Introduction
Although several polarographic methods for the determination of manganese have been devised, none is applicable to every kind of sample. VON STACKELBERG, KLINGER, t{OCH AND KRATH 1 neutralized an acidic solution of the sample with barium carbonate to precipitate iron(III) and chromium, and measured the height of the cathode manganese(II) wave in the supernatant solution. Large amounts of nickel (and also of many other elements) or cobalt interfere with the measurement of the manganese diffusion current in this procedure, and necessitate a tedious preliminary separation of manganese as the dioxide. In addition, there would appear to be considerable danger of coprecipitation when traces of manganese are being determined.
VERDIER 2 recommended the use of a cyanide medium for the determination of manganese in the presence of chromium(III), copper, iron(II), and zinc, which were said to be polarographically inert in such a medium, and stated that cobalt was the only common interfering element. However, HUME AND KOLTHOFF 4 have since reported that nickel also yields a wave overlapping the manganese wave ~, and that chromium(III) will also interfere to the extent that it is present as ECr(CN)8~ -a.
VERDIER 5 also discovered an anodic wave corresponding to the oxidation of manganese(II) to manganese(III) in a strongly alkaline tartrate solution, and applied this to the determination of manganese in the presence of iron, nickel, and cobalt. Little information has been available concerning the effects of other elements that might be present.
A much more versatile method, developed by KOLTHOFF AND WATTERS 6, involves the measurement of the height of the cathodic manganese(III) wave in a moderately acidic pyrophosphate solution. Chloride, cerium, chromium, vanadium, and large amounts of iron interfere; although the metals can be removed by precipitation with pyridine, the chemical pretreatment required is rather lengthy. It is also disadvantageous that the manganese(III) complex is reduced at an appreciable rate by metallic mercury.
This paper describes a method employing the alkaline tartrate supporting electro-* Based on a thesis submitted by HENRY A. CATHERINO tO the Faculty of the Polytechnic Institute of Brooklyn in partial fulfillment of the requirements for the B.S. in Chemistry degree, 1959.