The precision of determinations of zinc content of food

Seven different types of foodstuff (containing 3-100 ppm Zn) were each analysed for zinc by colorimetry, polarography and atomic-absorption spectroscopy. All the techniques yielded similar values for the zinc content of a given sample, but atomic-absorption spectroscopy had a smaller average coefficient of variation.     

An investigation of a flameless atomic-absorption method for determination of aluminium, calcium, iron and magnesium in sewage sludge

The methods currently used for the determination of aluminium, calcium, iron and magnesium in sewage sludge are time-consuming. A rapid flameless atomic-absorption procedure, utilizing homogenization of diluted samples as the only pretreatment, has been compared with wet and dry analytical methods followed by flame atomic-absorption analysis, in a statistically designed experiment. Low-sensitivity (secondary absorption) lines have been used for the flameless analysis. The flameless atomic-absorption method described is better than all the other methods tested, with the exception of the nitric-perchloric-hydrofluoric acid digestion procedure. The time saved is substantial and the method could be used advantageously for routine analysis.     

Characterization and elimination of the interfering effects of foreign species in the atomic-absorption determination of iron

The inhibition-release titration method has been used to study interference effects in flame atomic-absorption determination of iron. Interferences from anions, cations and complexing agents with the atomic-absorption of iron when a stoichiometric air-acetylene flame is used, can be obviated by a preliminary treatment of the sample solution with sulphosalicylic acid to convert the iron into the same complex before aspiration, thus giving a constant environment for the iron in the flame processes.     

Determination of silver in copper and lead metals and alloys and in zinc and selenium by atomic-absorption spectrometry after separation by extraction of the tri-n-octylmethylammonium-silver bromide complex

A simple and sensitive combined solvent extraction and atomic-absorption spectrometric method has been developed for the determination of silver in copper and lead metals and alloys and in zinc and selenium. Optimal conditions have been established for the extraction and determination of silver. Silver is extracted as the tri-n-octylmethylammonium-silver bromide complex and determined by atomic-absorption spectrometry by spraying the extract directly into the flame. As little as 0.2 mug of silver in a sample can be determined.     

A comparison of methods for the determination of platinum in ores

Fire-assay and wet-extraction methods of determining platinum in ores have been evaluated. The fire-assay procedure using lead as a collector was used in combination with flame and flameless atomic-absorption, emission spectroscopy and X-ray fluorescence. In this last method flattened silver beads were analysed directly, whereas for the other methods the beads were dissolved in aqua regia and the solutions made up with concentrated hydrochloric acid before analysis. The wet procedures involved treatment of the ores with acids and subsequent analysis by flame atomic-absorption or by spectrophotometry after treatment with tin(II) chloride. Chromatographic, ion-exchange and solvent-extraction procedures were used to isolate platinum from base metals, the other platinum metals and gold. Results for each ore by fire assay-flame atomic-absorption, fire assay-emission spectroscopy, and wet extraction combined with spectrophotometry, showed no difference at the 99% confidence level. X-Ray fluorescence and flameless atomic-absorption results tended to be high and low respectively. The most precise method was wet extraction followed by spectrophotometric determination. Emission spectroscopy and X-ray fluorescence generally yielded the poorest precision. Wet-extraction methods were time-consuming and since no advantage was gained in accuracy over the fire-assay methods, a combined fire assay-flame atomic-absorption system was the preferred method of analysis.     

Determination of tellurium in copper, lead and selenium by atomic-absorption spectrometry after extraction of the trioctylmethylammonium-tellurium bromide complex

A simple, rapid and sensitive combined solvent extraction and atomic-absorption spectrometric method has been developed for the determination of tellurium in copper, lead, selenium and blister copper. Tellurium is extracted as the trioctylmethylammonium-tellurium(IV) bromide complex into butyl acetate and determined by flame atomic-absorption spectrometry of the extract. As little as 1 mug of tellurium in a sample can be determined. The extraction of tellurium from hydrobromic acid solution with trioctylamine has also been investigated.     

Determinations of traces of calcium in phosphoric acid and its salts by atomic-absorption spectrometry

A method for the determination of traces of calcium by atomic-absorption spectrometry after extraction into an organic solvent, has been investigated for the determination of traces of calcium in phosphoric acid and its salts. Calcium is extracted as the hydroxy-quinolate complex, the extract is introduced into the flame, and the calcium atomic-absorption is measured. The effects of pH, concentration of reagent, and diverse ions on the calcium extraction were investigated.     

