Buffer, aqueous

In 1965, the Dubna workers found a longer-lived lawrencium isotope, 256Lr, with a half-life of 35 s. In 1968, Thiorso and associates at Berkeley used a few atoms of this isotope to study the oxidation behavior of lawrencium. Using solvent extraction techniques and working very rapidly, they extracted lawrencium ions from a buffered aqueous solution into an organic solvent — completing each extraction in about 30 s. 

In reverse-phase chromatography, which is the more commonly encountered form of HPLC, the stationary phase is nonpolar and the mobile phase is polar. The most common nonpolar stationary phases use an organochlorosilane for which the R group is an -octyl (Cg) or -octyldecyl (Cig) hydrocarbon chain. Most reverse-phase separations are carried out using a buffered aqueous solution as a polar mobile phase. Because the silica substrate is subject to hydrolysis in basic solutions, the pH of the mobile phase must be less than 7.5. 

This experiment focuses on developing an HPLG separation capable of distinguishing acetylsalicylic acid, paracetamol, salicylamide, caffeine, and phenacetin. A Gjg column and UV detection are used to obtain chromatograms. Solvent parameters used to optimize the separation include the pH of the buffered aqueous mobile phase, the %v/v methanol added to the aqueous mobile phase, and the use of tetrabutylammonium phosphate as an ion-pairing reagent. 

From the data in Fig. 4.8b, estimate the shift factors required to displace the data at 0 = 0.5 (consider only this point) so that all runs superimpose on the experiment conducted at 128 C at 0 = 0.5. Either a ruler or proportional dividers can be used to measure displacements. Criticize or defend the following proposition Whether a buffered aqueous solution of H2O2 and 1. containing small amounts of S2O3 and starch, appears blue or colorless depends on both the time and the temperature. This standard general chemistry experiment could be used to demonstrate the equivalency of time and temperature. The pertinent reactions for the iodine clock are... 

The bimodal profile observed at low catalyst concentration has been explained by a combination of two light generating reactive intermediates in equihbrium with a third dark reaction intermediate which serves as a way station or delay in the chemiexcitation processes. Possible candidates for the three intermediates include those shown as "pooled intermediates". At high catalyst concentration or in imidazole-buffered aqueous-based solvent, the series of intermediates rapidly attain equihbrium and behave kineticaHy as a single kinetic entity, ie, as pooled intermediates (71). Under these latter conditions, the time—intensity profile (Fig. 2) displays the single maximum as a biexponential rise and fall of the intensity which is readily modeled as a typical irreversible, consecutive, unimolecular process ... 

Tripotassium dicitratobismuthate [57644-54-9] (bismuth subcitrate), De-Nol is a buffered aqueous suspension of a poorly defined, water-insoluble bismuth compound. It is said to very effective for the treatment of gastric and duodenal ulcers (180,184). There have not yet been any reports of bismuth encephalopathy following the use of this dmg. 

Dutch State Mines (Stamicarbon). Vapor-phase, catalytic hydrogenation of phenol to cyclohexanone over palladium on alumina, Hcensed by Stamicarbon, the engineering subsidiary of DSM, gives a 95% yield at high conversion plus an additional 3% by dehydrogenation of coproduct cyclohexanol over a copper catalyst. Cyclohexane oxidation, an alternative route to cyclohexanone, is used in the United States and in Asia by DSM. A cyclohexane vapor-cloud explosion occurred in 1975 at a co-owned DSM plant in Flixborough, UK (12) the plant was rebuilt but later closed. In addition to the conventional Raschig process for hydroxylamine, DSM has developed a hydroxylamine phosphate—oxime (HPO) process for cyclohexanone oxime no by-product ammonium sulfate is produced. Catalytic ammonia oxidation is followed by absorption of NO in a buffered aqueous phosphoric acid... 

Fig. 8.P21. pH-Rate profile for hydrolysis of A in buffered aqueous solution at 70 C.

The eoneentration of ozone in O2/O3 mixtures ean be determined by eatalytie deeomposition to O2 in the gas phase and measurement of the expansion in volume. More eonveniently it ean be determined iodometrieally by passing the gas mixture into an alkaline borie-aeid-buffered aqueous solution of KI and determining the I2 so formed by titration with sodium thiosulfate in aeidified solution ... 

Attempts to isolate 1,4-dihydroquinoxalinc itself were not successful, but the polarographic behavior of quinoxaline and 6-substituted quin-oxalines in buffered aqueous media suggests that in all cases reduction stops at the 1,4-dihydro stage/ - 2,3-Dimethylquinoxaline and 2-d-araho-tetrahydroxybutylquinoxaline show similar polarographic be-havior, ... 

Pont trademark -2KHS05-KHS04-K-,S04 with buffered aqueous acetone. 

Hydrolysis of substrates is performed in water, buffered aqueous solutions or biphasic mixtures of water and an organic solvent. Hydrolases tolerate low levels of polar organic solvents such as DMSO, DMF, and acetone in aqueous media. These cosolvents help to dissolve hydrophobic substrates. Although most hydrolases require soluble substrates, lipases display weak activity on soluble compounds in aqueous solutions. Their activity markedly increases when the substrate reaches the critical micellar concentration where it forms a second phase. This interfacial activation at the lipid-water interface has been explained by the presence of a... 

