Corrected Equation for the Standard Addition Technique in X-Ray Fluorescence Spectrometric Analysis SIR: A recent use of the standard addition technique for the determination of lead in a n aqueous solution, using X-ray fluorescence spectrometry, revealed a n erroneous equation in the literature for the concentration of the unknown. In his treatise, Bertin ( I ) discusses this technique and refers to the work of Campbell and Carl (2, 3). The original mathematical development is contained in reference ( 3 ) ; in this a n ambiguous statement is given of the concentration of the element being analyzed, after addition of the standard solution, which apparently led to subsequent errors ( I ) . The correct equation, giving the concentration of the element in the unknown solution, may be derived in the following way. Consider a sample of known weight containing a n unknown weight of the element which is to be analyzed. After measuring the X-ray intensity I, (peak - background) due to the element in the sample, a known weight of a standard, containing a known weight of the element, is added to the unknown. The X-ray intensity I,,,, is measured. If it is assumed that the X-ray intensity is linear with the concentration of the element present and is zero at zero concentration, then
I,=KX I,,,
=
K X
weight of element in mixture weight of mixture
=
U,/ITL
