CATION ANALYSIS BY ION CHROMATOGRAPHY .2. DETECTION METHODS

This paper describes the major detection systems that have been couple d with the cation separation processes in ion chromatography. Conducto metric detection is the pre-eminent method for analysis of alkali, alk aline earth, ammonium and alkylammonium cations. The principles of bot h versions - with and without eluent conductivity suppression - are ex amined from a theoretical (sensitivity, signal linearity) as well as t echnological point of view. Using a membrane chemical suppression clea rly improves detectability. But for both options, the limits of detect ion are shown to be strongly dependent an the conductometer's characte ristics. Absorptiometric defection can be seen as a complementary appr oach, especially dedicated to the analysis of transition metal cations , lanthanides and actinides, but also applicable to alkaline earth ele ments. Two reactional processes can be involved: direct metal complexa tion by the post-column reagent or indirect colorimetric reaction. The corresponding detector response equations are discussed and rite limi ts of detection indicated. Less commonly used methods (UV-visible abso rptiometry fluorimetry refractometry, electrochemical methods, atomic absorption and atomic emission spectroscopies, mass spectrometry) are also briefly described. Their specific interest as well as their limit ations are pointed our.