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.