A pre-concentration technique for determination of P-32 in natural waters

Artificial P-32 (T-1/2 = 14.28 days) can be used to trace the behavior of a major nutrient, phosphate, in aquatic systems. Although liquid scintillati on or Cerenkov counting of high energy betas of P-32 is very sensitive, its usefulness for low level activities is limited by inefficient pre-concentr ation techniques. We found that precipitation of ZrPO4 is an excellent meth od for pre-concentration of P-32 from natural waters. After acidification ( pH similar to2) of a 1-liter sample, about 1 ml 20 mM phosphate carrier is added and equilibrated with natural phosphates. Excess Zr carrier (about 40 mg) is then added to fully precipitate both the natural and added phosphat es in the sample. The ZrPO4 precipitates are collected onto a Whatman GF/B type filter which becomes translucent in Ultima Gold A/B cocktail. We obtai ned constantly high P-32 recoveries (about 97%) through the entire procedur e for hundreds of samples during a hydrologic tracer test. Furthermore, we could process about one dozen samples per hour, and when counting with a po rtable liquid scintillation counter the results are about 500-fold more sen sitive than direct Cerenkov counting.