Acetonitrile-methanol solvent

Residues of isoxaflutole, RPA 202248 and RPA 203328 are extracted from surface water or groundwater on to an RP-102 resin solid-phase extraction (SPE) cartridge, then eluted with an acetonitrile-methanol solvent mixture. Residues are determined by liquid chromatography/tandem mass spectrometry (LC/MS/MS) on a Cg column. Quantitation of results is based on a comparison of the ratio of analyte response to isotopically labeled internal standard response versus analyte response to internal standard response for calibration standards. 

Preparation 2-6 First, 2.5 g (0.01 mol) of 5-(2,4-difluorophenyl)salicylic acid, 0.21 g (0.005 mol) of lithium hydroxide monohydrate, and 0.31 g (0.005 mol) of boric acid were put into a flask, and an acetonitrile/methanol (2 1 by volume) solvent was added thereto, preparing a mixed solution. The mixed solution was refluxed for 8 h and agitated at room temperature for one night. Next, the solution was concentrated down to 1/4 thereof and allowed to stand at room temperature, obtaining a white crystal. The white crystal was filtrated and recrystallized using an acetonitrile/methanol solvent. Then, the recrystallized product was dried in a 100°C vacuum oven for 24 h, obtaining lithium bis[5-(2,4-difluorophenyl)salicylato-2-]borate. 

Hydrolysis of TEOS in various solvents is such that for a particular system increases directiy with the concentration of H" or H O" in acidic media and with the concentration of OH in basic media. The dominant factor in controlling the hydrolysis rate is pH (21). However, the nature of the acid plays an important role, so that a small addition of HCl induces a 1500-fold increase in whereas acetic acid has Httie effect. Hydrolysis is also temperature-dependent. The reaction rate increases 10-fold when the temperature is varied from 20 to 45°C. Nmr experiments show that varies in different solvents as foUows acetonitrile > methanol > dimethylformamide > dioxane > formamide, where the k in acetonitrile is about 20 times larger than the k in formamide. The nature of the alkoxy groups on the siHcon atom also influences the rate constant. The longer and the bulkier the alkoxide group, the lower the (3). 

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. 

This thinking has carried through to the present day and is reflected in our choices of mobile-phase fluids in LC water, acetonitrile, methanol, tetrahydrofuran, hexane, etc., are still among our popular choices. However, these particular materials are completely dependent on the conditions of column temperature and outlet pressure. Tswett s original conditions at his column outlet, actually the earth-bound defaults we call ambient temperature and pressure, determined his solvent choices and continue to dominate our thinking today. 

Figs. 1.6 and 1.7). This type of CD spectrum is observed for certain heterooligomeric peptoid sequences with as few as 33% chiral aromatic residues, in both aqueous and polar organic solvent (acetonitrile, methanol). 

Classical extraction is achieved by mixing the samples with an organic solvent (solid-liquid extraction) such as acetonitrile, methanol, or ethanol, used either in the pure form or as a mixture or aqueous solution." Extraction time can be reduced by sonicating the samples. ... 

OS 38] [reactor and protocol given in [107]] By reaction of N,N-dimethylaniline with 4-nitrobenzenediazonium tetrafluoroborate, the corresponding azobenzene derivative is obtained at a conversion of 37% using methanol (protic solvent) or acetonitrile (aprotic solvent) under electroosmotic flow conditions [107] (see also [14]). 

The highest yield of 14% was foimd at 2.5 fluorine-to-toluene equivalents (58% conversion 24% selectivity) [13]. This yield was obtained using acetonitrile as solvent slightly lower yields were obtained for methanol (Figiue 5.16). The selectivities were as high as for acetonitrile, the conversion being lower. Still lower yields (7%)... 

GL 1] [R 4] [P 2] Variation of solvent affects also the substitution pattern to a certain extent [13], A ratio of ortho-, meta- and para-isomers for mono-fluorinated toluene amounting on average to 3.5 1 2 was found in the dual-channel micro reactor at room temperature, using acetonitrile as solvent [13]. Using methanol as solvent, the ratio was on average 5.5 1 2.4. Hence more products referring to an electrophilic substitution were formed [13]. 

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... 

Tsuji and Goetz24 developed a quantitative high performance liquid chromatographic method for separating and measuring erythromycins A, B, and C, their epimers and degradation products. This method uses a /iBondapak Ci 8 reverse column with acetonitrile-methanol-O.2m ammonium acetate-water (45 10 10 25) as solvent. The pH and composition of the mobile phase may be adjusted to optimize resolution and elution volume. The authors utilized the procedure on USP reference standard and report a relative standard deviation of 0.64%. 

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. 

Benzobarrelenes are an important class of molecule where the di-jr-mcthanc rearrangement is operative. Clearly, within this class there is a possibility that benzo-vinyl interactions can be in competition with vinyl-vinyl processes. The direct irradiation (X > 330 nm) of the benzobarrelene 313 in a variety of solvents (benzene, acetonitrile, methanol or hexane) affords two principal products 314 and 315 in a ratio of 1 1. The products are formed via a di-7r-methane process involving vinyl-vinyl bridging which... 

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. 

Five organic solvents [acetonitrile, methanol, tetrahydrofuran (THF), acetone, and dimethylformamide], which are homogeneously miscible with water, have been used as modifiers to study the relationship of the selectivity of the solvent to the molecular properties of analytes. The polar interaction... 

Organic solvents (e.g., acetonitrile, methanol, etc.) help solubilize some hydrophobic proteins, and they can affect the Stokes radius, interaction with counterions, and the ionization state of the polypeptide. For more hydrophobic samples, the use of detergents and/or other organic solvents may prove beneficial. 

Alkanes are functionalised by anodic oxidation in acetonitrile, methanol, acetic acid and more acidic solvents such as trifluoracetic acid and fluorosulphuric acid. Reaction requires very positive electrode potentials (see Table 2.1) and platinum has generally been used as anode materials in laboratory scale experiments. On a larger scale carbon is used as anode material. The first stage in these reactions in-... 

In gradient elution of weak acids or bases, gradients of organic solvent (acetonitrile, methanol, or tetrahydrofuran) in buffered aqueous-organic mobile phases are most frequently used. The solvent affects the retention in similar way as in RPC of nonionic compounds, except for some influence on the dissociation constants, but Equations 5.8 and 5.9 usually are accurate enough for calculations of gradient retention volumes and bandwidths, respectively. 

C18 column from different suppliers (3-5 pm of particle size) are commonly used for amino acid determination, with mobile phases consisting of an acetate or phosphate buffer and an organic solvent such as acetonitrile, methanol, or tetrahydrofuran. To avoid peak tailing for the basic amino acids (in the presence of uncapped silanols), triethylamine is often added as a modifier. Depending on the complexity of the sample, complicated tertiary gradients can be necessary to separate all the researched amino acids [196],... 

Both NP (428, 441, 442) and RP (427, 436, 437) chromatography has been applied to analysis of vitamin A and provitamin A. A Lichrosorb Si60 column (250 mm x 4.6 mm) has been used for NP chromatography using hexane and hexane/2-propanol as mobile phase [441], More widespread are C8, C18, and C30 column with acetonitrile, methanol, water, and mixtures of these as the most used mobile phase [424,427,428,443], Chavez-Servm et al. [442] reported the use of a short narrow-bore column (50 mm X 2 mm id), which enables less solvent consumption and higher mass sensitivity. 

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. 

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