Limit of detection in barium sulphate gravimetry for water analysis

Abstract

Sulphate ions in the 1–5 mg l^–1 SO₄^2– range can be determined gravimetrically in 200-ml samples using a large excess of barium chloride. From ten determinations at each of three concentration levels of standard sodium sulphate solution, the analytical calibration function calculated by weighted least squares is x_c(mg l^–1 SO₄^2– found)=(0.093 ± 0.064)+(1.008 ± 0.039)c(mg l^–1 SO₄^2– added) with 95% confidence intervals. The limit of detection is c_L= 1 mg l^–1 SO₄^2–(k= 3). A systematic approach is suggested for determining the limit of detection, by considering the variance of both the blank and the calibration function.