Quantitation of lead-210 (210Pb) using lead-203 (203Pb) as a “Massless” yield tracer

Abstract

Determination of Pb-210 (210Pb) in aqueous solution is a common radioanalytical challenge in environmental science. Widely used methods for undertaking these analyses (e.g., ASTM D7535) rely on the use of stable lead (Pb) as a yield tracer that takes into account losses of 210Pb that inevitably occur during elemental/radiochemical separations of the procedures. Although effective, these methods introduce technical challenges that can be difficult to track and potentially introduce uncertainty that can be difficult to quantify. Examples of these challenges include interference from endogenous stable Pb in complex sample matrices; contamination of stable Pb carrier with 210Pb; and high detection limits due to counting efficiency limitations. We hypothesized that many of these challenges could be avoided by the use of the electron-capture, gamma-emitting isotope, 203Pb as a chemical yield tracer in the analysis of 210Pb.A series of experiments were performed to evaluate the efficacy of 203Pb as a tracer. Four different matrices were analyzed, including a complex matrix (hydraulic-fracturing produced fluids); and samples comprising less complicated matrices (i.e., river water, deionized water, and tap water). Separation techniques and counting methodologies were also compared and optimized. Due to a relatively short-half life (52 h), 203Pb tracer is effectively massless for the purposes of chemical separations, allowing for reduced chromatography column resin bed volumes. Because 203Pb is a gamma emitter (279 keV; 81% intensity), recovery can be determined non-destructively in a variety of matrices, including liquid scintillation cocktail. The use of liquid scintillation as a counting methodology allowed for determination of 210Pb activities via 210Pb or 210Po; and recoveries of greater than 90% are routinely achievable using this approach. The improved method for the analysis of 210Pb in aqueous matrices allows for the analysis of complex matrices, at reduced cost, while providing greater counting flexibility in achieving acceptable detections limits.