Abstract: In a phosphate buffer medium of pH 7.0,an associated compound was formed between CTMAB+ and I-3,which was floated into 5.0 mL of benzene.The compound CTMAB+-I-3 showed an absorption maxima at 365 nm,with red-shift of 15 nm from the absorption maxima of I-3 (λmax=350 nm).Color-fading of the associated compound was observed by the presence of ascorbic acid in the reaction system,and linear relationship between the magnitude of decrease in absorbance (ΔA) and the concentration of ascorbic acid was found in the range within 6.0 μg per 50 mL of solution.Test for precision was made at concentration level of 6.0 μg for 6 determination,RSD found was 1.2%,values of recovery found were in the range 96%-101%.