OR/14/067 Silver phosphate precipitation
| Lapworth, D J, Surridge, B, Williams, P J, Heaton, T H E, and Gooddy, D C. 2014. Method for analysing phosphate 18O/16O ratios for waters with high C:P ratios. British Geological Survey Internal Report, OR/14/067. |
The samples were transferred to small 75 ml beakers. To each sample was added:
- 7.5 ml of solution containing 0.2 M AgNO3; 0.7 M NH4NO3; 1.5 M NH4OH
The samples were placed in an oven at temperature 70–80°C. As the ammonia evaporates, crystals begin to form. After 3–4 hours crystals should be visible on the surface of the sample and after 12 hours the precipitation of the dark yellow silver phosphate crystals was considered to be complete. When precipitation is complete the pH of the sample should be between 7.0 and 7.5. If it is higher the samples should be left in the oven longer. If evaporation is drastically reducing the liquid volume of the sample, Ultrapure water may be carefully added. The beakers must not be allowed to dry out, and this step should be carried out in a vented chamber as the reaction releases ammonia.