Separate determination of ethylenediaminetetraacetic acid and its calcium chelate in foods by colorimetry.

A simple colorimetric method is described for the separate determination of ethylenediaminetetra acetic acid (free EDTA) and its calcium chelate (Ca-EDTA) in commercial foods. The underlying principle of the method is that free EDTA is adsorbed by a cation exchange column, but Ca-EDTA is not under weak alkaline conditions. The sample was homogenized with 0,1 n-NaOH and then subjected to equilibrium dialysis against 0,02 n-NaOH at ambient temperature for a definite time (not less than 12 h). An aliquot of the dialysate was measured into a beaker. After the pH of the solution had been adjusted to 8.5 it was applied to a pre-packed cation-exchange column (Amino-form). Free EDTA was adsorbed by this column, whilst Ca-EDTA passed through it without any loss. For assay of Ca-EDTA, the pH of the eluate was adjusted to 2.5, followed by the addition of an excess amount of CuSO4 to convert Ca-EDTA into Cu-EDTA. This solution was then divided into two portions of equal volume. One portion was subjected to the assay of free copper ions, and the other to the assay of total (the sum of free and chelated) copper ions. The difference between the two values is a measure of Ca-EDTA. For the assay of free EDTA, EDTA adsorbed by the column was eluted with 0.5 n-acetate buffer (pH 5.0), followed by the treatment in the same manner as in the case of Ca-EDTA.(ABSTRACT TRUNCATED AT 250 WORDS)