Nonaqueous buffer

Buffer Nonaqueous Basic—Add 10 mL of buffer stock Solution B to 100 mL of titration solvent. Use within 1 h. 

Tetiafluoioethylene—peifluoiopiopyl vinyl ethei copolymeis [26655-00-5] aie made in aqueous (1,2) oi nonaqueous media (3). In aqueous copolymerizations water-soluble initiators and a perfluorinated emulsifying agent are used. Molecular weight and molecular weight distribution are controlled by a chain-transfer agent. Sometimes a second phase is added to the reaction medium to improve the distribution of the vinyl ether in the poljmier (11) a buffer is also added. 

The activity of the hydrogen ion is affected by the properties of the solvent in which it is measured. Scales of pH only apply to the medium, ie, the solvent or mixed solvents, eg, water—alcohol, for which the scales are developed. The comparison of the pH values of a buffer in aqueous solution to one in a nonaqueous solvent has neither direct quantitative nor thermodynamic significance. Consequently, operational pH scales must be developed for the individual solvent systems. In certain cases, correlation to the aqueous pH scale can be made, but in others, pH values are used only as relative indicators of the hydrogen-ion activity. 

A more difficult criterion to meet with flow markers is that the polymer samples not contain interferents that coelute with or very near the flow marker and either affect its retention time or the ability of the analyst to reproducibly identify the retention time of the peak. Water is a ubiquitous problem in nonaqueous GPC and, when using a refractive index detector, it can cause a variable magnitude, negative area peak that may coelute with certain choices of totally permeated flow markers. This variable area negative peak may alter the apparent position of the flow marker when the flow rate has actually been invariant, thereby causing the user to falsely adjust data to compensate for the flow error. Similar problems can occur with the elution of positive peaks that are not exactly identical in elution to the totally permeated flow marker. Species that often contribute to these problems are residual monomer, reactants, surfactants, by-products, or buffers from the synthesis of the polymer. 

Aqueous GPC can also be semiprepped in manner just like nonaqueous GPC. In this case one must consider carefully the buffers, salts, and biocides used in the eluant. If the fractions are destined for nuclear magnetic resonance experiments it will be imperative to either reduce the salt concentration in the eluant or remove salt after the initial fractionation. Likewise, if the collected samples are destined for infrared (IR) analysis, it is important to choose salts and buffers that have good IR transparency in the wavenumber ranges of interest. 

As reported by Griengl and coworkers, benzaldehyde, decanal, undecanal, and dodecanal were reacted with HCN in a two-phase solvent system aqueous buffer and ionic liquids 1 -ethyl-3-methylimidazolium tetrafluoroborate, 1 -methyl-3-propylimidazolium tetrafluoroborate, and l-butyl-3-methyl-imidazolium tetrafluoroborate in the presence of the HNLs from Prunus amygdalus and Hevea brasiliensis. When compared with the use of organic solvents as the nonaqueous phase, the reaction rate was significantly increased and the enantioselectivity remained good [51]. 

Dissolve the amine-containing PAM AM dendrimer in methanol or a buffered aqueous medium at a pH of 7-9 (e.g., 50mM sodium phosphate, pH 7.5) and at a concentration of at least lOmg/ml. Note that Singh (1998) used a concentration of llOmg/ml in methanol, but other dendrimer concentrations should work equally well. For nonaqueous reactions, the addition of a proton acceptor may aid in driving the reaction to maximal yields (i.e., triethylamine or dimethylaminopyridine). 

The NHS ester end of NHS-LC-biotin reacts with amine groups in proteins and other molecules to form stable amide bond derivatives (Figure 11.4). Optimal reaction conditions are at a pH of 7-9, but the higher the pH the greater will be the hydrolysis rate of the ester. Avoid amine-containing buffers which will compete in the acylation reaction. NHS-LC-biotin is insoluble in aqueous reaction conditions and must be solubilized in organic solvent prior to the addition of a small quantity to a buffered reaction. Preparation of concentrated stock solutions may be done in DMF or DMSO. Nonaqueous reactions also may be done with this reagent for the modification of molecules insoluble in water. The molar ratio of NHS-LC-biotin to a... 

The authors reasoned that the aqueous succinic anhydride capping buffer (comprised of 96% NMP and 4% sodium borate) may have led to the redissolving of probe DNA fhaf was subsequently randomly redeposited over the entire slide, leading to elevated backgrormd. As a result, a reformulation of succinic anhydride info a nonaqueous medium of dichloroet-hane (DCE) solvenf confaining N-methylimidazol (acylation catalyst) was undertaken. Significant improvements in interspot backgrounds were evident. 

Various processes separate rare earths from other metal salts. These processes also separate rare earths into specific subgroups. The methods are based on fractional precipitation, selective extraction by nonaqueous solvents, or selective ion exchange. Separation of individual rare earths is the most important step in recovery. Separation may be achieved by ion exchange and solvent extraction techniques. Also, ytterbium may be separated from a mixture of heavy rare earths by reduction with sodium amalgam. In this method, a buffered acidic solution of trivalent heavy rare earths is treated with molten sodium mercury alloy. Ybs+ is reduced and dissolved in the molten alloy. The alloy is treated with hydrochloric acid, after which ytterbium is extracted into the solution. The metal is precipitated as oxalate from solution. 

The electrochemistry of oxo-bridged manganese complexes in aqueous solution is characterized by coupled electron and proton-transfer reactions. The cyclic voltammetric behavior of [Mn2 02(phen)4] + in aqueous pH 4.5 phosphate buffer is illustrated in Fig. 12 [97]. It is of interest to compare this result with that obtained for the same complex dissolved in CH3CN (Fig. 9). Two one-electron reactions are observed in each case. However, these correspond to Mn(IV,IV) Mn(IV,III) and Mn(IV,III) Mn(III,III) reductions in the nonaqueous solvent and to Mn(IV,III) Mn(III,III) and Mn(III,III) Mn(III,II) reductions in... 

