A method for the determination of lead in fish by atomic absorption spectrophotometry and polarography is described. The samples were dry-ashed at 500°C and dissolved in IN HC1; lead was determined by either method. Good agreement between atomic absorption spectrophotometry and polarography was obtained at levels of 1.0 to 10.0 ppm. Over this range the recoveries averaged 96.1% for polarography and 93.8% for atomic absorption spectrophotometry. Twelve species of fresh and salt water fish were analyzed.

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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 ~ 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, non-canned food samples. Results from an interlaboratory method trial indicate that the method is suitable for the analysis of a variety of food types.

When microquantities of 1-naphthyl N-methylcarbamate (I) were nitrosated for 5 min with NaN02 in aqueous acetic acid and hydrolyzed, at a molar ratio of 1 : 10,000 of I : NaN02, the main product found in the resulting yellow basic solution was 1,Pnaphthoquinone monoxime (V). Compound V was formed in direct proportion to the amount of I present.When macroquantities of I and NaNOz (in molar ratios of 1 : 5 ) were used, almost no reaction of I occurred after 5 min. However, after 3 hr or more, 1-naphthyl N-methyl-N-nitrosocarbamate (111) was formed in high yields. Although I11 was unstable a t room temperatures in the solid state and gradually was transformed into 1,l-dinaphthyl carbonate, in microquantities I11 reacted under the same conditions as I to give V. When 1-naphthol wm nitrosated in macroquantities (in a 1 : 1 ratio with NaN02), mainly a mixture of 2-nitroso-1-naphthol (IV) and V was formed. However, when a large excess of NaNOz was treated with microquantities of 1-naphthol, little or no I V or V was observed with a polarograph. A number of model compounds were examined similarly and the results were found useful in formulating a partial explanation of the chemical behavior of I.A colorless intermediate is postulated for the transformation.

The insecticide carbaryl can be determined quantitatively in the presence of a-naphthol by means of oscillographic polarography. A characteristic peak for the hydrolysis product of nitrosated carbaryl is obtained which has a peak potential of –0.45 ± .05 v vs. a mercury pool reference electrode. Using a modified cleanup method, as little as 0.2 ppm of carbaryl residues on certain fruils and vegetables has been determined. Recoveries from fortified crops averaged 95.3% ± 9 . 0% at the 0.2, 5.0, and 10.0 ppm levels. Among those pesticides tested, only o-phenylphenol interfered.