Sodium
35S-cyclamate (
35S-Cy-Na) with a specific radioactivity of 0.10 mCi/mmol was synthesized from cyclohexyl isocyanate and H
235SO
4. Radiochemical and chemical purities of the
35S-Cy-Na were confirmed, and the radiochemical and chemical yields from H
235SO
4 were 24.4% and 48.5%, respectively. The fundamental conditions for isotope dilution analysis were examined for the quantitative determination of sodium cyclamate (Cy-Na) by the use of the
35S-Cy-Na. Three kinds of methods were compared with regard to measurement of the radioactivity of sulfur-35. In the radioactivity measurement of Ba
35SO
4, which was derived quantitatively from
35S-Cy-Na by means of sodium nitrite in an acidic solution, a gas-flow counter for the solid phase and a liquid scintillation counter for the heterogeneous system in a toluene type scintillator with the aid of Cab-O-Sil were compared. In the third method, analysis through the combination of the radioactivity measurement of
35S-Cy-Na and absorptiometric analysis of Cy-Na at 550 nm showed 0.1 mg as the determination limit. In this isotope dilution analysis, the coloration of Cy-Na was made by means of chloranil and hydrogen peroxide, and the radioactivity of
35S-Cy-Na diluted was measured simultaneously using an aliquot of the colored solution. This isotope dilution method was applied to determine Cy-Na in three kinds of canned seafoods which were manufactured before prohibition against Cy-Na as a food additive. The Cy-Na content in canned foods was 0.26% for ark-shell fish, 0.21% for squid, and 0.35% for tuna.
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