Acetonitrile, methanol, and

Computed free energy surfaces of the triiodide ion in its ground state in acetonitrile, methanol, and aqueous solution are presented in Figure 4, in which the two I—I bond... 

As a final example of column durability and solvent resistance in small pore gels we were able to resolve nylon 6 oligomers using a methanol mobile phase and 205-nm UV detection as shown in Figure 13.29. In fact, polar solvents such as acetone, acetonitrile, methanol, and 2-propanol, are used routinely as needed with no ill effects. 

Dynamic light-scattering experiments or the analysis of some physicochemical properties have shown that finite amounts of formamide, A-methylformamide, AA-dimethyl-formamide, ethylene glycol, glycerol, acetonitrile, methanol, and 1,2 propanediol can be entrapped within the micellar core of AOT-reversed micelles [33-36], The encapsulation of formamide and A-methylformamide nanoclusters in AOT-reversed micelles involves a significant breakage of the H-bond network characterizing their structure in the pure state. Moreover, from solvation dynamics measurements it was deduced that the intramicellar formamide is nearly completely immobilized [34,35],... 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

Acetonitrile, methanol and DMSO had no apparent effect on umbelliferone glucuronidation in human hepatocytes at concentration up to 2% [32]. With HLMs or expressed UGTs, inhibitory effects of organic solvents on glucuronidation of 7-hydroxy-4-trifluoromethyl-coumarin (7-HFC) and estradiol generally followed the order acetonitrile > ethanol > methonal > DMSO [33], DMSO did not inhibit estradiol-3-glucuronidation activity at a concentration up... 

G.P. Cunningham, G.A. Vidulich, R.L. Kay, Several properties of acetonitrile-water, acetonitrile-methanol, and ethylene carbonate-water systems, Journal of Chemical and Engineering Data 1 (2) (1967) 336-337. 

Resolution can be mapped as a function of various proportions of acetonitrile, methanol, and THF in the mobile phase. Usually the k range or run time is held constant during the process by varying the amount of water in the mobile-phase mixture so as to compensate for small differences in the strength of the three pure organic solvents. If further improvement in separations is needed, the additives given in Table 15.8 should be considered. 

Three organic solvents, acetonitrile, methanol, and THF, are usually used as the organic modifiers. Increasing the concentration of the organic modifier decreases the overall retention times, but changes in relative retention times depend on the properties of the analytes. 

Figure 4.4 Polarity, proton acceptor and dipole properties of water and organic modifier mixtures.----------------, acetonitrile, --, methanol, and---tetrahydrofuran.

RP chromatography is the most applied technique to determine biotin in food samples. Instead, only some works report the use of HPLC as preparative chromatography [588]. Water, acetonitrile, methanol, and different bnffers are the most widespread mobile phases used. Recently, Holler et al. [589] have reported the nse of a hurt-cut HPLC system follow by MS detection to increase the sensitivity of the biotin response. 

RP chromatography is used for analytical determination of vitamin Bg, such as ODS, C18, and amide. The mobile phases used are, like for vitamin Bj and B2, acetonitrile, methanol, and water within a percentage of buffer. 

Calibration solutions were prepared by dissolving 60 mg of aspirin and 1.8 mg of salicylic acid in 50 ml of a solvent mix containing acetonitrile, methanol and orthophosphoric acid in the following concentrations 92 8 0.5 by volume respectively. 

Steps in method development (1) determine the goal of the analysis, (2) select a method of sample preparation, (3) choose a detector, and (4) use a systematic procedure to select solvent for isocratic or gradient elution. Aqueous acetonitrile, methanol, and tetrahydrofuran are customary solvents for reversed-phase separations. A separation can be optimized by varying several solvents or by using one solvent and temperature as the principal variables. If further resolution is required, flow rate can be decreased and you can use a longer column with smaller particle size. Criteria for a successful separation are 0.5 < < 20, resolution >2.0, operating... 

Solvent systems encompass a dizzying array of permutations of organic solvents, buffers, and other mobile-phase additives. However, the most commonly employed solvent systems involve acetonitrile, methanol, and/or tetrahydrofuran. Buffers are typically acetate (pKa 4.8) or phosphate (pKa 1.3 and 6.7) at approximately 100 mM. For the analysis of a small number of free amino acids, isocratic elution is often possible. For the determination of an overall amino acid profile from a hydrolysate sample, complicated ternary gradients are often necessary. 

Fig. 7 Typical reversed-pbase separation of amino acids. Precolumn derivatization of a standard amino acid mixture was achieved employing FMOC. Resolution was achieved by gradient elution with acetonitrile, methanol, and acetate buffer (pH 4.2) on a C,8 column. Standard three-letter abbreviations for amino acids are used also, CySO H = cysteic acid. (From Ref. 164. Copyright 1983 Elsevier Science.)...

Fig. 9 Chromatogram of the separation of the dabsyl derivatives of all 20 naturally occurring amino acids on a Cik column. Gradient elution employed acetonitrile, methanol, and acetate buffer (pH 6.5). Note the presence of a large peak due to the hydrolysis product of excess derivatizing reagent. Peaks marked with asterisks have not been identified. (From Ref. 154. Copyright 1991 Elsevier Science.)...

Several points had to be taken into consideration when choosing the mobile phase. First, the mobile phase had to dissolve the silver nitrate properly while at the same time being sufficiently nonpolar for the elution of saturated TGs. Second, the mobile phase had to be inert to silver ions so that no reaction would take place. Third, the refractive index of the mobile phase had to be different from that of the TGs, since TGs were to be detected using a refractive index detector. For these reasons, mobile phases such as propionitrile, acetonitrile, methanol, and 2-propanol were tested. The mobile phase that gave the best separation results was methanol-2-propanol (3 1 v/v) with dissolved silver nitrate. 

Values for other components in Table B.2 are given below. Except for acetic acid, acetonitrile, methanol and nitromethane, agreement is within... 

The quinoxalone derivatives of pyruvate and 2-ketobutyrate were separated on a /iBondapak Qg reversed-phase column (3.9 mm x 300 mm). The mobile phase was a mixture of acetonitrile, methanol, and 40 mM phosphate buffer (pH 7) (5 8 12, v/v/v) run at a flow rate of 1 mL/min. Detection could be carried out spectrophotometrically at 254 nm, or fluorometrically with excitation and emission wavelengths of 340 and 389 nm, respectively. 

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