PRECIPITATION OF PROTEINS AS SAMPLE PREPARATION FOR DETERMINATION OF IODINE CONTENT IN EGGS BY SANDELL-KOLTHOFF FLOW INJECTION METHOD

Abstract

In this research, the sample preparation methods based on protein precipitation were investigated and developed for determination of iodine in egg samples. The protein precipitation methods such as adjusting pH, salting out at high salt concentration, sodium dodecyl sulfate (SDS) and trichlroacitic acid (TCA) were studied. After treated, iodine was determined by colorimetric method based on Sandell and Kolthoff reaction. According to the physical observation of treated egg samples, treatment method using SDS and TCA could satisfactorily remove most of egg matrix components yielding colorless solution. According to the signal of iodine obtained by the colorimetric flow analysis method, the treatment method using TCA was the most effective egg matrix removal method for determination of iodine in egg samples. A 400 µg of 1 g/mL TCA at room temperature was used for 0.5 g egg sample. The concentration of TCA, incubation time and temperature for egg matrix removal were optimized. The recoveries of spiked iodine in egg samples after treated with TCA were in the range of 84-109%, relative standard deviation less than 6.4%, method detection limit was 0.58 µg iodine/g egg and method quantitation limit was 0.94 µg iodine/g egg. The method provided more reliable results compared to the conventional alkali dry ashing method.