A MICRO-METHOD FOR THE DETERMINATION OF BUTYL-ALCOHOL EXTRACTABLE HORMONAL IODINE IN SERUM*†

Abstract

A micromethod for the determination of serum butanol-extractable hormonal iodine, using an ashing technique and adapted to the Beckman DU spectrophotometer, is described. The adaptation of the method to this spectrophotometer has been achieved by employing the inhibitory effect of Ag+ on iodide catalysis of the ceric-arsenious reaction. Chemical kinetics pertaining to the catalytic effect of I- on the ceric-arsenious reaction are analyzed and discussed. Under the conditions of this procedure, the catalytic effect of I- on the ceric-arsenious oxidation reduction reaction follows a first-order rate, and therefore a linear calibration curve can be constructed relating the [image] to the concentration of added I-. Recoveries of freshly prepared thyroxine alone and thyroxine added to serum, using the prescribed procedure, ranged from 92 to 101 per cent. This method effectively eliminates potential contaminants of serum such as mono- and diiodotyrosine, inorganic iodide, and heavy metal.