Purify the salt through an acid ion-exchange column (in H+ form) to give the free acid [1136-89-6], M 224.2, which is obtained by freeze drying and recrystallising from Me2CO/*C6H6, or by adding 2.5volumes of hot CHCl3 (or 20 parts of boiling *C6H6) to a hot solution of 1 part acid and 1.2 parts Me2CO and cooling (m 155-157o, 157-158o). The acid is dissolved in the minimum volume of H2O to which 2 equivalents of NaOH are added and then freeze dried, or by adding the equivalent amount of MeONa in MeOH to a solution of the acid in MeOH and collecting the Na salt, washing with cold MeOH, then Et2O, and drying in a vacuum. [Friedman & Seligman J Am Chem Soc 72 624 1950, Chanley & Feageson J Am Chem Soc 77 4002 1955.] The monosodium salt [1136-89-6] is similarly prepared but by using 1 equivalent of NaOH. The phosphate group is hydrolysed at pH 1.1-5.85 at 70o. [Beilstein 6 IV 4226.] It is a substrate for alkaline phosphatase [Gomori Methods Enzymol 4 381 1957, 128 212 1968], and prostatic phosphatase [Babson Clin Chem 30 1418 1984]. [See p 538 in “Metal-organic Compounds”, Chapter 5, Beilstein 6 IV 4226.]
