High Performance Liquid Chromatographic Method for the Determination of Sodium Alginate in Foods

A method is described for the determination of sodium alginate in foods by high performance liquid chromatography (HPLC).Fat was removed from the sample by acetone extraction and the solution was centrifuged. The precipitate was dissolved in alkaline solution and heated in boiling water to hydrolyze propylene glycol alginate. Then protease and pectinase were added and allowed to react at pH 7-8 and 4, respectively, to decompose protein and pectin. Alginate was precipitated selectively as copper-alginate by addition of cupric sulfate solution. The precipitate was dissolved in ammonia-alkaline solution, then 1, 3-dihydroxynaphthalene (naphthoresorcinol) solution and hydrochloric acid solution containing copper sulfate were added. The mixture was heated in boiling water for 40min, and the reaction product was extracted with butyl acetate and determined by HPLC on a column of Finepak SIL C18 with acetonitrile-water-butyl acetate mixture (75:20:5) as the eluant. The recovery of sodium alginate spiked at the level of 0.1% was 79-99%, and the detection limit was as low as 0.001%. Sixteen commercial samples were analyzed by using this method, and alginate was detected in 5 samples at the level of 0.008-0.088%.