Complex mixtures, laboratory studies

GC-IMS-MS instruments are ideally suited for laboratory studies, as a complex mixture can be separated ionisation in relatively clean systems can take place and the identity of the ions can be studied and verified by mass spectrometry [315]. However, the cost of such systems is quite prohibitive, and their complexity confines their utilisation to the laboratory. In GC-IMS-MS, the gas chromatograph is used to preseparate the components of the sample, with the IMS used as its detector. The ions that constitute the mobility spectrum are then further characterised by MS. 

While a majority of laboratory-scale dehydrocyclization studies involve carefully chosen feedstocks, often a single alkane, commercial operators use a naphtha fraction consisting of a complex mixture of hydrocarbons. At least some of these will be incapable of easily undergoing direct dehydrocyclization and need to be isomerized into reactive structures if aromatics are to be formed. The work of Davis suggests that the acidity of dual function catalysts is an important added factor in these isomerizations, one which likely complements the different set of isomerizations that may be catalyzed by the platinum function. 

Additional data are needed to better define the exposure of humans and, in the context of animal toxicity studies, of laboratory animals. Because JP-8 is a complex mixture of chemicals that differ in volatility, solubility, metabolic rate and pathway, and rate and route of elimination from the body, dosimetry of critical components of the mixture at critical sites in the body is important to enhance the quality of risk assessment. The fact that human exposures can involve liquid fuel, aerosolized fuel, and vapor, by inhalation, dermal, and oral routes of exposure makes it difficult to accurately predict the internal dose of JP-8 and its components. 

Recent advances in mass spectrometry have rendered it an attractive and versatile tool in industrial and academic research laboratories. As a part of this rapid growth, a considerable body of hterature has been devoted to the apph-cation of mass spectrometry in clinical studies. In concert with separation techniques such as hquid chromatography, mass spectrometry allows the rapid characterization and quantitative determination of a large array of molecules in complex mixtures. Herein, we present an overview of the above techniques accompanied with several examples of the use of liquid chromatography-tandem mass spectrometry in pharmacokinetics/drug metabohsm assessment during drug development. 

It was shown in the laboratory of P.T. Kaye that the reactions of 2-hydroxybenzaldehydes and 2-hydroxy-1-naphthaldehydes with various activated aikenes proceeded with regioseiective cyclization under Baylis-Hillman conditions to afford the corresponding 3-substituted 2H-chromene derivatives in high yields. Previous attempts to prepare 2H-chromenes chemoselectively via the cyclization of 2-hydroxybenzaldehyde-derived Baylis-Hillman products had proven unsuccessful. Complex mixtures containing coumarin and chromene derivatives were obtained. Good results were observed after the careful and systematic study of the various reactants and reaction conditions. 

The first step in the laboratory study of developmental toxicity is determination of the substance to be tested. This might be straightforward in drug or pesticide registration studies because only a single pure compound is of concern. In the case of complex mixtures, however, selection of the test substance(s) for the particular condition(s) and route(s) of exposure can be very difficult. For example, gasoline, diesel fuel, or aviation fuel each contain more than 250 diverse hydrocarbons, which change with source of the crude oil, the products are formulated differently... 

Foundry workers who are exposed to complex mixtures of gases and fine particles that include airborne particulates [H] and organic binders [L] have an elevated risk for lung cancer. In vitro laboratory studies have demonstrated mutagenic activity for these fumes, including free radical DNA damageJ53 ... 

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