Buffer ammonium oxalate/oxalic acid

In ammoniacal solutions of copper salts, the oxidation products are likely to contain nitrogen thus, hexoses give oxalic acid, imidazoles, hydrogen cyanide, and urea. Kinetic studies have been reported for the reaction of Cu(II) in the presence of ammonia with maltose, lactose, melibiose, and cellobiose.190 For the oxidation by tetraamminecopper(II) in ammoniacal and buffered media the rate of reaction is first order in disaccharide concentration, order one-half in ammonia concentration, but it is independent of Cu(II) concentration. The reaction rate is decreased by the addition of ammonium chloride, because of the common ion effect. These kinetics suggested mechanisms involving an intermediate enediolate ion, with the rate of reaction being equal to the rate of enolization.191 A similar mechanism has been proposed for the oxidation of D-fructose by a copper-pyridine complex in an excess of pyridine.192... 

Sample preparation Condition a Bond Elut C8 SPE cartridge with 5 mL MeOH and 5 mL water. 20 mL Milk + 1 mL 1 M oxalic acid, heat at 60° for 10 min, centrifuge for 10 min, remove the supernatant and add it to 20 mL water and 400 p-L triWtylamine, shake well, add to the SPE cartridge, wash with two 2.5 mL portions of water, elute with 2.5 mL MeOH. Evaporate the eluate to dryness under a stream of nitrogen, extract the residue with three 100 pL portions of 50 mM pH 6.0 potassium phosphate buffer, filter (0.2 pm), inject an aliquot of the filtrate. (Buffer w-.s 545 mL 100 mM citric add, 455 mL 200 mM Na2HP04, and 74.4 g EDTA, adjust to pH 4.5 with ammonium hydroxide, make up to 2 L with water.)... 

Acid ammonium oxalate, buffered to pH 3.3, has commonly been used to extract plant-available Mo from a soil. Its content in a majority of Indian soils has ranged between 0.10 and 0.8 tgg" . However, a few alluvial and... 

Pore fluids used in this study included distilled water, an acetate pH buffer, and 0.01 M oxalic acid with the acetate pH buffer. The buffer (4135 ppm total acetate) had an initial pH at 25 °C (pH,) of 4.7. The buffered oxalic acid (1000ppm oxalate, 4135 ppm acetate) had pHi = 4.2. Ammonium acetate/acetic acid (CH3COONH4/CH3COOH) was chosen as the pH buffer because acetic acid commonly occurs in formation waters in conjunction with difunctional carboxylic acids. The concentration of total acetate in the buffer was chosen to be in the range of that found in natural waters. In addition, the initial pH values (4.2-4.7) were chosen to be in the range of calculated values (4.0-5.5) for reservoir waters corrected for known amounts of degassing of CO2 and H2S (Kharaka et al. 1986). 

The effect of the hydration radius of these cations is very important, and mobilities are sometimes very close or the same as for potassium and ammonium. For this reason, a complexing agent is added to the buffer. Several complexing agents such as a-hydroxyiso-butyric acid (HIBA), 18-crown-6, phthalic, malonic, tartaric, lactic, citric, oxalic, or glycolic acid may be used. 

By subjecting extracts of rabbit muscle to a series of ammonium sulfate fractionations, a cut was obtained which had a turnover number of about 1400 per minute per 10 g. of protein. Since the enzyme is imusually labile to acid conditions in all purification procedures the pH had to be held above 7. There is evidence that the stability of the enzyme is affected not only by the pH but also by the nature of the ionic environment and concentration. Thus, certain anions such as oxalate, pyrophosphate, phosphate, and sulfate tend to stabilize buffered solutions of the enzyme. ... 

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