Programmed solvent characteristics

Solute property detectors, such as spectroscopic andj electrochemical detectors, respond to a physical or chemical] property characteristic of the solute which, ideally, is] independent of the mobile phase. Althou this criterion is rarely met in practice, the signal discrimination is usually sufficient to permit operation with solvent changes (e.g., flow programming, gradient elution, etc.) and to provide high sensitivity with aj wide linear response range. Table 5.4. Solute-specific detectors complement ulk property detectors as they provide high ... 

Gas chromatographic analysis starts with introduction of the sample on the column, with or without sample preparation steps. The choice of inlet system will be dictated primarily by the characteristics of the sample after any preparation steps outside the inlet. Clearly, sample preparation has a profound influence on the choice of injection technique. For example, analysts may skip the solvent evaporation step after extraction by eliminating solvent in the inlet with splitless transfer into the column. Sample introduction techniques are essentially of two types conventional and programmed temperature sample introduction. Vogt et al. [89] first described the latter in 1979. Injection of samples, which... 

As computers become more pervasive and increasingly powerful, specialized programs and databases are being developed to assist in a wide variety of research efforts. This is true in the search for solvent alternatives, and in this section we review the application of computers to solvent substitution studies and cover computer-aided molecular design of new solvents, methods developed for the prediction of physical properties, methods for predicting less precise chemical characteristics such as toxicity and carcinogenicity, and computer-aided design of alternative synthetic pathways. 

Solvent Selection. Solvent selection is often conducted in early design of chemical processes. A method to match desirable solvent properties (solubility parameters, for example) while simultaneously avoiding undesirable environmental impacts (persistence, toxicity, volatility, etc.) would improve design performance. PARIS II is a program combining such solvent design characteristics. Solvent composition is manipulated by a search algorithm aided by a library of routines with the latest fluid property prediction techniques, and by another... 

Mixed solvents prepared from two single solvents S, and S2 are attractive, because the properties of such mixtures may be varied in a programmed fashion by changing their composition. One should remember, however, that the change in such properties from those characteristic of S, to those typical of S2 is not always represented by a monotonic function since molecules of both solvents interact with one another and the solvation sphere of ionic reactants can be quite different from the bulk composition. 

Jandera, P. Churacek, J. Gradient elution in liquid chromatography II. Retention characteristics (retention volume, bandwidth, resolution, plate number) in solvent-programmed chromatography—Theoretical considerations. J. Chromatogr. 1974, 91, 223-235. 

Impact of solvent treatment of tobacco on cigarette burn characteristics and on mainstream smoke yields of selected compounds 59th Tobacco Science Research Conference, Program Booklet and Abstracts, Vol. 59, 4122. 

In GC capacity factors, retention and selectivity are controlled by adjusting the column temperature and stationary phase characteristics. In LC change in the composition of the eluant serves both purposes more effectively and thus solvent programming (otherwise known as gradient elution) is used in HPLC where temperature programming would be employed in GC. 

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