C18-0143. Virtuaiiy aii investigations in cell biology and biochemistry must be carried out in buffered aqueous... 

The cathodic approach has been investigated actively as a method for the production of thin film CdS, in particular for the fabrication of heterojunction cells. Photoactive CdS films could be grown in alkaline NH3/NH4Cl-buffered aqueous solutions containing thiosulfate as sulfur source and complexed Cd (EDTA+NH3), on Ti substrates [41]. The electroreduction of thiosulfate was considered to proceed as... 

Studies performed on CdS [282, 283] have revealed the importance of the microstructure, i.e., crystal structure, crystallite size, and geometrical surface area, in both the control of band structure and the concentration and mobility of charges, in relation to the photocatalytic performance of the photocatalyst. It has been shown also that the solubility product of CdS colloids prepared from acetate buffer aqueous solutions of suitable precursors increases from 7.2x 10 for large particles to about 10 for small (< 2.5 nm) particle colloids, this increase invoking a positive shift on the cathodic corrosion potential [284]. 

Swanson MB, WA Ivancic, AM Saxena, JD Allton, GKO Brian, T Suzuki, H Nishizawa, M Nokata (1995) Direct photolysis of fenpyroximate in a buffered aqueous solution. J Agric Food Chem 43 513-518. 

T. P. Lockhart and G. Burrafato. Gellable buffered aqueous composition and its use in enhanced petroleum recovery. Patent EP 390281, 1990. 

Figure 17.14 Cyclic voltammograms recorded at 1 V s at a PGE RDE rotating at 2500 rev min ) modified by adsorption of a submonolayer film of [NiEe]-hydrogenase from the purple photosynthetic sulfur bacterium Allochromatium vinosum in buffered aqueous solution at pH 7.0 under an atmosphere of H2 (1 bar). Reprinted with permission from Leger et al., 2002. Copyright (2002) American Chemical Society.

Figure 17.16 Electrocatalytic H2 oxidation by Ralstonia metallidurans CH34 membrane-bound hydrogenase on a PGE RDE in the presence of O2. The eiectrode is rotated at 2000 revmin and poiarized at +0.142 V vs, SHE in buffered aqueous solution at pH 5.6 and 30 °C, close to 1 bar H2. Reprinted with permission from Vincent et al. [2007]. Copyright (2007) American Chemical Society.

In situations involving acidic/basic analytes, pH is often the most critical property in the extraction, and buffered aqueous solvents are often necessary. Another important consideration is the stability of the analytes in the extraction medium, and method development should entail analyte stability experiments to demonstrate how long solutions and/or extracts can be stored. 

Sn/V/Nb/Sb/0 catalysts were prepared with the co-precipitahon technique, developed for the synthesis of ratile Sn02-based systems claimed by Rhodia (8). The preparation involved the dissoluhon of SnCl45H20, VO(acac)2, SbCh and NbCls in absolute ethanol, and by dropping the soluhon into a buffered aqueous soluhon maintained at pH 7. The precipitate obtained was separated from the liquid by filtrahon. The solid was then dried at 120°C and calcined in air at 700°C for 3 hours. The V/Sb/0 catalyst was prepared by means of the slurry method that consists in a redox reachon between Sb203 and NH4VO3 in water medium, for 18h at 95°C. The... 

Epoxidation by Dioxirane Derivatives. Another useful epoxidizing agent is dimethyldioxirane (DMDO),86 which is generated by in situ reaction of acetone and peroxymonosulfate in buffered aqueous solution. Distillation gives about aO.lM solution of DMDO in acetone.87... 

Hexafluoroacetone and hydrogen peroxide in buffered aqueous solution can epoxidize alkenes and allylic alcohols.101 N, Af-Dialkylpiperidin-4-one salts are also good catalysts for epoxidation.102 The polar effect of the quaternary nitrogen enhances the... 

Aliphatic and aromatic primary amines are rapidly and efficiently oxidized to nitro compounds by dimethyldioxirane.111 Dimethyldioxirane is prepared by reaction of OXONE (DuPont trademark)-2KHS05-KHS04-K2S04 with buffered aqueous acetone.112... 

Absorption ultraviolet-visible (UV-Vis) and fluorescence emission spectra of the aromatic pyrido[l,2-A]pyridazinium cation were measured in buffered aqueous solutions <2002MI37>. 

An HPLC method was developed that confirmed the photodegradation of [14C] niclosamide in sterile, pH 5, 7, and 9 buffered aqueous solutions under artificial sunlight at 25.0 1.0°C [70]. These degradates were carbon dioxide and two- and four-carbon aliphatic acids formed by cleavage of both aromatic rings. 

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). 

Fluorescein-5-thiosemicarbazide is soluble in DMF or in buffered aqueous solutions at pH values above 7.0. The reagent may be dissolved in DMF as a concentrated stock solution before adding a small aliquot to an aqueous reaction medium. The compound itself and all solutions made with it should be protected from light to avoid decomposition of its fluorescent properties. 

---