Microdetermination of inorganic phosphate, phospholipids, and total phosphate in biologic materials.

A rapid, reproducible, and sensitive procedure for the determination of phosphate in several biologic materials is described Organic phosphate is rapidly converted to orthophosphate by digestion with a nitric acid-calcium ion mixture. The acid destroys the organic material while the calcium ion prevents loss of phosphate or its conversion to an unmeasurable form. Inorganic phosphate can be determined in the presence of labile organic phosphates since phosphate liberated after the color reaction has been initiated cannot interfere by forming further color. Even if phosphate were deliberately added after the color reaction had started, it could not react in the described system. The method may be applied to the determination of phosphate present in ultramicro quantities. It is unnecessary to extract the heteropoly acid complex either to increase sensitivity or to protect the color complex formed from interference of phosphate hydrolyzed during the process of color formation.