Studies on Analytical Method of Thiamine Dilaurylsulfate in Soy Sauce

The methods for the determination of thiamine dilaurylsulfate (TLS) in soy sauce have been developed. TLS is a complex of thiamine hydrochloride (TCl) and sodium lauryl sulfate (SLS). The LS portion was determined by the azure A colorimetric method (AA method). Azure A solution and IN sulfuric acid were added to the sample, LS was extracted with chloroform, and then detected at 640nm. The TCl portion was determined by the fluorimetric HPLC method. TCl was converted to its fluorescent derivative, thiochrome, by adding 1% potassium ferricyanide in 20% sodium hydroxide to diluted sample, and neutralizing with phosphoric acid. The thiochrome thus formed was extracted it with isobutanol and then determined by HPLC. Recovery studies of TLS were performed at 3, 5, 10, 12 and 15 ppm (calculated as LS) fortification levels in the samples with both methods. Average recoveries were 98.04-- 98.89% with the AA method and 91.57-92.53 % with the fluori metric HPLC method. Coefficients of variation were less than 5%. The limits of detection of both methods were 0.7ppm. Twenty-seven domestic and thirty-six imported soy sauce samples were analyzed.No TLS was detected in domestic samples, while eight imported samples were found positive for TLS. The data obtained with both methods were practically identical.