Determination of chloride, bromide and sulfate in color additives by ion chromatography on ceramic carbon column

A method for the determination of chloride, bromide and sulfate in color additives used in drugs and cosmetics (D&C colors) by ion chromatography on a ceramic carbon column was developed; the method was applied to the determination of chloride, bromide and sulfate in D&C colors both by the direct injection method and by an oxygen-flask-combustion method. In the direct injection method, 50 mg of a sample was dissolved in 500 ml of water which was then passed through a Toyopak IC-SP cartridge. In the oxygen-flask-combustion method, several mg of a sample were burned in an oxygen-filled flask containing 20 ml of 2 mM NaOH and 100 mu l of 5% NH2NH2 for determination of bromine, 20 ml of 2 mM NaOH, and 100 mu l of 1% H2O2 as an absorbent for determination of sulfur, and water added to make 100 ml. A 20-mu l aliquot of each sample solution was injected into a ceramic carbon column and eluted with 5% acetonitrile containing 2 mM Na2CO3 and 1 mM tetrabutylammonium hydroxide, under the following operating conditions: flow rate, 0.8 ml/min; column temperature, 40 degrees C; scavenger, 12.5 mM H2SO4. The content of chloride, bromide and sulfate in D&C colors by the direct injection method was found to be lower than 4.3, 1.4 and 0.4%, respectively. The amount of dye molecules determined from total bromine or total sulfur by the oxygen-flask-combustion method was in good agreement with that determined by the titration method or the gravimetric method as directed in The Japanese Standard of Cosmetic Ingredients.