Partitioning Dissolved Inorganic and Organic Phosphorus Using Acidified Molybdate and Isobutanol

Quantification of P‐mineralization rate in soil using isotopic dilution requires that soluble inorganic 32 P ( 32 P i ) be determined without interference from soluble organic 32 P ( 32 P o ). Therefore, a method is needed to partition 32 P i and 32 P o into physically separate solutions before radiation counting. A previously suggested method of extracting P i into isobutanol with acidified molybdate was tested for efficiency of separation from P o . Inorganic P as KH 2 PO 4 was completely recovered in the isobutanol phase with acid molybdate. Organic P (glycerophosphate) remained in the aqueous phase during the extraction. No P o hydrolysis was observed when sodium phytate, glycerophosphate, ribonucleic acid, adenosine 2′‐ and 3′‐monophosphate, and cytidine 2′‐ and 3′‐monophosphate were extracted, but detectable amounts of adenosine 5′‐triphosphate hydrolyzed. This technique was tested on four Kansas soils, and the levels of inorganic and organic P obtained by this method were the same as those detected by conventional analyses.