RESUMEN
Simultaneous determination of zinc, cadmium, tin, lead and copper was studied in 0.2-0.3M hydrochloric acid-methanol by 1.5 grade differential anodic stripping voltammetry. A stick silver base mercurial film electrode was used as a working electrode. The peak potential of Zn, Cd, Sn, Pb and Cu was distinctly separated each other being -1.05V, -0.74V -0.55V, -0.44V and -0.25V vs SCE, respectivly, in the above solvent electrolyte.Calibration curves of Cd, Sn, Pb and Cu in range of 20 to 600 ng/ml and Zn in range of 0.2 to 4 ug/ml showed linear relation. Canned foods could be analyzed, by dilution with the supporting electrolyte after digestion of the samples with mixed acid. The juice samples could be analyzed directly without digestion, by simple 5-2000 times dilution with the supporting electrolyte. Coefficient of variation and recovey was 6.7-8.0% and 91.2-107% respectively.
RESUMEN
A simple and rapid method was described for determining nitrogen content of a Kjeldahl digest by pulse polarography. The amount of sample needed was as small as 200mg. The digest was diluted and pipetted into a solution of formaldehyde in an acetate buffer. The hexamethylenetetramine produced by reaction between ammonia and formaldehyde was determined electrochemically at -0.9v.This method proved itself a better reproducibility. The recovery rate of nitrogen was 94.5% to 103.1%. Calibration curve of nitrogen in the range of 20 to 120 ?g/ml showed linear relation.Human milk and eleven different food-stuffs were analysed. There was no significant difference between the results by this method and Kjeldahl method.