Arsenite, determination

The methods in which iodine is used as a catalyst for the reaction between ceric sulfate and nitrite or arsenite (86,87) are capable of determining smaH amounts of iodine. However, these catalytic methods are deHcate and require accurate timing, carefiH temperature control, and special apparatus. 

Methylene iodide [75-11-6], CH2I2, also known as diio dome thane, mol wt 267.87, 94.76% I, mp 6.0°C, and bp 181°C, is a very heavy colorless Hquid. It has a density of 3.325 g/mL at 20°C and a refractive index of 1.7538 at 4°C. It darkens in contact with air, moisture, and light. Its solubiHty in water is 1.42 g/100 g H2O at 20°C it is soluble in alcohol, chloroform, ben2ene, and ether. Methylene iodide is prepared by reaction of sodium arsenite and iodoform with sodium hydroxide reaction of iodine, sodium ethoxide, and hydroiodic acid on iodoform the oxidation of iodoacetic acid with potassium persulfate and by reaction of potassium iodide and methylene chloride (124,125). Diiodoform is used for determining the density and refractive index of minerals. It is also used as a starting material in the manufacture of x-ray contrast media and other synthetic pharmaceuticals (qv). 

The hberated iodine, as the complex triiodide ion, may be titrated with standard thiosulfate solution. A general iodometric assay method for organic peroxides has been pubUshed (253). Some peroxyesters may be determined by ferric ion-catalyzed iodometric analysis or by cupric ion catalysis. The latter has become an ASTM Standard procedure (254). Other reducing agents are ferrous, titanous, chromous, staimous, and arsenite ions triphenylphosphine diphenyl sulfide and triphenjiarsine (255,256). 

A widely used procedure for determining trace amounts of tellurium involves separating tellurium in (1 1) hydrochloric acid solution by reduction to elemental tellurium using arsenic as a carrier and hypophosphorous acid as reductant. The arsenic, reduced from an addition of arsenite to the solution, acts as a carrier for the tellurium. The precipitated tellurium, together with the carrier, is collected by filtration and the filter examined directly in the wavelength-dispersive x-ray fluorescence spectrometer. 

It is well known that arsenic is one of the most dangerous elements in terms of its potential impacts to both to human and ecosystem health. Therefore the problem of As detection at ppb level remains very important from the point of environmental hazard investigation. The goal of the present work is the developing of very simple and inexpensive assay for arsenite and arsenate determination in environmental samples using whole-cell bacterial biosensors. 

The developed assay was successfully applied for the arsenite and arsenate determination in contaminated waters of the gold recovery plant and in snow covers of the industrial anthropogenic sources vicinities as well. The data produced are in a good agreement with the results of independent methods atomic absorptioin and atomic emission spectrometry and capillary electrophoresis. 

Arsenites may also be determined by this procedure but must first be oxidised by treatment with nitric acid. Small amounts of antimony and tin do not interfere, but chromates, phosphates, molybdates, tungstates, and vanadates, which precipitate as the silver salts, should be absent. An excessive amount of ammonium salts has a solvent action on the silver arsenate. 

In the determination of formic acid in more complicated reaction-mixtures (for example, in the presence of buffers,22 69a in solutions containing non-volatile acids,49- 67 and in solutions containing ammonia234), it was necessary to distil the formic acid from the reaction solution (after destruction of the excess periodate with ethylene glycol or arsenite) before it could be titrated. 

Haywood and Riley [14] have described a spectrophotometric method for the determination of arsenic in seawater. Adsorption colloid flotation has been employed to separate phosphate and arsenate from seawater [15]. These two anions, in 500 ml filtered seawater, are brought to the surface in less than 5 min, by use of ferric hydroxide (added as 0.1 M FeC 2 ml) as collector, at pH 4, in the presence of sodium dodecyl sulfate [added as 0.05% ethanolic solution (4 ml)] and a stream of nitrogen (15 ml/minutes). The foam is then removed and phosphate and arsenate are determined spectrophotometrically [16]. Recoveries of arsenate and arsenite exceeding 90% were obtained by this procedure. 

Johnson and Pilson [229] have described a spectrophotometric molybdenum blue method for the determination of phosphate, arsenate, and arsenite in estuary water and sea water. A reducing reagent is used to lower the oxidation state of any arsenic present to +3, which eliminates any absorbance caused by molybdoarsenate, since arsenite will not form the molybdenum complex. This results in an absorbance value for phosphate only. 

Reinke, J., J.F. Uthe, H.C. Freeman, and J.R. Johnston. 1975. The determination of arsenite and arsenate ions in fish and shellfish by selective extraction and polarography. Environ. Lett. 8 371-380. 

In coastal environment, detrital and authigenic Fe and Mn oxides, which accumulate in oxic surface sediments, play a pivotal role in determining the geochemical behaviour of arsenic (Mucci et al., 2000) and selenium (Belzile et al., 2000). Arsenic and selenium differ in their affinities for metal oxide surfaces. Although both adsorb onto iron oxides, arsenate (As(V)) adsorbs more strongly than arsenite (As(lll)), and selenite (Se(IV)) adsorbs more strongly than selenate (Se(VI)) (Belzile et al., 2000). 

