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An atomic absorption spectroscopic method is described for the quantitative determination of 0.0005–0.01% (5–100 ppm) copper and nickel in tea. After acid decomposition of the organic material, the sample is aspirated into an air-acetylene flame. Radiation at 324.7 nm from a copper hollow cathode is passed through the flame, and the attenuation is measured. The measurement is also made with radiation at 232.0 nm with a nickel hollow cathode. The spectrophotometer is calibrated with known concentrations of copper and nickel in the presence of a matrix similar to that of the samples. The method is applicable to all teas regardless of their geographical origin. Results from 7 collaborators on 6 samples are given. For one sample from 7 collaborators the following mean standard deviations were obtained for 32 determinations: copper 19.5±1.7 ppm and nickel 26.0±1.0 ppm. The method has been adopted as official first action.

Atomic absorption spectroscopy is one of several analytical tools which can be applied to the determination of less than 20 ppm quantities of copper and nickel in tea. A rapid and accurate atomic absorption method is described which is sensitive to these elements at the levels of interest. After the decomposition of organic matter by oxidation with nitric and perchloric acids, or by dry ashing, a solution is obtained which contains only a few major elements. An average matrix composition is determined and synthetic standards for copper and nickel which are free of potential interferences are prepared for a calibration curve. Tea leaves have been analyzed chemically and by X-ray and optical emission spectroscopy in order to evaluate the accuracy of the atomic absorption method. The average of 50 determinations gives a mean of 11 ppm nickel and 32 ppm copper with standard deviations of ±1.6 σ and 1.8 σ, respectively. The method should be applicable to most organic material.

The use of ammonium perchlorate increased the usefulness of the hydrogenargon-entrained air (H2AA) flame. Arsenic, lead, tin, copper, bismuth, cobalt, iron, nickel, antimony, zinc, and selenium were studied. Copper, cobalt, iron, and nickel gave no signal in the relatively low temperature of the H2AA flame. The presence of ammonium perchlorate produced a signal which allowed these elements to be readily detected with a response greater than is obtained with an acetylene-air flame. The presence of a copper, iron, or nickel matrix obliterates the signal from elements studied in the H2AA flame. The presence of ammonium perchlorate does not completely eliminate the matrix effect.