Development of EDXRF techniques for the quantitative multielement analysis of urban dust samples

Abstract

The investigation and monitoring of suspended particulate matter in air require accurate and sensitive multielement analysis of large numbers of samples. In the work described, airborne particles and settled urban dusts were examined by energy dispersive X-ray fluorescence spectrometry with secondary-target excitation. The practical requirements of trace-element determinations in dusts are reasonably satisfied by two techniques. Deposition of fine particles (under 3.5μm) on Nucleopore membrane filters provides thin-film samples, for which absorption and particle-size effects are usually negligible. Calibration is achieved by sputtering of certified NBS standard glasses onto membrane filters. In the destructive “fusion and direct solidification” technique, sample inhomogeneities and particle-size effects are eliminated by fusing the sample with lithium borate in a Pt/Au alloy crucible. La2O3 or WO3, added as heavy absorbers, can reduce the interelement-effects of the thick specimens to a certain extent. A newly developed computer program, based on a modified mathematical expression for the intensity, compensates for absorption and secondary fluorescence effects. It is demonstrated that for some trace elements the background can be easily predicted as a linear function of the incomplete charge-collection of the Si(Li) detector. An intermethod comparison with atomic-absorption results is presented; the results are verified with the NBS Fly Ash standard reference material.