Chapter 9 – Chemical Assay of Thyroxine-like Materials1

Publisher Summary This chapter discusses the chemical assay of thyroxine-like materials. The variegated chemical functions present in structure of thyroxine—a tetraiodinated, phenolic, diphenyl ether-linked α-amino acid—have given rise to a correspondingly complex array of chemical procedures for the determination of thyroxine and its relatives. Although some of these present certain aspects of specificity, as the Kendall–Osterberg nitrosation or the Komant diazonium salt reaction, none really is specific. The most sensitive of all, determination of iodine at a fraction of a microgram, is the least specific of all. Separation techniques are of primary importance in any specific analytical procedure. Early dependence upon liquid–liquid butanol extraction has given way to paper or column chromatographic separation, most often employing butanol as moving phase. Of several physical techniques of analysis of compounds related to T4, radioactivity labeling is by far the most often employed, because of its extreme sensitivity.