Radiometric determination of sulfate

A radiometric procedure for the determination of sulfate based upon the precipitation of barium sulfate is described, the sensitivity is about 0.01 μg/cm3. Carrier-free 35SO4 is added to the sample to measure the chemical recovery. The sulfate is precipitated with an excess of barium having a known specific activity of 133Ba. The amount of 133Ba determined by gamma counting is directly related by stoichiometry to the amount of sulfate in the precipitate. An intercomparison test at higher levels was performed. The average difference between the two sets of data was 8%. Concurrent measurements of standard sulfate solutions indicated an average difference of 8% providing higher values. The method has been used to analyze rain samples collected at urban, rural and baseline stations. Sulfate concentrations for a baseline sample are tabulated and show a precision of about 3% for replicate measurements. (T.G.)