Phosphoric Acid → Tricalcium Phosphate

This example demonstrates the use of the method of the present invention in a T-4 test based on dilution of labeled T-4 added to a test sample. Two T-4 controls having assigned or known T-4 values were employed. Serum Sample 1 contained 9.2 μgm % T-4, while Serum Sample 2 contained 15.6 μgm % T-4. 0.1 ml of the serum samples was placed in separate test tubes. To each was added 1 ml of a phosphoric acid solution of calcium chloride containing 36 mg of calcium chloride/ml and having a pH of 1.5. Following mixing, there was added to each tube 0.1 ml of a solution having the following composition: 5 ml of barbital buffer of ionic strength, 0.075, 10 μl of 10% albumin and 5 μCi of I125 labeled T-4. The solution had a pH of approximately 8.6. The resulting solution was mixed and there was then added 2.5 ml of a barbital buffer of ionic strength, 0.075, having a pH of 8.6. Upon addition of the barbital buffer and mixing, there was formed a solid adsorbent comprised of calcium phosphate, the final mixture having a pH of approximately 5. The serum samples were centrifuged and the solid adsorbent in each case counted using a scintillation counter. The results are shown below: