Thermal and Potentiometric Titrations of Phytic Acid

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Abstract
Values for the ionization constants and the heats of ionization [.DELTA.Hi] of phytic acid (inositol hexaphosphate) were determined by simultaneous potentiometric and thermal titration in a titration microcalorimeter. The potentiometric results are in substantial agreement with those found by discontinuous titration; the heat liberated from pH 10.4 to 6.8 is essentially that found using a batch microcalorimeter. Ionization of phytic acid may be generally characterized as having 5 groups similar to pK1'' of phosphoric acid, 2 groups similar to pK2'' of phosphoric acid and 4 groups similar to pK4'' of pyrophosphoric acid. A single group has pK'' .apprx. 5 with .DELTA.Hi .apprx. -1.1 kcal/mol.