Hamano T, Mitsuhashi Y, Tanaka K, Matsuki Y, Oji Y, Okamoto S
Z Lebensm Unters Forsch. 1985 Jul;181(1):35-9. doi: 10.1007/BF01124805.
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)
本文描述了一种简单的比色法，用于分别测定市售食品中的乙二胺四乙酸（游离EDTA）及其钙螯合物（Ca-EDTA）。该方法的基本原理是，在弱碱性条件下，游离EDTA可被阳离子交换柱吸附，而Ca-EDTA则不能。将样品用0.1n-NaOH匀浆，然后在室温下用0.02n-NaOH进行平衡透析一定时间（不少于12小时）。取一份透析液放入烧杯中。将溶液的pH值调至8.5后，将其应用于预装的阳离子交换柱（氨基型）。游离EDTA被该柱吸附，而Ca-EDTA则无损失地通过。为了测定Ca-EDTA，将洗脱液的pH值调至2.5，然后加入过量的CuSO4，将Ca-EDTA转化为Cu-EDTA。然后将该溶液分成等体积的两份。一份用于测定游离铜离子，另一份用于测定总铜离子（游离铜离子和螯合铜离子之和）。这两个值之间的差值即为Ca-EDTA的量度。为了测定游离EDTA，用0.5n-醋酸盐缓冲液（pH 5.0）洗脱被柱吸附的EDTA，然后按照与Ca-EDTA相同的方式进行处理。（摘要截短至250字）