Determination of lead in drinking waters by hydride generation and atomic-absorption spectroscopy, and three other methods

Simultaneous presence of copper and nickel in potable waters interferes with the determination of lead at trace levels by the hydride-atomic-absorption spectrophotometric method. This interference is eliminated by co-precipitating lead with manganese dioxide from acidic solution. The precipitate is dissolved in 0.85% nitric acid and analysed by the automated hydride-atomic-absorption method. This method has been applied to 22 representative water samples and results compared with those obtained by using differential pulse anodic-stripping voltammetry, flame atomic-absorption and graphite-furnace atomic-absorption spectrophotometry. The precision of the three methods is reported and their accuracy checked by the analysis of reference standard water samples. The sensitivity of the three methods is of the order of 1 mug/l., compared to 100 mug/l. for flame atomic-absorption. The merits of each method are discussed.     

Improved tribenzylamine-silver bromide extraction/atomic-absorption spectrophotometric method for the determination of silver in ores, related materials and zinc process solutions

An improved tribenzylamine extraction/atomic-absorption method for the determination of silver in ores, related materials and zinc process solutions is described. The method, which involves the separation of silver by a single methyl isobutyl ketone extraction of the tribenzylamine-silver bromide ion-association complex from ~ 0.5-2M sulphuric acid-0.14M potassium bromide, is simpler and more rapid than a previous method based on a triple chloroform extraction of the complex. Silver is stripped with 12M hydrochloric acid containing 1% thiourea as a complexing agent. Thiourea is destroyed with nitric and perchloric acids and silver is ultimately determined by atomic-absorption spectrophotometry in an air-acetylene flame, at 328.1 nm, in a 10% v v hydrochloric acid-1% v v diethylenetriamine medium. Cadmium and bismuth are partly co-extracted but do not interfere. Results obtained by this method are compared with those obtained previously by the tribenzylamine/chloroform extraction method and with those obtained by a direct acid-decomposition/atomic-absorption method.     

An indirect atomic-absorption method for the determination of selenium

Because of the difficulty in determining selenium directly, an indirect atomic-absorption method has been developed, based on two selective reactions that lead to the formation of the Pd(DanSe)(2)Cl(2) complex and measurement of the palladium absorption. Reaction conditions, separation techniques, effect of foreign ions, instrumental conditions and sample analysis in the sub-ppm range are described. The method is more sensitive than existing atomic-absorption methods for selenium.     

Matrix modification for determination of selenium in geological samples by graphite-furnace atomic-absorption spectrometry after preseparation with thiol cotton fibre

A graphite-furnace atomic-absorption method has been developed for the determination of selenium in geological samples at or below the mug g level after decomposition of the sample with a mixture of perchloric, hydrofluoric and nitric acids and separation of selenium from the sample matrix with thiol cotton fibre. A few micrograms of palladium are added as a matrix modifier for the atomic-absorption determination. In the presence of palladium the charring temperature for selenium can be raised to 1100 degrees , and the signal enhancement is greater than with other matrix modifiers reported in the literature.     

Rapid determination of nanogram amounts of tellurium in silicate rocks

A hydride-generation flameless atomic-absorption technique is used to determine as little as 5 ng g^-1 tellurium in 0.25 g of silicate rock. After acid decomposition of the sample, tellurium hydride is generated with sodium borohydride and the vapor passed directly to a resistance-heated quartz cell mounted in an atomic-absorption spectrophotometer. Analyses of 11 U.S. Geological Survey standard rocks are presented.     

Indirect determination of cyanide in water by atomic-absorption spectrophotometry

An indirect method for determination of trace cyanide in water by atomic-absorption spectrophotometry is described. Cyanide forms a stable complex anion with Pd in alkaline solution. This complex anion can form an ion-association complex with tetra-alkylammonium ions which can be extracted into n-butyl alcohol with an efficiency higher than 90%. The extract can be analysed directly for palladium (and hence indirectly for cyanide) by flame atomic-absorption spectrophotometry. The detection limit for cyanide by this method is 0.1 mug ml in the n-butyl alcohol extract. Beer's law is obeyed for 0.13-9 mug of CN(-) per ml of n-butyl alcohol. Several foreign ions do not interfere.     

