectroscopy is not available, then adequate criteria of identification would be one or two GLC retention times, plus an Rp value from paper or thin-layer chromatography or an extraction p-value. Alternatively, one or two GLC retention times plus a GLC retention time of a derivative formed by chemical reaction would be a basis for confidence. 

Analysis of HPC products by the GLC method proved the presence of dimer, identified by the mass spectrometry technique. Dimer content dependence on time at various molar ratios of water/OTES was determined by GLC, silicon signal integral intensities in spectra of Si NMR, and mass spectroscopy (Fig. 2b). 

The essential apparatus for pressure measurement and analysis, and other important aspects such as furnaces and temperature control, are reviewed for thermal, photochemical and radiochemical systems. The latter two also involve sources of radiation, filters and actinometry or dosimetry. There are three main analytical techniques chemical, gas chromatographic and spectroscopic. Apart from the almost obsolete method of analysis by derivative formation, the first technique is also concerned with the use of traps to indicate the presence of free radicals and provide an effective measure of their concentration. Isotopes may be used for labelling and producing an isotope effect. Easily the most important analytical technique which has a wide application is gas chromatography (both GLC and Gsc). Intrinsic problems are those concerned with types of carrier gases, detectors, columns and temperature programming, whereas sampling methods have a direct role in gas-phase kinetic studies. Identification of reactants and products have to be confirmed usually by spectroscopic methods, mainly IR and mass spectroscopy. The latter two are also used for direct analysis as may trv, visible and ESR spectroscopy, nmr spectroscopy is confined to the study of solution reactions... 

Cave (1981) described the simultaneous detection of bioresmethrin and PBO by a GLC technique with chemical ionization mass spectroscopy on whole-grain wheat, Simonaitis (1983 extracted the residual PBO from bread prepared with com meal and wheat (lour. The extract was cleaned up and chromatographed on a column of Forex XXS (60-90 mesh). 

Thin-layer chromatography (TLC) was used to identify safrole, isosafrole, and dihydrosafrole in rat urine and bile (Fishbein et al., 1967). Gas chromatography-mass spectroscopy (GC-MS) and gas liquid chromatography-mass spectroscopy (GLC-MS) were utilized to identify the urinary metabolites of safrole in the rat (Klungsoyr and Scheline, 1983). Plasma and tissue safrole concentrations in rats and humans were measured by GC-MS. Urinary metabolites were identified using TLC and GC-MS (Benedetti et al., 1977). 

In 1979 Bickley and Vishwanathan reported that N2 was oxidized in a series of experiments in which Ti02 was irradiated under air or a nitrogen oxygen mixture of unspecified composition. A similar effect was observed when Ti02 was irradiated under pure oxygen and subsequently exposed to N2. Products were thermally desorbed and analyzed by mass spectroscopy in conjunction with GLC [122], The putative catalyst was 99% pure commercially available rutile powder with water adsorbed on its surface prior to irradiation. The surface area of the powder was determined by krypton absorption at 78 K to be 13m2g 1. The experimental apparatus was not described. 

Products were analyzed by GLC on diisodecyl phthalate columns operated at 25°C. for 10 minutes, and programmed at 10°C./min. thereafter. Effluent fractions were trapped at 77 °K. and characterized further by ultraviolet, infrared, and mass spectroscopy. Quantitative analyses of B and DB, after the radiolysis of DB, were based on calibrations with synthetic mixtures. Polymer yields (solids of molecular weight comparable to or greater than that of perfluorobiphenyl) were determined as previously described (11). 19F NMR spectra were run in CC1 solution with CCI3F as internal reference. 

Major plant sterols. The major sterols identified in tomato seed oil are p-sitosterol (54-71%), stigmasterol (10-17%), campesterol (4.2-5.8%), brassicasterol (1.3-3%), 7-stigmastenol (trace-1.4%) and cholesterol (7-27%) (Tiscornia et al., 1976). Tiscomia et al. (1976) have examined the cholesterol in ten cultivars and found it to vary with cultivar. With careful evaluation as TMS derivatives, using two different GLC columns and mass spectroscopy, they claim that it is authentic cholesterol. They propose a possible pathway for production in higher plants. Santos (1982) has reported an average of 12.8% cholesterol in tomato seed oil and similar values for the other sterols. Mannino and Amelotti (1975) likewise report about 16% cholesterol in tomato seed oil. 

A large number of new unsymmetric tetraorganogermanes are recently reported in the literature. The field has benefited from better synthetic methods for preparation of intermediate halides and introduction of modern analytical techniques. Especially useful have been nuclear magnetic resonance (NMR) and mass spectroscopy combined with gas liquid phase chromatography (GLC), the latter both on analytical and preparative scale. 

Prop. GLC (1939) Anal. detn. in n-Bu Sn from Grignard rxn. by mass spectroscopy and chromatographic method (2838). 

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