Abstract: Serum is passed through a column containing silica gel alkylated with lower alkyl groups. The column is then washed with dilute acid and water and the digoxin eluted with aqueous methanol at a volume less than about the volume of the serum to provide a digoxin concentrate that may be used in assay determinations. The invention also includes a kit comprising in a packaged combination for use in an assay for digoxin (a) a column containing silica gel alkylated with alkyl groups containing 1 to 2 carbon atoms and (b) an aqueous eluent solution which is 50%-70% by volume organic solvent. The organic solvent comprises from 1-4 carbon atoms and from 1-3 heteroatoms selected from the group consisting of oxygen and nitrogen.

Abstract: Serum is passed through a column containing silica gel alkylated with lower alkyl groups. The column is then washed with diluted acid and water, and the digoxin eluted with aqueous methanol at a volume less than about the volume of the serum to provide a digoxin concentrate that may be used in assay determinations.

Abstract: An enzyme-polyidothyronine conjugate for use in determining polyiodothyronine by immunoassay is prepared containing an enzyme which is reversibly deactivated by polyiodothyronine and is reactivated by an antibody binding to the polyiodothyronine of the conjugate. Preferred enzymes are malate dehydrogenase and triose phosphate isomerase.

Abstract: Method and enzyme conjugates are provided for determining physiological amounts of polyiodothyronine in physiological fluid, particularly serum.A homogeneous enzyme immunoassay is provided employing an enzyme-bound-polyiodothyronine having less than about 50 percent of the original enzyme activity, whose activity increases upon binding with a receptor. The enzyme-bound-polyiodothyronine, the unknown suspected to containing a polyiodothyronine, and receptor for the polyiodothyronine are combined in an aqueous medium containing substrate for said enzyme and the enzymatic activity of the solution determined. By comparing the result obtained with results obtained from standards having known amounts of polyiodothyronine, the amount of polyiodothyroninein the unknown can be determined.The enzyme-bound-polyiodothyronine employs an enzyme which is reversibly deactivated by polyiodothyronine, so as to be reactived by receptor binding to the polyiodothyronine.