Critical comparison of two standard digestion procedures for the determination of total mercury in natural water samples by cold vapour atomic absorption spectrometry

Two pretreatment procedures for total mercury determinations in natural water samples were compared. The first, the Swedish Standard method (DP1), involves digestion of water in the presence of concentrated nitric acid at 120°C and under pressure for 30 min. In the West German Standard method (DP2), small volumes of nitric and sulphuric acids, permanganate and peroxodisulphate are added to the sample, and digestion proceeded at 50°C in an ultrasonic bath. Mercury was determined after both digestion procedures using a modified cold vapour atomic absorption spectrometric method, in which mercury generated on addition of a reducing agent is collected and subsequently atomized in a platinum-lined graphite furnace. The efficacy of the two digestion procedures was tested using various standard organic mercury compounds and it was found that only DP2 provided quantitative recoveries. Purification of the reagents required by DP2 was achieved using a mercury-selective ion-exchange resin, Chelite S, resulting in blank levels below 1.5 ng Hg l^?1. Both methods were applied to the determination of total mercury in an unpolluted marsh water sample, giving 2.0 ng Hg l^?1 (DP1) and 2.7 ng Hg l^?1 (DP2). The West German Standard digestion procedure (DP2) is recommended for the determination of total mercury in natural water samples.     

Spectrophotometric determination of calcium in zirconium powder by use of murexide

An accurate spectrophotometric method is proposed for the determination of calcium in zirconium powder by use of murexide. A 0.4-g sample is dissolved in hydrofluoric and sulphuric acids, the solution evaporated to fumes of sulphuric acid, and a mercury cathode electrolysis made if more than 0.05% copper or nickel is present. Ammoniacal precipitation in the presence of ammonium chloride separates zirconium and other elements and an aliquot of filtrate is collected, equivalent to 0.2 g of sample. The ammonium salts are destroyed with nitric and hydrochloric acids and the calcium is determined with murexide. The high reagent blank is shown to be due to the reagent grade nitric acid, hydrochloric acid, and ammonium hydroxide.     

Simultaneous determination of mercury and selenium in biological materials by radiochemical neutron activation analysis

A simple and sensitive radiochemical neutron activation analysis (RNAA) method has been developed for the simultaneous determination of mercury and selenium in biological materials. The radiochemical procedure is based upon the digestion of irradiated samples with sulphuric and nitric acids followed by subsequent extractions of mercury and selenium into toluene, first of mercury from 7.5 M H₂SO₄-0.01M HBr media and after of selenium from 7M H₂SO₄-1 M HBr media. After washing of the organic phases with similar media, the mercury bromide was back-extracted into 0.034M EDTA in 5% aqueous ammonia and the selenium bromide into 0.14M H₂O₂ in aqueous solution. The¹⁹⁷Hg and the⁷⁵Se were counted on a Ge(Li) detector. The precision and accuracy of the method was checked by analysing NBS Standard Reference Materials: orchard leaves and bovine liver.     

A modified catalytic-photometric method for the determination of vanadium in chloride rich hydro-geochemical samples

The vanadium content in chloride rich hydrogeochemical samples has been determined through a modification in the existing standard gallic acid oxidation method which has severe interference problem from halides. The modification incorporates a preliminary fume-drying of the sample aliquot with a mixture of perchloric and sulphuric acids. This ensures total removal of halides and hence their interference. The estimation is completed as per the standard method after taking the sample in 10 ml of 1% nitric acid. Also mercuric nitrate addition which forms a part of the standard procedure to prevent halide interference, is also dispensed with keeping in view the toxic nature of mercury. The method has been tried on a number of samples having varying chloride content. The results obtained compare well with the standard PAR method. The method can be used to determine vanadium down to 1 ppb. The relative standard deviation obtained for vanadium contents in the range 400–10 ppb is in the range 4–8.2%.     

Determination of chloride by displacement of hydrogen cyanide from mercury(II) cyanide

A method, based on the passivity of mercury(II) cyanide in dilute sulphuric acid and its reaction with hydrochloric acid to produce hydrogen cyanide, has been developed for the determination of small amounts of chloride. Hydrogen cyanide, distilled from a mercury(II) cyanide-halide-dilute sulphuric acid system is found by iodometric measurement to be directly proportional to the amount of chloride or bromide and of hydrogen ion in acids such as sulphuric acid. A linear correlation also holds for iodide but the stoichiometry is different, the titration values being about three times larger than expected. By conversion of the cyanide into a dye by means of the pyridine-pyrazolone reagent, 0.014-0.43 mug ml chloride concentrations have been determined. The method is also applicable to bromide and sulphuric acid in small amounts but not to fluoride and iodide. Results are reproducible to within +/-2%.     

A new routine method for determination of iodine in plant materials

A new method is suggested for determination of iodine in grass and crop samples. The sample is decomposed with sulphuric, nitric and perchloric acids. Iodine is determined in the diluted digest. The method is excellent for routine work, being faster and simpler than previous nethods.     

The determination of silver in sulphide minerals by atomic absorption spectrophotometry

Silver can be determined in sulphide minerals by atomic absorption spectrophotometry after decomposition with nitric and/or sulphuric acid with addition of tartaric acid to prevent precipitation of antimonic acid. The amount of silver retained in the residue is negligible if the acids used are completely chloride-free or if mercury(II) nitrate is added.     

Determination of phosphorus in phosphazenes and phosphines

An improved technique for the determination of phosphorus in organic phosphazenes and phosphines is described. An acid digestion using a mixture of fuming nitric, sulphuric and perchloric acids converts the organically bound phosphorus into orthophosphate. The orthophosphate is precipitated as magnesium ammonium phosphate, which is ignited to magnesium pyrophosphate. With this technique phosphorus was determined in several compounds. The results establish both good accuracy and precision for the method.     

Collection of mercury from artificial sea-water with activated carbon

Nanogram amounts of mercury(II) and methylmercury in artificial sea-water containing mineral acids as preserving reagents were shown to be collected quantitatively with activated carbon. Mercury concentrated on activated carbon was determined directly by combustion, trapping on gold and electrothermal atomic-absorption spectrophotometry. The activated carbon was purified by heating at 350 degrees for 2 hr. Sulphuric acid and hydrochloric acid were purified by treatment with activated carbon. Interference from iodide was eliminated by using a carbonate buffer wash before the atomic-absorption measurement. Less than 4 ng of mercury in 200-300 ml of artificial sea-water, whether acidified or not (with sulphuric, hydrochloric or nitric acid), was satisfactorily collected with 100 mg of activated carbon. Mercury was also collected quantitatively after oxidative treatment of artificial sea-water.     

A comparison of two digestion procedures for the determination of selenium in biological material

Two digestion procedures have been tested on samples of flour, blood and urine for application in the determination of selenium by hydride-generation atomic-absorption spectrometry. The first utilizes a mixture of concentrated nitric, perchloric and sulphuric acids and the second a mixture of magnesium nitrate hexahydrate, concentrated nitric acid and 6M hydrochloric acid. The accuracy of the procedures was tested by analysis of standard reference materials and by comparison with results from neutron-activation analysis. It was found that the "magnesium method" can replace the more common procedure, which includes perchloric acid, for the sample types investigated in this paper.     

Suitability of nitric-sulphuric acid decomposition for the determination of tungsten and molybdenum in geochemical exploration

A mixture of nitric and sulphuric acids is used for the decomposition of geochemical samples for the estimation of tungsten. In the resulting sample solution tungsten is determined colorimetrically by the dithiol method. The decomposition procedure suggested works well for scheelite mineral. However wolframite is only partially decomposed. The same sample solution is used for estimation of molybdenum by the thiocyanate method. The method is suitable for batch analysis and results in a high throughput.     

Submicro determination of cobalt, manganese or nickel in organometallic compounds

Methods for the determination of cobalt, manganese or nickel in samples of organometallic compounds weighing 30-100 mug have been developed. Spectrophotometric determination following digestion with nitric and sulphuric acids in a sealed tube is recommended, all results obtained from the analysis of standard compounds being within +/-0.4% absolute error. Digestion in an open tube with perchloric and sulphuric acids gives slightly low results for cobalt and nickel compounds and is inappropriate for manganese compounds.     

The determination of cadmium,lead and copper in urine by differential pulse anodic stripping voltammetry

Differential pulse anodic stripping voltammetry is used for the simultaneous determination of cadmium, lead and copper in different types of urine samples. Unlike most biological samples, urine can be analyzed directly for cadmium and lead without pretreatment of the sample; a significant increase in sensitivity is obtained if the analysis is carried out at an elevated temperature. The complete decomposition of urine with a mixture of nitric, perchloric and sulphuric acids is also described; this procedure makes it possible to determine copper simultaneously. Good agreement was obtained between the two procedures, and the recovery of metals from spiked samples was satisfactory for both methods. The relative merits of the two approaches are discussed.     

