Determination of iodides in food red Nos. 3 and 105 by ion chromatography

Ion chromatographic methods with monitoring by measuring conductivity (CD method) and UV absorption at 215nm (UV method) are presented for the determination of inorganic iodides in Food Red No. 3 (R3; C. I. 45430, C. I. Food Red 14) and Food Red No. 105 (R105; C. I. 45440, C. I. Acid Red 94). After decolorization through a commercial ion-exchange cartridge, R3 and R105 dissolved in water were ion-chromatographed under two operating conditions (CD method, the same as described previously; UV method, TSK-gel IC-Anion PW with Tsk-guard IC-A column with gluconate-borate buffer mainly containing 1.3mM sodium gluconate, 1.3mM sodium borate and 30mM boric acid). The recoveries of NaI (0.118mg) added to R3 and R105 standards (30mg) were 104.3 and 106.3% (CD method), and 97.1 and 101.2% (UV method), respectively. Thirty-one commercial samples of R3 and nine commercial samples of R105 were analyzed by the CD method. All of the commercial R3 except for three samples contained inorganic iodides calculated as NaI above 0.02% (the determination limit) and the highest and average contents were 0.26 and 0.064%, respectively. As for the commercial R105, the contents of inorganic iodides were determined to be 0.06-0.26% and the average was 0.12%. The iodide content averages classified according to manufacturers show large differences for both colors, taking account of their standard deviations. Since we observed increases of inorganic iodides in the solutions of R3 and R105 after storage, the differences might derive from the manufacturing conditions used by each maker during the synthesis of their colorants.