COLUMN-SWITCHING FOR DIFFICULT CATION SEPARATIONS

In ion chromatography, samples of very different concentration ratios of ammonium-to-sodium are difficult to quantify since these two cation s have similar selectivities for stationary phases containing commonly used sulfonate or carboxylate cation-exchange functional groups. Thes e cations, therefore, elute in close proximity, making quantification of the ion of lower concentration difficult. For example, in the power generation industry, ammonium is often used as a corrosion inhibitor in cooling waters, and determination of low concentrations of sodium i n the presence of high concentrations of ammonium is required. Convers ely, in environmental samples, it is necessary to determine low levels of ammonium in matrices with high concentrations of sodium. An isocra tic column-switching method using two cation exchange columns of diffe rent functionalities allows either of these determinations in concentr ation ratios greater than 10 000:1. (C) 1997 Elsevier Science B.V.