Determination of orthophosphate in soil containing excess pyrophosphate

Abstract
A sensitive colorimetric method of determining orthophosphate in soil that contains excess pyrophosphate is described. A dilute HCl: H2SO4, solution is used to extract orthophosphate from soil. Subsequent determination of orthophosphate in the extractant is performed by formation of a blue phosphomolybdate complex that is separated from the pyrophosphate present by use of a diethyl ether: amyl alcohol solvent. The method is accurate and precise, and gives quantitative recovery of orthophosphate added to soil containing pyrophosphate.