Effect of solvent strength

The most commonly used solvents for RPLC are methanol, acetonitrile, and tetrahydrofuran, used in binary, ternary, or quaternary combinations with water. The effect of solvent strengths can be seen in... 

Fig. 3.128. Effect of solvent strength on the chromatograms of a standard solution prepared by dissolving /1-CD ([/1-CD] = 9.5 mM) and the commercially available dediazoniation products 4-nitrophenol ([PNBOH] = 2.00X104 M), nitrobenzene ([NBH] = 1.98X10-4 M and 4-chloro-nitrobenhenzene ([PNBC1] = 1.99X10 4 M). (a) Mobile phase MeOH-water (75 25, v/v), (b) ACN-water (75 25, v/v). Reprinted with permission from C. Bravo-Diaz et al. [177].

FIGURE 5-28. Effect of solvent strength upon retention with constant pH and ionic strength. The compounds are chlorpheniramine (2) and propranolol (3). The mobile phase is acetonitrile/water with 4 M dibasic ammonium phosphate at pH of 7.8. The column is silica. (Reprinted with reference 4 with permission.)... 

Effect of Solvent Strength on Retention Factors. Solvents that interact strongly with. solutes are often termed strong" solvents. Strong solvents are often, but not always, polar solvents. Solvent strength depends on the nature of the analyte and stationary phase. Several indexes have been developed fur quantitatively describing the polarity of solvents. The most useful of these for partition chromatography is the polarity index P which was developed by Snyder." This parameter is based on. solubility measurements for the substance in question in three solvents dioxane (a low ... 

Following completion of the initial experiment, the focus shifts to the separation of the test mixture or organic compounds using the HPLC instrument. The effect of solvent strength on k and the effect of mobile-phase flow rate on will be considered by retrieving previously developed Turbochrom methods and making manual injections. 

Kiridena, W. Poole C. F. Koziol, W. W. The Effect of Solvent Strength and Temperature on Retention for a Polar-Endcapped, Octadecylsiloxane-bonded Silica Stationary Phase with Methanol-Water Mobile Phases. 

Gokhale, A., Khusid, B., Dave, R. N., Pfeffer, R. (2007). Effect of solvent strength and operating pressure on the formation of submicrometer polymer particles in supercritical microjets. The Journal of Supercritical Fluids, 43, 341-356. 

Several workers have attempted to use the common ion technique to depress [Pn+] and thus to achieve a monoeidic Pn+A system, as was done so successfully for anionic systems. However, because generally the solvents used for cationic polymerisations are much more polar, the KD of the chain-carriers and of the common-ion salts are considerably greater than in the anionic systems. Therefore the electro-chemical situation is likely to be complicated by triple ion formation and the effects of ionic strength on the KD and on the rate-constants, so that any results obtained by extrapolations to infinite ionic strength need to be scrutinised most carefully. 

W Williams, GT Young. Amino acids and peptides. XXXV. Effect of solvent on the rates of racemization and coupling of acylamino acid p-nitrophenyl esters. Base strengths of amines in organic solvents, and related investigations. J Chem Soc Perkin Trans 1 1194, 1972. 

The effect of a change in solvent on the secondary a-deuterium KIEs 195 Secondary a-deuterium KIEs and the effect of ionic strength on transition state structure 197... 

The Hg(II) assisted aquation of Co(III)-chloro complexes has been throughly studied to gain insight into the effects of solvent, ionic strength and polyelectrolytes on reaction rates and equilibria. For the two reactions in 1.0 M HCIO4 (4.39) and (4.40), (N)j representing five nitrogen donors in unidentates or multidentates or mixtures thereof. 

Recall from transition state theory that the rate of a reaction depends on kg (the catalytic rate constant at infinite dilution in the given solvent), the activity of the reactants, and the activity of the activated complex. If one or more of the reactants is a charged species, then the activity coefficient of any ion can be expressed in terms of the Debye-Htickel theory. The latter treats the behavior of dilute solutions of ions in terms of electrical charge, the distance of closest approach of another ion, ionic strength, absolute temperature, as well as other constants that are characteristic of each solvent. If any other factor alters the effect of ionic strength on reaction rates, then one must look beyond Debye-Hiickel theory for an appropriate treatment. 

Effect of solvent on El vs. E2 vs. ElcB. With any reaction a more polar environment enhances the rate of mechanisms that involve ionic intermediates. For neutral leaving groups, it is expected that El and ElcB mechanisms will be aided by increasing polarity of solvent and by increasing ionic strength. With certain substrates, polar aprotic solvents promote elimination with weak bases (the E2C reaction). 

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