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An improved method for determination of water-soluble chloride and water-soluble sulfate in food blue No. 1 aluminium lake (B-1 Lake) was developed. The reason for the very poor recovery of sulfate in B-1 Lake was found to be the adsorption of anions on the lake. In order to prevent sulfate adsorption, 0.1M phosphate buffer (pH7.0) was added. As the ratio of B-1 Lake to water decreased, the chloride content apparently increased. A constant value of chloride content in B-1 Lake (3.5%) was obtained by extrapolation.The preparation of test solution and the determination of Cl-, SO42- and I- in B-1 Lake were conducted as follows. Weigh 1.000g of Food B-1 Lake, add 10ml of 0.1M phosphate buffer (pH 7.0) and 90ml of water, and shake for 5 minutes in a mechanical shaker. After filtration, test the solution by ion-chromatography.A good recovery of sulfate was obtained by the proposed method. In a commercial B-1 Lake sample, chloride content was 3.2% and sulfate content was 2.7%, using this method. These values represent total contents of water-soluble chloride and water-soluble sulfate.

A method for determination of the starting materials, [7-hydroxy-1, 3, 6-naphthalenesulfonic acid (TS), G-salt (GS), R-salt (RS), Schaeffer's salt (SS) and naphthionic acid (NA)] and subsidiary colors, [ponceau 6R (P6R), amaranth (R-2) and fast red E (FRE)] in new coccine (R-102) was developed by use of HPLC. The following conditions were used for analysis: column, L-column ODS (4.6mm i. d.×250mm); eluent, gradient elution system of 0.02M ammonium acetate and acetonitrile (hold at 0.02M ammonium acetate for 5min, then 0-30% acetonitrile in 45min); detection for TS, GS, RS, SS and NA at 238nm and subsidiary colors at 510nm.Recoveries of each impurity from R-102 averaged 99.1-103.5%. Ten samples of commercial R-102 were analyzed by the present HPLC method and the impurites were as follows: TS, 0.005-0.044%; GS, 0.044-0.284%; NA, 0.013-0.196%; RS, N. D.; SS, N. D.; P6R, 0.008-0.169%; R-2, N. D. -0.279%; FRE, 0.007-0.100%. The detection limit was 0.001% for each impurity.

A determination method by HPLC for starting materials [sulfanilic acid (SA), G-salt (GS), R-salt (RS), Schaeffer's salt (SS)], intermediates [6, 6′-oxybis(2-naphthalenesulfonic acid) (DONS), 4, 4′-(diazoamino)-dibenzenesulfonic acid (DAADBSA)] and subsidiary colors [3-hydroxy-4-[(4-sulfophenyl)azo]-2, 7-naphthalenedisulfonic acid (RS-SA), 4-[(2-hydroxy-1-naphthalenyl)azo] benzenesulfonic acid (2N-SA), 6-hydroxy-5-(phenylazo)2-naphthalenesulfonic acid (SS-AN)] in sunset yellow FCF was developed. The following conditions were used for analysis: column, Inertsil ODS-2 (4.6mm i. d.×250mm); solvent, gradient elution system of 0.02M ammonium acetate and 40v/v% acetonitrile in 0.02M ammonium acetate; detection, SA, GS, RS, SS and DONS at 232nm, DAADBSA at 358nm and subsidiary colors at 482nm.Recoveries of each impurity from sunset yellow FCF averaged 99.4-102.2%. Sixteen samples of commercial sunset yellow FCF in Japan were examined, with the following results: SA, N. D. -0.170%; GS, N. D. -0.080%; RS, N. D. -0.050%; SS, N. D. -0.281%; DONS, N. D. -0.250%; DAADBSA, N. D. -0.210%; RS-SA, 0.024-3.54%; mixtures of SS-AN and 2N-SA (as SS-AN); 0.015-0.360%. The detection limit was 0.05μg/g for each impurity.

Titanium trichloride titration is employed as the official method of determination of coal-tar dyes permitted under the Japanese Food Sanitation Law. The method was modified to allow the use of automatic photometric titration. The major wavelength of the interference filter corresponded with the specific color of each coal-tar dye. The injection droplet volume, the time interval between an injection and the next injection and the temperature during titration were decided as 30μl, 3sec and 70°C, respectively.When determination of Brilliant Blue FCF by the presented method was carried out repeatedly, the standard deviation was 0.31 and the coefficient of variation was 0.34%. In the determination of Fast Green FCF and Acid Red, the coefficients of variation were 0.19-0.34%.When the determination of four Azo colors and Indigo Carmine by photometric titration were carried out, the standard deviation was 0.08-0.28 and the coefficient of variation was 0.09-0.33%.The method presented here is simple, rapid and accurate, and should be useful for the determination of food coal-tar dyes.