Dynamic calibration system for trace analysis in ion chromatography

A dynamic method for the preparation of diluted standards in trace analysis by Ion Chromatography is described. The proposed system uses a diffusion cell that through a capillary tube of known dimension, continuously provides large volumes of highly diluted standard. The diffusion cell setting-up and its working conditions are described, and the advantages and difficulties of the dynamic method are pointed out. Loading the cell with concentrated standard solutions (200-10000 ppm), it was possible to produce diluted Na2SO4 standards in the 0.1-10 ppb concentration range. The cell is able to work for nearly a month before the source amount decreased by 1 %. The linearity of the calibration device is good and the method is free of systematic errors. Under strictly controlled experimental condition, the diffusion cell provides primary standards because it allows to obtain concentrations only depending on its geometry.