Quantitative analysis by X-ray microfluorescence and dried spot methodology

X-ray fluorescence is usually regarded as a bulk analytical method with limited sensitivity and requiring several grams of sample for analysis. This typically restricts application of XRF from small mass samples and to concentrations well above the parts-per-million level. The advent of lab based x-ray microfluorescence instrumentation is providing a new tool to address some of these limitations of macro XRF excitation instruments. Dried spot methodology was demonstrated by Meltzer in 1991 that sub-ppm detection limits could be achieved on macro instrumentation. The advantage of using the dried spot technique is that the specimen is within the thin film regime which minimizes matrix effects, thereby allowing almost a universal calibration. It also couples preconcentration with minimized background to increase sensitivity. EDXRF has experienced limited application to radioactive samples due to the background caused by the activity of the sample. This paper will demonstrate the use of x-ray microfluorescence for trace analysis using the dried spot methodology of Meltzer and application to analysis of radioactive samples. The radioactive background is minimized by physically reducing the specimen size and permitting direct analysis of hot samples