Direct analysis of Pb in drinking water by liquid scintillation counting after sulfate precipitation.

Lead-210 in drinking water can be rapidly determined by liquid scintillation counting (LSC) using a new sulfate precipitation method. In this method, Pb was first preconcentrated from water using iron hydroxide co-precipitation followed by sulfate precipitation to decontaminate most of non-alkaline earth elements. The Pb in the sulfate precipitate was then dissolved in strong alkaline solution, while alkaline earth elements (Sr, Ba, Ra) were separated as the sulfate/carbonate precipitate. To optimize the method, the influences of different acids and sulfate concentration on sulfate precipitation as well as the effects of pH, the added SO/CO concentrations and the Sr/Ba contents in the sulfate precipitate on the dissolution of PbSO were studied. In addition, X-ray fluorescence (XRF) analysis was applied for rapid determination of the chemical recovery and triple-to-double coincidence ratio (TDCR) quench correction curve for counting of Pb by LSC was established. The method was validated using 5 L of tap water samples and minimum detectable activity concentration (MDC) of ∼0.016 Bq·L was achieved, which is sufficiently sensitive to meet the guidance level of 0.1 Bq·L for Pb in drinking water as recommended by the World Health Organization (WHO).