Determination of phosphate ions in soils

Equipment: Spectrophotometer "Evolution-201"

Goal	Determination of phosphate ions in soils.
Area	Geochemical mapping, archeology, paleogeography.
The maps of phosphates distribution allows to identify: - anthropogenic load in study area; - to identify the possible functional areas of the archaeological site; - to determine the edge line of the ancient water reservoirs.
Sampling	Sampling of soil is performed according to a predetermined plan depending upon the purpose of the study. Mass selected samples should be not less than 20 g from each point.
Samples preparation	The obtained samples are dried in a oven at a temperature of 50-60^oC to remove free water.
The method of phosphate determination	Method for determining phosphates is described in [Bulatov, Kalinkin, 1986]. The method is based on the reduction reaction of the complex to the molybden-phosphoric compounds presumably meets the formula (MoO₂4MoO₃)₂H₃PO₄ with blue color and photometry of solutions at l=590 nm. For photometry spectrophotometer Evolution 201 is used.
Accuracy	The accuracy is 0.1 % content of P₂O₅ in the sample
Reagents required	Hydrochloric acid Sulfuric acid Ammonium molybdate Sodium acetate Phosphate potassium monosubstituted Sodium sulfite Sodium bisulfite Distilled water
The necessary equipment	Spectrophotometer Evolution 201 Hood One-hotplate electric cooker
Literature	M. I. Bulatov, I. P. Kalinkin. A practical guide to photometric methods of analysis. Leningrad, "Chemistry",1986, 432. (in Russian)