クロラニル酸によるカルシウムの紫外線吸光光度定量

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Ultraviolet absorption photometry was applied to the determination of calcium by chloranilic acid. The ions that gave considerable shifts in the absorption spectrum of chloranilic acid solution in the visible region, such as Mg2+, Fe2+, Fe3+, Al3+, and H+, were found to have very little effect on that in the ultraviolet region. The ultraviolet absorption spectra of chloranilic acid and of metal chloranilates were found to cross each other at definite wavelengths, as if they had some isosbestic points of spectra. Using a wavelength of 248mμ, the interference of coexisting metals in the absorption of chloranilic acid was almost completely avoided, the only problem left being to accomplish perfect precipitation of calcium chloranilate, the solubility of which was small in cold solution. Calcium in water and in plant ash were determined by the authors' method, calcium being directly precipitated from the sample in the former, and from acetic acid extract in the latter. Good results were obtained in the presence of a limited quantity of magnesium.
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