A New Method for the Microdetermination of Manganese in Biological Materials*

In our studies on perosis in chicks, it was found desirable to be able to determine small amounts of manganese of the order of 0.1 to 10 micrograms. Such a method was necessary for the determination of manganese in bones, blood, and similar materials. The formaldoxime method of Sideris (1) was found unsuitable, as the determination is carried out in alkaline solution. Under these conditions phosphates pr’ecipitate, causing a masking and adsorption of the color. The standard method in which the manganese is oxidized to permanganate and the color thus developed compared with a standard was not sufficiently sensitive. The smallest amount detectable with the use of an Evelyn photoelectric calorimeter and a 5200 ,&. filter was 25 micrograms in 25 cc. In 1913 Dietz (2) and later Feigl(3) and Olszewski (4) described a very sensitive qualitative test for manganese. In alkaline solution manganese dioxide and the permanganate ion oxidized benzidine to give a blue color. With this test it was possible to detect 1 part of manganese in 250,000,OOO. Stratton and coworkers (5) in 1932 and Clark in 1933 (6) suggested the use of benzidine for the quantitative determination of permanganate. However, the blue color obtained was found to fade in 2 minutes, thus seriously limiting the method. Fundamentally, the method depends on the oxidation of benzidine. In dilute solutions of oxidizing agents the meriquinoidal