A typical breakthrough curve was observed for the column filled with Zr-loaded activated carbon after about 8000 pore volumes. This correspond to a uptake of 2.8 mg As/g. The concentrations in the outlet of the column with Absorptionsmittel 3 increased after about 4000 pore volumes, but no typical breakthrough curve was observed. The uptake until this point was only 2 mg As/g that is much lower than it was determined in the batch experiments. An explanation for this early increasing of the concentrations may be the high flow rate in comparison of the slow kinetics. The best results gave the column filled with the granular iron hydroxide. No breakthrough was observed up to now (12,000 pore volumes) and an uptake of about 2 mg As/g could be measured. The arsenite concentrations in the outlet of all three columns were very low and indicate an oxidation reaction. 

Dobolyi and Bidlo [76] have described methods for the determination of phosphorus in lake sediments. Shulka et al. [75] investigated the interference by arsenic in the perchloric acid digestion procedure of Murphy and Riley [85] for the determination of phosphorus in sediments. Arsenite concentrations up to 20pg did not interfere but arsenate interfered. Between 1 and 45 pg arsenic g"1 was extracted from a lake sediment and in all cases the error in the determination of phosphorus due to the presence of arsenic was less than 1%. 

Kit solution for the determination of toxic anions (e.g., arsenate, arsenite, azide, or cyanide) and other inorganic and organic anions with indirect UV detection... 

Iodine has the ability to catalyze many redox processes that are otherwise kinetically extremely slow. The detection and determination of As(III) in the form of arsenite is an important problem in the context of drinking water supply. The direct electrochemical As(III)/As(V) oxidation at various types of electrodes is not possible. However, in the presence of electrogenerated iodine, the As(III)/As(V) oxidation... 

Cardo PP, Lombardo C, Gatti R (1985) A simple detection of sialic acid storage disorders by urinary free and total sialic acid determinations. Clin Chim Acta 150 129-135 Denny PC, Denny PA, Allerton SE (1983) Determination of sialic acid using 2-thiobarbituric acid in the absence of hazardous sodium arsenite. Clin Chim Acta 131 333-336... 

Spike recovery and detection limit. Species of arsenic found in drinking water include AsO (arsenite), AsO - (arsenate), (CH3)2As02 (dimethylarsinate), and (CH3)AsO (methylarsonate). Pure water containing no arsenic was spiked with 0.40 pg arsen-ate/L. Seven replicate determinations gave 0.39, 0.40, 0.38, 0.41, 0.36, 0.35, and 0.39 pg/L.12 Find the mean percent recovery of the spike and the concentration detection limit (pg/L). 

To estimate arsenite and arsenate when present together, the former may first be determined in a portion of the solution by titration with iodine in the presence of sodium bicarbonate. Another portion is acidified strongly with hydrochloric acid, some ferrous sulphate and potassium bromide are added and the whole of the arsenic is distilled off as chloride and collected in water.2 The reduction may also be accomplished by cuprous chloride.3 The arsenious acid in the aqueous distillate is determined as above and the arsenic acid found by difference. 

Some of the volumetric methods described above may also be adapted to the electrometric determination of arsenic. Such methods have been described for titration of arsenites with ceric sulphate,9 iodine in the presence of sodium bicarbonate,10 chloramine (p-toluene-sulphone chloramide),11 alkaline potassium ferricyanide solution,12 potassium bromate13 or potassium iodate14 in the presence of hydrochloric acid, silver nitrate15 (by applying a secondary titration with 01N alkali to maintain the desired low H+-ion concentration), and with... 

The uses of constant-current coulometry for the determination of drugs in biological fluids are few, basically due to sensitivity restriction. Monforte and Purdy [46] have reported an assay for two allylic barbituric acid derivatives, sodium seconal and sodium sandoptal, with electrogenerated bromine as the titrant and biamperometry for endpoint detection. Quantitative bromination required an excess of bromine hence back titration with standard arsenite was performed. The assay required the formation of a protein-free filtrate of serum with tungstic acid, extraction into chloroform, and sample cleanup by back extraction, followed by coulometric titration with electrogenerated bromine. The protein precipitation step resulted in losses of compound due to coprecipitation. The recoveries of sodium seconal and sodium sandoptal carried through the serum assay were approximately 81 and 88%, respectively. Samples in the concentration range 7.5-50 pg/mL serum were analyzed by this procedure. 

Analysis When it is known that a chlorite is the only active oxidg agent present, it is easily determined by titration of the iodine liberated from KI in an acidified soln. A chlorite does not liberate iodine until the soln is acidified this serves as a qualitative distinction from a hypochlorite. The quantitative analysis of a soln contg chlorite 8c hypochlorite requires detn of the total oxidg power. Hypochlorite is detd on a separate sample by addg an excess of Na arsenite, after making certain the soln is alk. This "soln is saturated with... 

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