Infrared absorption as a consistent method of correcting matrix effect(s) of pellets used in the fluorometric determination of uranium

Abstract

The fluorescent pellet method of uranium determination is a recognized, precise, and accurate technique. What may be termed routine procedures are slow, and consequently expensive, for large-scale geochemical surveys. Attempts to develop a more rapid analytical technique result in a lack of precision which is directly proportional to the magnitude of pellet variability and fluorescence quench effects. Experimental data confirm the argument that these variables constitute matrix effects because they affect the optical, or more specifically the absorptive, characteristics of U-bearing pellets. A method is described whereby this optical variation is quantified using IR radiation to measure what may conveniently be called absorption ( A). The relationship of A to the fluorescence, F, is illustrated for blank pellets, laboratory standards, and lake-sediment standards. From these data a correction procedure that accounts for variations in pellet weight, and hence thickness, pellet crystallinity and quench effects, is developed. In terms of the most important quenching agent, Fe, the optimum range for such a correction is 0.5–10.0%. Using this technique, one hundred plus samples can be analyzed per working day with a precision and an accuracy of the order of ±5%.