Determination of phosphorus and sulfur in river- and sea-sediments by X-ray fluorescent analysis

Abstract

Determination of phosphorus and sulfur in river- and sea-sediments by X-ray fluorescent analysis was examined. Since the intensities of X-ray fluorescence of light elements are very much affected by the nature of matrix, correction had to be made. The correction was made by assuming that the ratio of the intensities of the light element in two kinds of matrix should be proportional to the ratio of the intensities of the internal standard element (scandium, in the present work) in the same two kinds of matrix, i.e., I_F(i)/I_F(m)=K·I_Sc(i)/I_Sc(m), where IF(i) and I_Sc(i) are the intensities of phosphorus or sulfur and of scandium in the i th matrix, I_F(m) and I_Sc(m) are those in a standard matrix, and K is a constant dependent on the kind of the light element and the instrumental geometry. The value of K was determined by measuring the intensities of the light elements and the internal standard element in various synthetic matrices (the synthetic samples contained 500 μg of the element and 20 μg of scandium per gram).
The standard matrix was made of silica and boric acid (6 : 4 in mass fraction), and the calibration curves of phosphorus and sulfur were constructed with the standard matrix. Three grams of dried sediment powdered in a mixer-mill were mixed with 2 g of scandium oxide-boric acid powder contained 50 μg scandium per gram.
The intensity of the K line of scandium was measured in the sample, and I_F(i) in the sample was also determined. The latter was converted to I_F(m) by using these values and the above mentioned equation, and the contents of phosphorus or sulfur were determined from the calibration curve.
The recoveries in this method were 109.099.6% for phosphorus and 108.291.2% for sulfur, respectively. The lower limit of determination for both elements was 10 μg per gram. The present method is more rapid and more accurate than any other conventional ones, such as colorimetric and volumetric method. The time required for determination of phosphorus and sulfur was about 20 minutes per sample in contrast with 24 hours usually required by other methods.