OR/14/067 Phosphate co-precipitation with brucite (Mg(OH)₂)
| 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. |
This step is commonly referred to in the literature as the Magic precipitation step. 100 ml of each sample was collected in 125 ml nalgene™ bottles. To each sample bottle the following reagents were added, both were dissolved in minimum quantities of ultra-pure water:
- 2 g MgCl₂6H₂O
- 0.4 g NaOH
When added, this formed a cloudy white precipitate (Mg(OH)2). The sample was allowed to stand for at least 2 hours to allow maximum precipitation. If time permits, samples may be left overnight at this stage.
The samples were then transferred to 50 ml centrifuge tubes and centrifuged for 10 minutes at 3000 rpm. The supernatant was then poured off (into a separate nalgene™ bottle) leaving a gel pellet at the base of the centrifuge tube. The bottles of supernatant were labelled and stored for later testing of residual phosphate concentration.