Spectrophotometric Determination of Microgram Quantities of Iron with Nitroso R Salt. II

概要

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An aqueous solution of nitroso R salt is yellow in color at pH below 6.5 having an intensive absorption in the wavelength range below 500 mμ. Above 560 mμ, percentage transmittancy of 2.5×10^<-4> M/L solution was nearly 100. When pH of the solution was raised above about 7.2, a new broad absorption band appeared having a peak at about 580 mμ and the solution appeared greenish. Ferrous iron forms a green complex with nitroso R salt. The absorption maximum in visible range was near 715 mμ. When, therefore, the color was developed at pH above 7.0, the absorption due to the reagent itself should be taken into account. When nitroso R salt was added to ferrous iron and pH of the solution was adjusted to an appropriate value, intense green color developed immediately. But the transmittancy reading shifted gradually from time to time. It decreased in the wavelength range below 660 mμ and above 740 mμ. In the wavelength range between 660 mμ and 740 mμ it increased. Consequently, the spectral absorbancy curve changed its shape on standing. When the solution was warmed on a water bath for about 5〜10 minutes after the color had been developed, constant transmittancy readings were obtained at once. The spectral absorbancy curve coincided with that of ultimate form obtained on standing for a long time. The reaction of nitroso R salt with ferrous iron is seemed to be somewhat complicated. The colored system comforms to Beer's law.
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