Submicro determination of aluminium, bismuth and copper in organometallic compounds

Methods for the determination of aluminium, bismuth or copper m samples of organometallic compounds weighing 40-110 microg have been developed. Spectrophotometric determination following digestion with nitric and sulphuric acids in a sealed tube is recommended, all results obtained from the analysis of standard compounds being within +/- 0.3% absolute error. Digestion in an open tube with perchloric and sulphuric acids gives satisfactory results for bismuth compounds but erratic and often low results for aluminium and copper compounds.     

Differential controlled-potential coulometry: application to the determination of uranium

Differential controlled-potential coulometry has been investigated as a high-precision analytical technique using the reduction of uranium (VI) in 0.5 M sulphuric acid at a mercury cathode. A relative standard deviation of 0.009% was obtained with 30–120 mg samples of uranium and the method was applied to the comparison of uranium standards.     

Preconcentration of lead in biological matrices for graphite furnace atomic absorption spectrometry

Lead was transferred by a two-step extraction procedure from complicated biological matrices into an aqueous solution. Thereafter, lead could be accurately determined in the aqueous solution without interference by graphite furnace atomic absorption spectrometry (GFAAS). Biological samples were digested sequentially by a mixture of sulphuric acid and nitric acids and a strong oxidant, potassium peroxodisulphate. Lead was extracted by dithiocarbamate in chloroform from the digest solution and subsequently back-extracted into a mercury(II) solution. Matrix materials such as chloride, phosphate and sulphate, which were known to cause serious interference in the determination of lead by GFAAS, could be eliminated in the preconcentration procedure. Close to 90% recovery of lead was achieved. The proposed procedure was applied for the analysis of several NBS biological standard reference materials containing lead in the mg kg^?1 range and satisfactory results were obtained.     

Anion-exchange separation and spectrophotometric determination of molybdenum and tungsten in silicate rocks

A combined ion-exchange spectrophotometric method has been developed for the determination of molybdenum and tungsten in silicate rocks. After the decomposition of samples with a mixture of sulphuric, nitric and hydrofluoric acids, traces of molybdenum and tungsten are separated from other elements by anion-exchange in acid sulphate media containing hydrogen peroxide. The adsorbed molybdenum and tungsten can easily be stripped from the column by elution with sodium hydroxide-sodium chloride solution. The adsorption and desorption steps provide selective concentration of molybdenum and tungsten, allowing the simultaneous spectrophotometric determination of the two metals with dithiol. Results on the quantitative determination of molybdenum and tungsten in the U.S. Geological Survey standard samples are included.     

Determination of mercury in zinc ore concentrate reference materials using flow injection and cold-vapor atomic absorption spectrometry

A flow-injection, cold-vapor atomic absorption spectrophotometric method was developed for the determination of trace amounts of mercury in a proposed zinc ore concentrate Standard Reference Material (SRM 113b). The samples were digested with nitric and hydrochloric acids in closed Teflon digestion vessels. The experimental details for sample preparation and the flow injection method are discussed. The effect of matrix and various acid concentrations on the extraction and subsequent analysis of mercury were also studied. The method has a detection limit of 0.08 mug Hg/g in the sample. A certified reference material (CZN-1) was analyzed and the results obtained agreed well with the certified value.     

Anion exchange studies of indium(III) in malonate and ascorbate solutions separation from mixtures

Summary Systematic studies are presented on the anion-exchange behaviour of indium on Dowex 21K in malonic acid and ascorbic acid solutions. Hydrochloric, sulphuric, nitric and perchloric acids, also sodium and ammonium nitrate at different concentrations were tested as eluants in the two systems. Their efficiency was evaluated in terms of elution constants. Methods have been developed for the separation of indium from several elements in malonate as well as ascorbate media with the technique of selective sorption, selective elution or by gradient elution.     

Acid decomposition method for visual colorimetric determination of molybdenum in geochemical exploration

A mixture of nitric and sulphuric acids is used for the decomposition of geochemical samples. Determination of molybdenum at the μg g^?1 level is effected by visually comparing the colour of the thiocyanate complex. The acid medium seems to be well suited for the colorimetric determination of molybdenum. The same solution can be used advantageously for atomic absorption measurements for larger amounts of molybdenum. The method is suitable for batch analysis and results in a high throughput.