Determination of sulfate in seawater and natural brines by 133Ba and membrane dialysis

Dissolved sulfate is determined by precipitation with the radioisotope ¹³³Ba and counting of the precipitate on a scintillation counter. Precipitation is carried out in dialysis bags; excess ¹³³ Ba is removed via diffusion by soaking the bags in distilled water for 12 h, and the bags are then placed directly in the well of the scintillation counter. The procedure eliminates previous errors caused by washing and transferring of the precipitate and permits analysis of 0.5–3,000 µg·ml⁻¹ sulfate in a 1.0-ml sample. The detection limit is increased by simply increasing the sample volume up to 5.0 ml. The technique is interference-free in natural waters ranging from freshwater to brines of 1.5 times the salinity of seawater.