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Correction of "Tube Contribution" Interference in the Determination of Heavy Metals by X-ray Spectroscopy using the "Additions Technique"¹

ABSTRACT

Cr and W X-ray tubes emitted not only the target characteristic lines but the lines of Fe, Zn, Cu, and Ni as well. Such extraneous radiation, which probably originates primarily from contamination of the tube target by the metals and is referred to as "tube contribution," may lead to erroneous qualitative interpretation of X-ray spectra because peaks of the elements may appear in the spectra when the element is not present in the sample. The additions (or spiking) technique allows matrix problems to be overcome in the quantitative measurement of Zn, Cu, and Ni in soils and other materials, but an accurate estimation of the background under the peak is essential. Because of the "tube contribution" to the line of the element concerned, the background under the peak is increased and results in a positive error with the additions technique if no correction is made. The ratio of the peak to background beside the peak for the "tube contribution," for each element, was found to be nearly constant in different materials free of Zn, Cu, and Ni. Thus, a background that includes the "tube contribution" may be calculated, for unknown samples containing the element concerned, by multiplying the background beside the peak by the ratio factor. Using the additions technique including measurement of the background as described, accurate measurements were made of Zn, Cu, and Ni in soils, sewage sludges, and plant and animal tissues.

¹ Scientific Article No. 2171 and Contribution No. 5141 of the Maryland Agric. Exp. Stn., Dept. of Agronomy, College Park, MD 20742.

² Graduate Assistant and Associate Professor of Soil Science, respectively. Present address of the senior author is, Laboratory of Soil Science, Univ. of Thessaloniki, Thessaloniki, Greece.

Received for publication November 3, 1975. Accepted for publication July 9, 1976.