Special considerations in trace element analysis of foods and biological materials.
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Animals↗
Biomedical subjects
K W Boyer
Publications and source records attributed to K W Boyer.
Interlaboratory variability in trace element analysis.
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Food Analysis↗
Hot leaching of ceramic and enameled cookware: collaborative study.
A hot leach method published by the World Health Organization for determining Pb and Cd in ceramic and enameled ware was collaboratively studied in 14 laboratories. The method consisted of heating a solution of 4% acetic acid at the boil for 2 h in 6 samples of specially glazed ceramic ware and 6 samples of special enameled ware. The acid was allowed to cool and stand in contact with the ware for an additional 22 h. At the end of the 2 h heating period and again at the end of the 24 h period, the leach solution was assayed by atomic absorption spectrophotometry for Pb and Cd. Ruggedness testing before the collaborative study revealed that: (1) the quantity of metal released increased as the average leach temperature approached the boiling point, (2) the quantity of Pb and Cd released from enameled ware increased linearly with time during 7 h of boiling, (3) the concentration of acid could be varied from 2 to 6% with no apparent effect on the amount of metal released, and (4) the room temperature (RT) contact period lasting from 22 to 120 h (after the 2 h heating period) did not increase the amount of metal released. The quantities of Pb and Cd measured by the collaborators at the end of 2 h of heating and after 24 h of total contact were essentially identical. The amounts of Pb and Cd were not related to the quantity of acid solution required to restore the leach solution volume to its initial value after boiling. The collaborative results showed that the period of standing at RT is not necessary and probably can be eliminated from the method. The modified method, which requires analysis of the leach solution immediately after the 2 h heating period, has been adopted interim official first action by AOAC.
Acetates↗
Sampling procedure and determination of lead in canned foods.
A method is presented for improving within-can homogeneity and simplifying the determination of lead in canned foods. The entire content of a canned food product is blended with 2N HNO3 and allowed to stand 16 h; then the sample is again blended and a subsample is taken. The subsample is digested by wet ashing using nitric acid-perchloric acid or nitric acid-sulfuric acid-hydrogen peroxide. The pH of the sample is adjusted with ammonium hydroxide, and the lead is extracted into butyl acetate as the pyrrolidinecarbodithioate complex. Lead concentration is determined by flame atomic absorption spectrometry. Recoveries of lead ranged from 92 to 104% for added 100-mesh lead particulate. Within-sample variability for green beans was reduced from 37% obtained with blending alone to 3.7% using the proposed procedure at the 3.1 micrograms/g added lead level. Variability was 7.6% at the 0.68 microgram/g level and 16.4% at the 0.20 microgram/g level of added lead. The use of nitric acid-sulfuric acid-hydrogen peroxide for digestion has the advantage of not forming a precipitate during the neutralization step, as occurs when nitric acid-perchloric acid is used for dissolution.
Food Contamination↗
Neutron activation analysis of total diet food composites for iodine.
The iodine content of Total Diet food composites was measured using neutron activation analysis. The interfering element chlorine was separated using a modified combustion and gas phase procedure. The average recovery was 94.8% (standard deviation 2.9) for the 10 matrices that were tested. In addition, iodine was measured in National Bureau of Standards Standard Reference Materials, which have no certified values for this element. Preliminary findings of iodine content of adult Total Diet market baskets collected during Fiscal Year 1980 in different regions of the United States ranged from 292 to 901 micrograms/day for a 2900 kcal intake.
Food Analysis↗
Quality assurance in the analysis of foods and trace constituents.
An examination of the results of over 50 interlaboratory collaborative studies conducted by the AOAC on various commodities for numerous analytes shows a relationship between the mean coefficient of variation (CV), expressed as powers of 2, with the mean concentration measured, expressed as powers of 10, independent of the determinative method. Some typical CV values are: drug formulations at a 1% concentration, 2%; sulfonamides in feeds at a 0.01% concentration, 4%; pesticide residues and toxic elements, 10(-6) (1 ppm), 16%; and aflatoxins 10(-8) (10 ppb), 32%. Analytical work at trace levels must be constantly monitored through analysis of reference materials and surrogate samples, and by independent replication.
Aflatoxins↗
Sample homogenization procedure for determination of lead in canned foods.
