In the case of
chloric acid digestion, we noted that ~75% of the urine samples had a slightly brown color.
Chloric acid digestion is one of the efficient techniques for removing interfering substances (3).
One commonly used method, their "Method A," is based on an initial mild
chloric acid digestion to remove interfering substances, after which the iodine is quantified by its catalytic effect on reducing yellow ceric ion to colorless cerous ion in the presence of arsenious acid (Sandell-Kolthoff reaction).
During these early years, many practicing physicians called it the "blood basal metabolism test!" The method used for the PBI, a modification of the method of Zak, involved the wet digestion of serum with
chloric acid.
Chloric acid was not available commercially and this powerful (and dangerous) oxidant had to be made in the laboratory.