Complementary analytical methods for cyanide, sulphide, certain transition metals and lanthanides in ion chromatography

Abstract

Conventional ion chromatography excludes the analyses of anionic species with pK > 7, and transition metals that can form hydroxide precipitates at neutral pH. These limitations come from the combined characteristics of the suppressor column and the electrical conductivity detector. By suitable selection of the detection system, an extension of analytical limits can be achieved. For fast and accurate analyses of cyanide and sulphide ions, with an electrochemical method involving a silver sulphide based ion-selective electrode and a high pH buffered eluent, the detection limit can reach the p.p.b. level. For determinations of transition and rare earth metal ions, a spectrophotometric detection system is proposed. By post-column mixing with the colour-forming reagents PAR and Arsenazo I, respectively, transition metal and rare earth metal ions can be monitored by measuring the absorbance at 498 and 600 nm. The detection limit can reach the 0.1 p.p.m. level with good precision. The working principle and reaction mechanism of the proposed methods are also discussed in detail.