To improve the homogeneity of canned foods before Pb determination, composited samples or single can contents (150--500 g) are treated with an equal weight of dilute nitric acid, and then thoroughly blended in a high efficiency, probe-type Polytron homogenizer; subsamples are then either dry-ashed or wet-ashed in preparation for analysis. Within-can variability is reduced from the 20--50% coefficient of variation range obtained with conventional blending procedures to a coefficient of variation of less than 5% by using the proceudre described. Precision data for Pb, using both the probe-type and conventional blade-type homogenizers, are compared. The procedure described for Pb determination was used to analyze a number of canned products. Data indicate that the Polytron plus dilute acid procedure improves overall Pb homogeneity for subtle as well as severe initial Pb heterogeneity.
Food Analysis↗
Fortification variability in rat diets fortified with arsenic, cadmium, and lead.
Eleven rat diets fortified with 200 ppm Pb as lead acetate, and/or 50 ppm Cd as cadmium chloride, and/or 50 ppm As as sodium arsenate or p-arsanilic acid for use in a feeding study to determine the interactive effects of the three elements in rats were analyzed to confirm the fortification levels. Gross inhomogeneity was found. After remixing, variability within and among diets was improved but was still unacceptable. Fortification levels of Pb and of As as sodium arsenate could be accurately determined only by taking a very large sample and homogenizing the diet subsamples with a Polytron homogenizer. A review of the recent literature indicates that no standard procedures exist for fortification, mixing, or analysis of animal feeding study diets. Such procedures should be developed and analysis of the diets before and at intervals during a feeding study should be adopted as standard procedure.
Animal Feed↗
Dry ash-voltammetric determination of cadmium, cooper, lead, and zinc in foods.
An analytical method is presented for determining cadmium, copper, and lead by differential pulse anodic stripping voltammetry and zinc by cathodic scan differential pulse voltammetry. Food samples are dry ashed using a sulfuric acid ashing aid, dissolved in dilute nitric acid, buffered at pH approximately 4.3 with an acetate buffer, and quantitatively analyzed using the technique of standard additions at a hanging mercury drop electrode. The quantitation limits (5 times the estimated detection limits) are approximately 5 ng/g for Cd, Cu, and Pb, and 50 ng/g for Zn. Accuracy of the method is established by (a) analysis of NBS Standard Reference Material No. 1577 Bovine Liver, (b) comparison of results obtained by the method described with those obtained by independent analytical methods, and (c) quantitative recovery of analyte metals from fortified, noncanned food samples. Results from an interlaboratory method trial indicate that the method is suitable for the analysis of a variety of food types.
Cadmium↗
A simplified method for the gas-liquid chromatographic determination of methyl mercury in fish and shellfish.
A simple acetone wash of the fish sample which removes lipids and other organic materials replaces the cystein cleanup specified in other methods. Methyl mercury is freed by hydrochloric acid, extracted into benzene, and determined with a gas-liquid chromatograph equipped with an electron capture detector. The method is quantitative for methyl mercury levels as low as 0.10 ppm in fish and shellfish. Ethyl mercury chloride may be used as an internal standard to detect unsuspected error or instrumental parameter variation.
Animals↗
Trace element levels in tissues from cattle fed a sewage sludge-amended diet.
The levels of 20 elements (Al, Ca, Cd, Cl, Co, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, Rb, Sb, Se, V, and Zn) are reported for kidney, liver, muscle, spleen, and brain tissues taken from two groups of six steers per group in a feeding study conducted at Colorado State University. The control group was fed a normal feedlot cattle ration and the test group was fed the same ration amended with 12% (by weight) air-dried municipal sewage sludge. Elemental levels are also reported for the control and test diets, control and test feces, and sewage sludge added to the diet. All samples were analyzed by inductively coupled plasma emission spectroscopy and neutron activation analysis. Brief descriptions of the analytical methods are included. The levels of all metals determined were elevated in the test diet (as much as 19-fold for Cd) compared with the control diet. The levels of Pb and Cd in kidney and of Pb, Cd, and Cu in liver in the test animals were high enough to cause concern from a toxicological standpoint if these tissues were consumed regularly by humans. None of the levels of any of the other elements in the control and test animal tissues were high enough to cause similar concern with respect to human consumption.
Activation Analysis↗