Factors Influencing the Recovery of Iodine from Protein-Free Samples After Alkaline Ashing

Abstract

Studies were conducted to define the factors responsible for the consistently low and disproportionate stable iodine and 131I recoveries from protein-free biological samples by alkaline ashing and ceric-arsenious colorimetry. It was observed that, in addition to iodine loss during the drying and ashing steps, a variable proportion of the residual iodine is chemically modified and will not catalyze arsenious reduction of ceric ion as efficiently as iodide. It appears that a chemically nonreacting iodine-glass component complex is formed during heating. Iodine loss is minimized by the addition of KOH, and iodine modification by the addition of protein (albumin or gamma globulin) +ZnSO4. Reutilization of etched test tubes after alkaline ashing may enhance the formation of chemically nonreacting iodine. (Endocrinology84: 1526, 1969)