The determination of iron in organic substances

IN certain experiments on iron metabolism, involving the iron-containing protein of egg-yolk, lecitho-vitellin, we planned to make a large number of iron estimations.To conserve our small supply of protein, the preparation of which had involved considerable time and labour, we desired to cut down the size of the sample analysed to the smallest amount on which an accurate iron deter- mination could be made.The author and colleagues [1930] had already found that the iron content of egg-yolk protein could be accurately determined by the method of Kennedy [1927].The samples then analysed contained about 0 05 mg.iron, an amount somewhat greater than that which we now wished to estimate.The results of a critical study of Kennedy's procedure as the basis of a micro-colorimetric method are recorded in the first part of this paper.The second part is concerned with the determination of small amounts of iron in biological materials by potentiometric titration with titanous sulphate. I. THE DETERMINATION OF MINUTE AMOUNTS OF IRON BY THE METHOD OF KENNEDY.Of the recent methods recommended for the oxidation of organic matter preliminary to estimation of iron in organic materials, [Willstiitter, 1920; Fow- weather, 1926; Kennedy, 1927; Smirk, 1927; Wong, 1928; Elvehjem, 1930] we have found the sulphuric-perchloric acid method of Kennedy to be the most rapid and most convenient.Our adaptation of this method is described later.With some materials "ashing" is the only satisfactory procedure.