The catalytic effect of sulfhydryl groups on the oxidation of sodium azide by iodine was first described by F. Raschig (214), and F. Feigl (217) utilized it to develop the most sensitive qualitative test for the presence of sulfhydryl containing compounds. The reaction, initiated by mercaptans, sulfides, thiosulfates and thiocyanates, takes place as follows:

2 NaN3 + I2 = 2 Nal + 3 N2

While this equation implies that the sulfhydryl compounds do not take part in the reaction, this is not entirely correct, because simultaneously, the sulfhydryl groups are oxidized by the free iodine. Accordingly, the reaction is carried out in a Warburg apparatus, where 1 ml. of 0.2 M sodium azide and 1 ml. of 0.1 M iodine potassium iodide solutions are mixed, while the sulfhydryl containing solution is kept in the sidearm, and then added to the reagents after temperature equilibrium is reached. Upon complete mixing, there is rapid nitrogen evolution, which, however, ceases within 13 minutes. The amount of nitrogen evolved is found to be linearly proportional to the content of the sulfhydryl groups, and on the average, 1 ml. of urine, 0.05 ml. of blood or 1 ml. of a 3 x 10-4 M sulfhydryl containing solution are amply sufficient for an assay. The method is thus well applicable to the determination of sulfhydryl levels, provided the method is standardized with the appropriate compound to be tested, as the catalytic effect of all mercaptans is not the same. (218)


Fig. 216B. Electrocardiograms, in first lead in rabbits injected intraperitoneally with sublethal doses of different agents. In the group with lipoids with positive polar groups besides other changes, a flattening of the wave T is induced, which contrasts with a more elevated T for the group of lipoids with negative character.