Spectrophotometric determination of indium in microgramme quantities using eriochromecyanine R and cetyltrimethylammonium bromide

New, sensitive spectrophotometric method of indium determination based on its ternary complex with eriochromecyanine R and with cetyltrimethylammonium (CTA) ions has been developed. Under analytically optimal conditions (pH 5.2, about 10-fold molar excess of eriochromcyanine R and about 50-fold excess of CTA) the molar absorptivity was equal 1.01 x 105 l . mol-1cm-1 at lambdasub(max) = 585 nm. During shaking of aqueous solution with organic solvents the ternary complex decomposes (the ion-associate of eriochromcyanine R with CTA passes into the organic phase). Indium complexing anions as EDTA, citrate, tartrate and several metals-especially beryllium, aluminium, scandium, gallium, iron, uranium, thorium, zirconium and vanadium interfere in the determination. Preliminary extractive separation of indium (e.g. as iodide complex) enables to avoid the influence of interfering metals. The explanation of the role of CTA (cationic surfactant) in the bathochromic shiff of the absorbance maximum of indium complex and in the increase of colour reaction sensitivity has been proposed. (author)