Determination of cadmium in urine by extraction and flameless atomic-absorption spectrophotometry Comparison of urine from smokers and non-smokers of different sex and age

A method is presented for determining cadmium in urine by nameless atomic-absorption spectrophotometry after extraction. The sample is dried, ashed in the presence of nitric acid, and then the residue is dissolved in hydrochloric acid. Cadmium is extracted as its tetrahexylammonium iodide complex into methyl isobutyl ketone. The organic phase is analysed for cadmium by atomic-absorption spectrophotometry with electrothermal atomization. The median urinary excretion of cadmium for smokers aged 50-64 has been found to be 0.7 and 0.75 mug l . for males and females respectively, the values for non-smokers being 0.25 and 0.4mug l .     

Electrothermal atomic-absorption spectrometric analysis of lake waters for Mn, Fe, Pb and Cd

Analyses have been made for trace metals in surface waters from lakes known to be sensitive to inputs of acidic deposition. Electrothermal atomic-absorption spectrometry was used for direct measurement of the low metal concentrations. The studies revealed non-spectral interferences resulting from small amounts of inorganic material in the sample matrix that prevent accurate measurements of Mn and Pb. Several types of interferences were identified by means of a computer coupled to the atomic-absorption spectrometer and procedures to overcome them were evaluated. Matrix modification with nitric acid is required for the determination of Mn. Atomization from a platform inserted within the graphite tube is necessary for interference-free Pb determination.     

Determination of gold in silver, copper, lead, selenium and anode slime by atomic-absorption spectrometry

A simple and sensitive combined solvent-extraction and atomic-absorption spectrometric method has been developed for the determination of gold in silver, copper, lead, selenium and anode slime. Samples are decomposed with hydrochloric and nitric acids, and gold is extracted as the trioctylmethylammonium-gold bromide complex and determined by atomic-absorption spectrometry by direct spraying of the extract into the flame. Optimal conditions for the extraction and determination of gold have been established. As little as 0.5 mug of gold in a sample can be determined. The extraction of gold from hydrochloric or hydrobromic acid solution with trioctylamine or trioctylmethylammonium chloride (or bromide) has also been investigated.     

Precision and linearity of determinations at high concentrations in atomic-absorption spectrometry with horizontal rotation of the burner

The variation in precision of analytical measurements and linearity of analytical calibration curves resulting from a reduction of flame path-length by rotation of the burner head in flame atomic-absorption spectrometry is described. The precision is found to be approximately equivalent to that with the normal burner slot alignment, and the linear range is found to be improved in some cases. The application of burner rotation to determination of zinc in Standard Reference Material 1648-Urban Particulate Matter, is shown to provide precision and accuracy typical of flame atomic-absorption analysis.     

Enhancement of sensitivity in atomic-absorption spectrometry by addition of a graphite lid to a cup furnace

By using a cup furnace covered with a graphite lid, it is possible to enhance the atomic-absorption signal for Cd, Zn, Sb, Pb, In, Cu and Fe in solution and for Pb in tin metal (directly atomized). When the analyte is atomized in the cup furnace, part of it condenses on the lid, from which it can be re-evaporated and atomized to give a second absorption signal and hence greater sensitivity. When the lid is small, so that the temperature lag is short, the initial atomic-absorption intensity is also enhanced. The enhancement is due to an increased residence time of the atomized analyte in the cup.     

Determination of gold, indium, tellurium and thallium in the same sample digest of geological materials by atomic-absorption spectroscopy and two-step solvent extraction

A rock, soil, or stream-sediment sample is decomposed with hydrofluoric acid, aqua regia, and hydrobromic acid-bromine solution. Gold, thallium, indium and tellurium are separated and concentrated from the sample digest by a two-step MIBK extraction at two concentrations of hydrobromic add. Gold and thallium are first extracted from 0.1M hydrobromic acid medium, then indium and tellurium are extracted from 3M hydrobromic acid in the presence of ascorbic acid to eliminate iron interference. The elements are then determined by flame atomic-absorption spectrophotometry. The two-step solvent extraction can also be used in conjunction with electrothermal atomic-absorption methods to lower the detection limits for all four metals in geological materials.