Determination of ²¹⁰Pb in Biological Samples: Anion Exchange Resin Separation Coupled With β-Counting Method

²¹⁰Pb is an important long-lived radionuclide in the ²³⁸U decay series with a half-life of 22.23 years, which shows high radiotoxicity and chemical toxicity and widely exists in the atmosphere, soil, water and biological organisms. ²¹⁰Pb originates from both natural decay of uranium and anthropogenic activities such as coal combustion and phosphate fertilizer production, and it can be concentrated through the food chain and cause continuous internal radiation exposure to humans via diet, so accurate measurement of ²¹⁰Pb in biological samples is essential for radiation exposure assessment, food safety control and environmental ecological research. However, the determination of ²¹⁰Pb in biological samples faces many difficulties including complex matrix, serious interference from coexisting elements and very low activity concentration, traditional methods such as γ-spectrometry, α-spectrometry and liquid scintillation counting have obvious limitations in sensitivity, selectivity or analysis time, and the crown ether resins used in standard methods are expensive and provide unsatisfactory recovery in complex biological matrices, therefore this study aims to establish a low-cost, stable and reliable method for the determination of trace ²¹⁰Pb in biological samples. In this work, a new method for ²¹⁰Pb determination was developed using anion exchange resin separation combined with low background β-counter method, a pretreatment procedure of HNO₃-H₂O₂ digestion followed by ashing and leaching was adopted, samples were digested with concentrated nitric acid and hydrogen peroxide, evaporated to dryness and then ashed at 450 ℃ for 2 h, the residue was leached with 1 mol/L hydrochloric acid and filtered, the filtrate was passed through a 201×7(717) strong-base anion exchange resin column pre-equilibrated with 1 mol/L HCl, the column height-to-diameter ratio was optimized to 15∶2-20∶2 and the flow rate was controlled at 1 mL/min, impurities were rinsed with 1 mol/L HCl and deionized water and lead was eluted with 80 mL deionized water, the eluate was concentrated and converted to lead sulfate precipitate, the precipitate was filtered, washed and dried at 105 ℃ to constant weight, the sample source was kept for more than 30 days to reach radioactive equilibrium between ²¹⁰Pb and ²¹⁰Bi, and the β-counting rate of ²¹⁰Bi was measured with a low background α/β-counter to calculate the activity concentration of ²¹⁰Pb. The method exhibits excellent performance and is verified by seven laboratories, the detection limit is 0.9 mBq/g(ash) which meets the requirements of relevant environmental monitoring standards, the precision is satisfactory with the relative standard deviation(s_r) below 10%(n=6), the trueness is high with relative errors ranging from −17% to 17% and mean relative errors from −3.6% to 0.73%, the optimized separation process effectively removes matrix ions such as Ca²⁺, Mg²⁺, Fe³⁺, and radioactive interferences such as ⁹⁰Sr, the 201×7(717) resin provides high selectivity, low cost and stable recovery for ²¹⁰Pb separation, and inter-laboratory validation confirms that the method has good repeatability and reproducibility. This method is simple to operate and has strong anti-interference ability, it is suitable for rapid separation and accurate determination of trace ²¹⁰Pb in various biological samples, provides reliable technical support for radiation environmental monitoring and food safety assessment, and can serve as a useful reference for the formulation of relevant standard analytical methods.