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A method is described for the determination of antimony, arsenic and tin in foodstuffs in which organic matter is destroyed using a wet-oxidation procedure, except for arsenic in samples of marine origin in which organic matter is destroyed by the dry-ashing technique. Each element is obtained in the highest valency state and converted into the respective normal hydride with sodium tetrahydroborate( 111) , prior to atomisation in a flame-heated silica tube and atomic-absorption spectrophotometric measurement. The optimum conditions for this procedure are discussed and direct and indirect interference effects are described. The accuracy of the procedure is assessed for each element, and where possible the accuracy of the method in application is considered, Standard deviations of the results for levels normally found in foodstuffs have been calculated and derived limits of detection and confidence intervals are given.

A method is described for the determination of total chromium, cobalt and silver in foodstuffs. Organic matter is destroyed by a wet-digestion procedure and the cobalt and silver are concentrated by chelation with diethylammonium diethyldithiocarbamate and extraction into 4-methylpentan-2-one. Chromium is then chelated with pentane-2,4-dione and separately extracted into 4-methylpentan-2-one. The concentrations of the three elements in the extracts are measured by Aame atomic-absorption spectrophotometry. Keywords Chromium detevmination ; cobalt determination ; silver determinat i o n ; foodstufls analysis ; J a m e atomic-absorption spectrophotometry Chromium as chromium(II1) is a recognised essential element in human nutrition. Cobalt is said to be unique in that only one combined form, cyanocobalamin or vitamin B,,, is physiologically active in man.l No other functions for cobalt in the human diet have been clearly established, although dietary cobalt is utilised by ruminant animals. Silver appears t o have no known essential function in human physiology but is a possible contaminant of foodstuffs.Recently described methods for the trace analysis of chromium in various matrices include electrothermal atomic-absorption spectrophotometry following extractive concentration of sea water,, flame atomic-absorption spectrophotometry combined with direct extraction from hydrochloric acid s ~l u t i o n , ~ flame atomic-absorption spectrophotometry following extraction of the ammonium tetramethylene dithiocarbamate (ammonium pyrrolidine dithiocarbamate, APDC) complex or the pentane-2,4-dione (acetylacetone) complex for biological materials or sea gas-chromatographic methods for serum, and neutron-activation analysis for biological materials.* Methods used for trace analysis of cobalt are flame atomic-absorption spectrophotometry after APDC chelation and extraction for vegetables* and neutron-activation analysis for biological materialsg Procedures used hitherto for the trace analysis of silver include conventional atomic-absorption spectrophotometry,lo9l1 electrothermal Delves cup atomic-absorption spectrophotometry,12 plasma emission spectroscopy13 and neutron activation ana1y~is.l~ An estimate of the human intake, in the UK, of each element can be calculated from the results of the examination of the diets that constitute the UK total diet survey.15 Each diet consists of homogenates of nine classes of food, namely cereals, meat, fish, fats, sugars and preserves, root vegetables, green vegetables, beverages and milk from regions of the UK. A procedure was required for the measurement of levels of the three elements in each of these representative food groups.Figures for levels of silver in foodstuffs have rarely been reported. Method ReagentsSolutions should be prepared with distilled water.Williams Ultrar or an equivalent grade is recommended.All reagents should be of a suitable reagent grade, free from the elements being determined.

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A method is described for the determination of total copper, iron, manganese and zinc in foodstuffs. Organic matter is destroyed by wet oxidation and measurement is made directly upon the sulphuric acid digests by flame atomic-absorption spectrophotometry . In the measurement, direct interferences from the inorganic species found in foodstuffs are shown to be a function of burner design and usage. Elimination of these interferences may be achieved for optimum conditions of use, thereby avoiding systematic bias. Isolation of the sources of variation during measurement reveals indirect interferences that enhance the standard deviation of measurement, despite individual presentation of solutions. The accuracy of the method in application to foodstuffs is assessed+for the levels of each element normally present. The standard deviations of results are compared with those for measurement alone and the further influence of indirect interferences on the former is inferred. Derived confidence intervals and limits of detection are given for each element.

An investigation into the extraction of dichlorvos from stored grain and satisfactory storage conditions for samples received for analysis has been carried out using [3ZP]-dichlorvos. It has been shown that samples can beeffectively stored at -17" C and that methanol can be used for the extractable dichlorvos but does not remove the organophosphorus residue bound to the grain.

The early growth stages of chemically reduced cobalt on thin Formvar substrates were examined by electron transmission microscopy. The growth characteristics were examined as a function of the average effective thickness and the deposition rate (1 Å/sec. to 6 Å/sec.). The chemical reduction method is essentially a controlled autocatalytic reduction of cobalt ions from solution by hypophosphite ions in the presence of a catalyst (Co, Ni, Pd, Al). Thin Formvar films prepared on a glass base were indirectly catalyzed with palladium by immersion in a stannous chloride solution, rinsing and immersing in a palladium chloride solution.

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