Abstract
Possibilities for the determination of metals by means of the intensity of the e.s.r. signal of the chelate-fonning reagent, spin-labelled iminomonoxime — 4-oximinomethyl-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl, have been studied. The dissociation constant of the oxime group (p K T a = 9.36 ± 0.08) and the reagent partition constant in the chloroform—water system (log K D = 0.80 ± 0.11) are reported. The reagent extracts copper, cobalt and nickel into chloroform. Copper is extracted as its CuA 2, chelate (log K D = 0.91 ± 0.03; log K ex = -3.35 ± 0.09; log β 2, = 15.8 ± 0.2). Several properties of the spin-labelled and conventional oximes are compared. It is confirmed that a radical-containing substituent produces a strong electron-acceptor effect. Unusual extractive and e.s.r.- spectroscopic behaviour of cobalt is indicated; an adduct of the spin-labelled chelate with atmospheric oxygen seems to be formed. Methods for the determination of cobalt and nickel based on the extraction with spin-labelled oxime into chloroform and subsequent separation of the excess of reagent on a chromatographic column are described. The detection limits are 3 × 10 -7 M for cobalt and 10 -6 M for nickel.
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