Since CTC-ice containing carboxymethylcellulose, sodium chloride and sodium bisulfite or sodium thiosulfate is widely used for keeping the freshness of fish in Japan, a practical field method is required for the determination of the concentration, distribution and destruction of the antibiotic in ice. The present study was undertaken to determine whether the chemical methods are applicable to the determination of the CTC concentration in ice, and to improve the acid colorimetric method. 1) When CTC values in ice assayed by the chemical methods were compared with that obtained by the microbiologic method, higher values were always obtained by the Upham et al's method') and the Sakaguchi et al's method, and lower values by the Japan FDA method.2) The Levine's acid colorimetric method3' gave a comparable value to that obtained by the microbiologic method (Tables I-1, 1-3 and I-4). 2) The acid colorimetric method w as improved with respect to its sensitivity and accuracy. The improvement involves using the Beckman spectrophotometer and heating at 80℃. This method was found to yield comparable values to the microbiologic assay values in case of a CTC ice containing sodium thiosulfate, as contrasted to higher values in case of a CTC ice containing sodium bisulfite (Figs. I-6 and 1-7). The improved method is as follows : Place a 50 cc aliquot of sample and of each of standard solution series (1～8 mcg/cc) in separate 100 cc flask and add each a 20 cc aliquot of 20 % hydrochloric acid. Heat for 20 to 30 minutes in a water bath at 80℃. After cooling in running water, fill the mixture up to the mark of flask with distilled water. Measure the absorbancy of the sample by the Beckman spectrophotometer at wave length of 440 mg using a cuvette of 100 mm light path. Prepare a standard curve by plotting the absorbancies of the standard CTC solutions against the corresponding concentrations of CTC. A representative standard curve is presented in Fig. 1-4. From the standard curve find the CTC concentration of the sample solution.
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