Solvent optimisation

The polarity index, P, is a numerical measure of the relative polarity of various solvents as determined from their solubility in some specific solvents. The polarity index for a mixture can then be readily determined from the polarity indices of the pure components and their respective volume fractions ( A, b), thus 

Any desired polarity index can be obtained by mixing the appropriate amounts of solvents. An increase in the polarity of the solvent mixture means a stronger eluant and hence smaller k values. This is expressed in the following relationship  

a two unit change in polarity index results in a 10-fold change in k. Often satisfactory resolution can be achieved by adjusting the capacity factor by modifying the solvent strength. If, however, separation is still 

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The enantioselective Michael reaction of malonates to nitroolefins catalysed by bifunctional amino-thioureas has recently been reported by Take-moto [161]. Excellent ee (75-93%) were obtained with diethylmalonate after solvent optimisation, toluene being the best solvent both for the activity and for the selectivity. Substituted malonates were then reacted with various nitroolefins under the same conditions. Excellent enantioselectivities were observed (Scheme 45). 

The first term is an elastic energy, for a molecule of extension L along the tube, with an unperturbed radius R0 given by Eq.(2). The second term describes monomer/monomer repulsions (in an athermal solvent). Optimising Eq.(14), we arrive at... 

A second example is the question of the polarity of ionic liquids, which has been addressed in various studies to-date. Chemists have developed a rather intuitive understanding of the nature of a solvent, which is often selected by rules-of-thumb such as similis similibus solvuntur (like dissolves like), and generalised categories such as protic/non-protic or polar/non-polar , which are used to choose a solvent. In general, the potential of solvent optimisation has probably not been fully exploited for any solvent system. 

The development of new chiral phases for preparative use is still an important topic even though more than a hundred phases are commercially available. The main features to be improved are selectivity, capacity and mechanical as well as chemical stability, especially against a wide variety of different solvents. Optimisation of the... 

When the chromatographic mode, column type, packing and dimensions have been chosen, the final stage of method development involves solvent optimisation and a choice between isocratic or gradient elution. Many separations can be achieved perfectly satisfactorily under isocratic conditions and are preferred to gradient elution techniques, as these are inconvenient due to the time required to re-equilibrate the column. A measure of the quality of separation is given by the resolution factor which can be expressed as follows ... 

Post-column on-line derivatisation is carried out in a special reactor situated between the column and detector. A feature of this technique is that the derivatisation reaction need not go to completion provided it can be made reproducible. The reaction, however, needs to be fairly rapid at moderate temperatures and there should be no detector response to any excess reagent present. Clearly an advantage of post-column derivatisation is that ideally the separation and detection processes can be optimised separately. A problem which may arise, however, is that the most suitable eluant for the chromatographic separation rarely provides an ideal reaction medium for derivatisation this is particularly true for electrochemical detectors which operate correctly only within a limited range of pH, ionic strength and aqueous solvent composition. 

Within the chemical industry, micro-organisms and enzymes are often used as catalysts. It is possible for a unit operation in an essentially chemical production process to be a biochemically catalysed step giving rise to a mixed chemical/biochemical production process. The products of these reactions include organic chemicals, solvents, polymers, pharmaceuticals, and purfumes. Mixed chemical/biochemical production processes are continuously innovated and optimised, mainly for economical reasons. 

Natural ingredients based lipstick formulations have been prepared. The effects of the natural waxes, oils and solvent compositions on the viscosity and melting point of the lipstick have been studied. The result indicates that the viscosity and melting point of the lipstick can be manipulated by changing the composition of natural candelilla wax, camauba wax and beeswax in the formulation. Another important lipstick characteristic, which is hardness, will be studied. Consumer acceptance towards the product will be investigated. Finally, by relating the consumer data and instrumentation analysis, optimisation process will be conducted. 

Various extraction methods for phenolic compounds in plant material have been published (Ayres and Loike, 1990 Arts and Hollman, 1998 Andreasen et ah, 2000 Fernandez et al., 2000). In this case phenolic compounds were an important part of the plant material and all the published methods were optimised to remove those analytes from the matrix. Our interest was to find the solvents to modily the taste, but not to extract the phenolic compounds of interest. In each test the technical treatment of the sample was similar. Extraction was carried out at room temperature (approximately 23 °C) for 30 minutes in a horizontal shaker with 200 rpm. Samples were weighed into extraction vials and solvent was added. The vials were closed with caps to minimise the evaporation of the extraction solvent. After 30 minutes the samples were filtered to separate the solvent from the solid. Filter papers were placed on aluminium foil and, after the solvent evaporahon, were removed. Extracted samples were dried at 100°C for 30 minutes to evaporate all the solvent traces. The solvents tested were chloroform, ethanol, diethylether, butanol, ethylacetate, heptane, n-hexane and cyclohexane and they were tested with different solvent/solid ratios. Methanol (MeOH) and acetonitrile (ACN) were not considered because of the high solubility of catechins and lignans to MeOH and ACN. The extracted phloem samples were tasted in the same way as the heated ones. Detailed results from each extraction experiment are presented in Table 14.2. 

For selection of alternative solvents (non-ozone depleting) for separation processes (extraction and HPLC mobile phase optimisation) references [24,25] are very useful. 

As may be seen from Table 3.22, MTBE does not extract additives from PA6, as opposed to dissolution in the expensive solvent HFIP. It is also evident that in these conditions intact Ultranox 626 is not observed the hydrolysis product 2,4-di-f-butylphenol (2,4-DTBP) is observed instead. 31P NMR confirms hydrolysis of Ultranox 626. The results do not discriminate between hydrolysis during mixing or analysis. As also SFE does not detect Ultranox 626 hydrolysis is likely to occur in the mixing step. Dissolution with HFIP and SFE (after optimisation) give identical results. In this case the added value of SFE extraction consists in a considerable cost reduction. 

Selection of a suitable extraction solvent is probably the most difficult step in optimising PFE for polymers [122]. Solvent selection used in PFE of any particular analyte can be done in several ways ... 

Two basic methods are used for SPME direct immersion of the fibre into the sample and headspace sampling. Experimental parameters comprise the polarity of the sample matrix and coating material, solvent and salting-out. Other parameters for optimisation of SPME conditions include desorption time, injector port temperature and initial oven temperature. 

In reality, finding a suitable solvent is not as easy as simply matching the polymer s solubility parameter (8 value). It is also important to take into account the effects of polymer crystallinity (as in the case of aPP and iPP, LDPE and HDPE). Because of their various chemical structures, it may be necessary to experiment with solvent, temperature, and time conditions to optimise the extraction strategy. 

While additive analysis of polyamides is usually carried out by dissolution in HFIP and hydrolysis in 6N HC1, polyphthalamides (PPAs) are quite insoluble in many solvents and very resistant to hydrolysis. The highly thermally stable PPAs can be adequately hydrolysed by means of high pressure microwave acid digestion (at 140-180 °C) in 10 mL Teflon vessels. This procedure allows simultaneous analysis of polymer composition and additives [643]. Also the polymer, oligomer and additive composition of polycarbonates can be examined after hydrolysis. However, it is necessary to optimise the reaction conditions in order to avoid degradation of bisphenol A. In the procedures for the analysis of dialkyltin stabilisers in PVC, described by Udris [644], in some instances the methods can be put on a quantitative basis, e.g. the GC determination of alcohols produced by hydrolysis of ester groups. 

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