Sodium arsenate buffer

Sodium Arsenate Buffer (To Make 1 Litre) Sodium arsenate (Na2HAs04.7H20 31.2 g) is dissolved in 800 ml water then 0.2 M EDTA (10 ml) and then magnesium sulfate (MgS04.7H20 2.46 g dissolved in 100 ml water) are added and the pH is adjusted to 7.4. The final volume is then adjusted to 1,000 ml. This provides a solution 0.1 M with respect arsenate, 0.01 M with respect to Mg2+, and 0.02 M with respect to EDTA. 

L-Amino acid oxidase has been used to measure L-phenylalanine and involves the addition of a sodium arsenate-borate buffer, which promotes the conversion of the oxidation product, phenylpyruvic acid, to its enol form, which then forms a borate complex having an absorption maximum at 308 nm. Tyrosine and tryptophan react similarly but their enol-borate complexes have different absorption maxima at 330 and 350 nm respectively. Thus by taking absorbance readings at these wavelengths the specificity of the assay is improved. The assay for L-alanine may also be made almost completely specific by converting the L-pyruvate formed in the oxidation reaction to L-lactate by the addition of lactate dehydrogenase (EC 1.1.1.27) and monitoring the oxidation of NADH at 340 nm. 

Inorganic As(III) and As(V) were determined by atomic absorption spectrometry using the hydride technique. Total inorganic arsenic, As(III) + As(V), was measured after a prereduction reaction of As(V) to As(III) in acidic solution containing potassium iodide and ascorbic acid. For the selective hydride formation of As(III), samples were maintained at pH 5.0 during the hydride reaction (with 3% NaBH4, 1% NaOH) with a citrate-sodium hydroxide buffer solution (31). As(V) was determined by difference between total As and As(III). The detection limit of As(III) and As(V) was 0.1 nM. The selectivity of this method was checked by additions of As(III) and As(V) to lake water 95-100% recovery of As(III) and As(V) was found (32). 

Figure 3. Reciprocal of the rate (M/min) of glycerophosphate dehydrogenase-catalyzed reduction of dihydroxyacetone in the presence of 5 mM arsenate vs the reciprocal of enzyme concentration (mg/mL). Reactions were carried out in Tris buffer (20 mM, pH 8.0) containing NADH (0.1 mM), dihydroxyacetone (50 mM), glycerophosphate dehydrogenase and sodium arsenate (5 mM). The decrease in absorbance at 340 nm was monitored versus time.

Anion-exchange chromatography with a 30 mM sodium phosphate buffer solution at pH 6 was used for the separation of arsenous acid, DMA, MA, and arsenic acid on the polymer-based Hamilton PRP-XlOO anion-exchange column... 

Experiments with house flies pointed to a considerable buffering action in the intestine.3 Solutions of arsenious acid and of the stoichiometric quantities of sodium hydroxide and arsenious oxide to form normal sodium arsenite, containing 15 g. of sucrose per 100 c.c., were fed to adult flies. The pH values of the former solutions were 6-58 to 6-96 and of the latter 11-3 to 11-4, but the toxicities were equal, being 0-14 mg. As per g. body weight—a large value for an insect. None of these solutions was repellent to the flies, but if the pH was increased beyond 11-4 repellent action was observed house fly bait therefore should not contain more alkali than is necessary to hold the arsenic in solution. The eradication of the tsetse fly by similar means is difficult. There is not much chance of a poisonous dose being taken from the skin of a dipped animal, but a toxic dose can be taken up from an arsenic-impregnated area by means of the proboscis.4... 

Calculate the masses of cacodylic acid and sodium ca-codylate that should be used to prepare 500.0 mL of a buffer at pH = 6.60 that has a total concentration of all arsenic-containing species equal to 0.25 M that is,... 

Sodium phosphate provides excellent buffering for fixatives at 0.1 M and is often used in place of cacodylate. Each buffer system has certain advantages and limitations. Cacodylate is an organic arsenic compound, dimethylarsenate, which is poisonous. Whereas it may provide additional TEM contrast in biological samples, it is a relatively weak buffer at pH 7.2. Alternatively, phosphate requires fewer safety precautions. However, our laboratory has observed precipitants in some biological samples, such as avian erythrocytes, that were attributed to the phosphate buffer. 

Tin ions are reduced to tin hydride from a boric-acid-buffered medium by means of sodium borohydride, transferred to a heated quartz cuvette by a current of inert gas, decomposed thermally, and the absorption of the atoms is measured in the beam of an atomic-absorption spectrometer. In the hydride technique, the element which is to be determined is volatilized as a gaseous hydride and in this way separated off from the matrix. Interference may occur if there is a considerable excess of elements such as antimony, arsenic, bismuth, mercury, selenium or tellurium which can also be volatilized with this technique. Above all, heavy metals such as copper and nickel in the solution have a disturbing effect during hydride formation itself. Interference due to phosphoric acid and hydrochloric acid may also be observed. It is therefore vital to check the method by the addition technique. 

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