Ultraspurenbestimmung von Aminopolycarbonsäure-Komplexbildnern mittels inverser on-line Kopplung IC-ICP-MS

This work introduces the inverse on-line coupling of IC-ICP-MS based on the example of the analysis of aminopolycarboxylic acid based chelating agents. The on-line coupling of ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP-MS) combines the molecular selectivity of IC with the elemental selectivity and sensitivity of ICP-MS. The on-line coupling of IC-ICP-MS is usually used for the analysis of metals or their species. During this work the main interest was on organic chelating agents, which have been tagged with a metal to make it detectable by ICP-MS. This approach makes the excellent detection limits of ICP-MS also available to organic molecules. An excess of In3+ is added to the samples in order to transform the chelating agents into negatively charged complexes, which can be separated using IC. The detection of the complexes is performed by the ICP-MS, monitoring 115In. The chelating agents examined during this work are NTA, EDTA, DTPA and CDTA. The excess of metal is removed automatically prior to the injection of the sample using the Metrohm Suppressor Module (MSM), in order to avoid a large peak in the hold up volume. To reduce the long retention time of the CDTA-complex from over one hour to a few minutes, the technique of column-switching is used. This method uses a fast and simple sample preparation and gives excellent detection limits in the ng/l range. The results of this method have been validated using water samples which have previously been analyzed by an external laboratory in routine analysis using standard methods.