Production of copper(I) halide emission spectra by MECA

Abstract

THE introduction of copper (II) salts into most commonly used flames gives a green emission. Copper halides give a particularly intense emission, which is used in the well-known Beilstein test for halogens. The spectra from all copper salts, however, are very similar, and consist mainly of diffuse CuOH bands in the region 535–555 nm, a CuH band centred around 429 nm, CuO emission bands between 445 and 492 nm and a copper atom line at 327 nm (ref. 1, and Fig. 1). Copper (I) halide bands are also present when copper (II) halides are used, but are weak. The enhanced emission of the halides, therefore, arises mainly from their great volatility and consequent enhanced production of exited CuOH, CuO and CuH molecules, rather than greatly enhanced production of copper (I) halide emission. For this reason, pseudohalides such as cyanide and thiocyanate ions also give positive Beilstein tests. The copper (I) chloride emission that has been observed in flames, especially when they are very fuel lean², is very insensitive for use in analysis.