AUTOMATIC-DETERMINATION OF LIPOSOLUBLE VITAMINS IN BUTTER AND MARGARINE USING TRITON X-100 AQUEOUS MICELLAR SOLUTION BY LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

An on-line system for the determination of liposoluble vitamins A, D-3 and E in butter and margarine that uses an automatic sample treatment system coupled to liquid chromatography with amperometric detection is described. Butter and margarine samples were dissolved in an aqueous micellar medium using Triton X-100. A flow system with alkaline hydrolysis and solid phase extraction in C-18 cartridges was used. Variables affecting the on-line automatic sample treatment system (sample size, Triton X-100 concentration, stirring time, flow rate, preconcentration, washing and elution times, etc.) were optimized. The vitamins were eluted with a stream of methanol and the richest fraction eluate was automatically injected into the chromatographic system. The proposed method permits the rapid determination of liposoluble vitamins in butter and margarine samples. The recovery factors for the three vitamins assayed ranged between 91 and 95% (n = 10). Additionally, a day-to-day relative standard deviation (10 days) of the method of 2.4-5.8% was obtained for the different vitamins. Results obtained using the on-line method were in good agreement with those obtained by the classical method used for sample treatment.