The effectiveness of the coating has been investigated by separating phenolic compounds in the nonaqueous media. The EOF was found to be anodic and dependent on the pH of the separation buffer. In anofher study [66], imidazole containing zwitterionic salt (N-3-(-triethoxysilylpropyl)-4,5-dihy-droimidazole) was attached to the silica capillary wall via the formation of a covalent bond (Figure 6.8). 

Perhaps the best-known method of preparing aromatic azo compounds involves the coupling of diazonium salts with sufficiently reactive aromatic compounds such as phenols, aromatic amines, phenyl ethers, the related naphthalene compounds, and even sufficiently reactive aromatic hydrocarbons. Generally, the coupling must be carried out in media which are neutral or slightly basic or which are buffered in the appropriate pH range. The reaction may also be carried out in nonaqueous media. While some primary and secondary aromatic amines initially form an A-azoamine, which may rearrange to the more usual amino-C-azo compound, tertiary amines couple in a normal manner. 

Under some conditions, phenolic ethers are dealkylated during coupling. However, the dealkylation follows the coupling step and is acid-catalyzed. Consequently, use of an excess of sodium acetate as a buffer or use of a nonaqueous medium obviates the dealkylation. 

Lyophilized enzymes have a pH memory, meaning that the activity of the enzyme in organic solvent parallels its pH-activity profile of the aqueous solution from which it was lyophilized [36, 79-81]. However, very often acidic or basic mixtures within a nonaqueous reaction mixture such as reactant, products, or impurities, can disrupt this delicate protonation state, leading to changes in catalytic activity. To counteract this potential problem, solid-state buffers have been developed to protect the enzyme s protonation state in the nonaqueous environment [53, 82]. These solid-state buffers contain pairs of crystalline solids that can be intercon-... 

Semiaqueous or Nonaqueous Solutions. Although the measurement of pH in mixed solvents (e.g., water/organic solvent) is not recommended, for a solution containing more than 5% water, the classical definition of a pH measurement may still apply. In nonaqueous solution, only relative pH values can be obtained. Measurements taken in nonaqueous or partly aqueous solutions require the electrode to be frequently rehydrated (i.e soaked in water or an acidic buffer). Between measurements and after use with a nonaqueous solvent (which is immiscible with water), the electrode should first be rinsed with a solvent, which is miscible with water as well as the analyte solvent, then rinsed with water. Another potential problem with this type of medium is the risk of precipitation of the KC1 electrolyte in the junction between the reference electrode and the measuring solution. To minimize this problem, the reference electrolyte and the sample solution should be matched for mobility and solubility. For example, LiCl in ethanol or LiCl in acetic acid are often used as the reference electrode electrolyte for nonaqueous measurements. 

With TSP, ammonium acetate has emerged as the best general-purpose electrolyte for ionizing neutral samples. Improved ionization can be obtained by the use of a filament or discharge electrode to generate reactive ions for CI (87, 88). The processes involved in filament or discharge-assisted ionization must be used when operating in the absence of a buffer with nonaqueous eluents. With ionic analytes, the mechanism of ion evaporation is supposed to be primarily operative since ions are produced spontaneously from the mobile phase (89). Ion evaporation often yields mass spectra with little structural information in order to overcome this problem, other ionization modes or tandem MS have been applied (90). 

An aqueous medium, either water or a buffered solution preferably not exceeding pH 6.8, is recommended as the initial medium for development of an IVIVC. Sufficient data should be submitted to justify pH greater than 6.8. For poorly soluble drugs, addition of surfactant (e.g., 1% sodium lauryl sulfate) may be appropriate. In general, nonaqueous and hydroalcoholic systems are discouraged unless all attempts with aqueous media are unsuccessful. Appropriate review staff in CDER should be consulted before using any other media. 

Total ionic strengths of solutions in the cells were varied from about 0.005M to ca. 0.02Af. The concentrations of solutions in cell C were made so that the buffer ratio in Equation 15 always had a value between 0.4 and 0.6. The nonaqueous cosolvents used in this study were Reagent Grade or better, and they were tested to be sure that they were free from significant quantities of potentially interfering substances such as halide ions, acids, and bases. Densities of tetra-hydrofuran-water mixtures were determined pycnometrically at 15° C and at 35°C. 

Dissolve the entire sample. If the sample is not soluble in dilute aqueous buffer, try adding 6 M urea or surfactants. Acetate buffer tends to dissolve more organic solutes than does phosphate buffer. If necessary, nonaqueous solvents can be used.53... 

Pushing detection limits of nitroaromatic explosives into the parts per trillion (ppt) level requires sample preconcentration. Collins and coworkers used solid-phase extraction (SPE) of explosives from sea water which was followed by rapid on-chip separation and detection [18]. Explosives were eluted from SPE column by acetonitrile and were injected in the microchip separation channel. Lab-on-a-chip analysis was carried out in nonaqueous medium. The mixed acetonitrile/methanol separation buffer was used to produce the ionized red-colored products of TNT, TNB and tetryl [27,28]. The chemical reaction of the bases (hydroxide and methoxide anions) with trinitroaromatic explosives resulted in negatively charged products, which were readily separated by microchip... 

Capillary electrophoresis separation is performed in a flexible fused silica capillary tube that is filled with an appropriate buffer solution of defined pH and ionic strength (aqueous/nonaqueous). A small volume of sample (lower than 3-4% of the column volume) is needed to achieve efficient separation. This volume is introduced hydrodynamically (or less often electrokinetically) into the capillary to which an electrical potential is applied (Figure 13.7). Charged species of the sample exhibit... 

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