The Determination of Thyroxine in the Thyroid Gland

Leland and Foster (1) have recently reported a method for the determination of thyroxine in the thyroid gland which depends upon the selective extraction of thyroxine from the 2 N NaOH hydrolysate of the glandular material by means of butyl alcohol.Harington and Randall (2) have used butyl alcohol for the extraction of diiodotyrosine from the neutralized acid-soluble fraction of an alkaline hydrolysate of thyroid tissue.Several years ago we prepared butyl alcohol extracts of enzyme digests and of alkaline hydrolysates of thyroid glands for experimentation upon animals.Such extracts showed a marked physiological activity but also a high degree of toxicity.This was probably due to the pronounced solvent action of butyl alcohol for various peptides, amino acids, and tarry decomposition products.Other objections to the use of butyl alcohol for the preparation of organ extracts are its high boiling point and its tendency, under certain conditions, to form stubborn emulsions.It seemed for these reasons that ethyl acetate would be a more suitable extraction medium for thyroxine.Kendall (3) reported that the acid-precipitable fraction of an alkaline hydrolysate of thyroid glands is partly soluble in ethyl acetate.Experiments with this immiscible solvent showed that distribution ratios favorable for the differential extraction of thyroxine obtained only when the acidity of the liquid phase was adjusted to about pH 5.For various reasons, which are now being studied, the procedure did not prove entirely satisfactory.When, however, such acid solutions containing thyroxine were shaken with butyl alcohol, it was found that in most cases fully 100 per cent of the suspended thyroxine passed into the organic 269