Improvement in PBI method.

THERE ARE A NUMBER OF VARIATIONS in the methods described in the literature for the procedure by incineration for the determination of protein bound iodine (PBI) (1, 2). Most of these are simple variations of the basic ones described earlier in the literature. After incineration there remains an insoluble portion when the residue is treated with 2N HC1, 7N 112S04, and H20. It appears to be unburned carbon rather than any other substance. The technician is directed to centrifuge this at a high speed for a few moments before withdrawing a sample. Some of the suspension of carbon frequently is not collected in the bottom of the tube and remains like a fine suspensoid (cannot be centrifuged out) in the acid solution. (The solution is not water clear.) This will result in lower values for the PBI since the treated sample will have a lower percentage transmission value or a higher absorbance. The solution can be cleared by ifitering through a cotton plug or fine filter paper. To eliminate this step, varying quantities of pure crystalline KC1O3 were added to the 4 N Na2 CO3 used on the protein before drying. The varying quantities used were 50 mg., 100 mg., 150 mg., and 200 mg./10 ml. of 4 N Na2CO3 thus 5 mg., 10 mg., 15 mg., and 20 mg. KC1O3 were included per sample of 1 ml. serum used. The first tube containing 5 mg. of KC1O3 was the only one in which carbon was left, and this tube had to be filtered or centrifuged. The results were compared with the 4 N Na2CO3 having no KC1O3 added to the sample. The other tubes with increasing KC1O3 (10, 15, and 20 mg./sample) showed progressive rise above the normal value. For example, the standard gave a reading of 54 per cent T, the 5 mg.