SIMULTANEOUS DETERMINATION OF METAL-ION CONCENTRATIONS IN BINARY-MIXTURES WITH A MULTI-LED PHOTOMETER

A compact photometer is based on up to seven different light-emitting diodes whose light is guided into a photometric cell by means of a fib re-optic coupler. The wavelength is selected by switching on the appro priate light source. The application of this multiwavelength photomete r to the determination of binary metal ion samples is demonstrated usi ng model mixtures. Solutions of Fe, Co, Cu, Ni, Cr and Mn were used in combination with several photometric reagents. It was found that the instrument yielded concentration measurements which were usually withi n a few percent of the correct concentration. These results are compar able to reported data obtained with conventional instruments for simil ar measurements. The application of the instrument for simultaneous de termination in flow-injection analysis employing rapid computer contro lled switching of the light-emitting diodes is also demonstrated. A li mitation in the use of light-emitting diodes for the simultaneous dete rmination was found to arise from the fact that in some instances non- linear calibration curves are obtained when employing light-emitting d iodes as light sources. This occurs when the absorptivity of the measu red compound changes over the emission band of the diodes. Multiple re gression analysis is then not easily possible.