FACTORS CAUSING ERROR IN BIOASSAY OF CHLORTETRACYCLINE IN TISSUES

Abstract

In the course of study on chlortetracycline (CTC)-residue in the antibiotic-treated food, a possibility was presumed that CTC-residue of salt-dried fish might give a lower value probably due to the inactivation of CTC by oxidized oil, or might give a higher value due to the growth inhibition of the assay organism by the presence of sodium chloride in a sample extract. Furthermore, experiences in our laboratory revealed that the inhibitory zone size became smaller in hot season. Therefore, the present study was undertaken to modify the procedure so that the method can deal with such sample possessing salt and fatty acid peroxide and also can give a higher sensitivity even at high room temperature.
It was shown that a factor responsible for the inactivation of CTC probably peroxidic free radical occurred markedly when the concentration of acetone was increased. It was observed that when acetone-citrate extractant was employed, salt effect occurred in a sodium chloride concentration range above 2%. It was found that the error due to the presence of salt and the inactivating factor can be removed by employing an aqueous M/50 citrate buffer (pH 5.2) as the extractant of CTC from sample. Assay sensitivity at higher room temperature was increased when the assay plate was refrigerated 30 minutes before and after placing a sample extract into the cylinder.