Indirect ultra trace determination of aminopolycarboxylic acids in surface water using ion exchange chromatography coupled on-line to inductively coupled plasma mass spectrometry

An indirect method for the determination of ultra trace amounts of aminopolycarboxylic acids in surface water with a minimum of sample preparation was developed. It is based on the addition of a metal ion to the water sample in order to transform the chelating reagents into negatively charged complexes. These are separated by means of ion exchange chromatography and the metal inside the complex is detected by on-line coupled ICP-MS. Iron and indium as two metal ions of the nominal charge of +3 were investigated, whereas In3+ provided the best results in terms of sensitivity with detection limits in the lower ng/l range. The trivalent complexing agent NTA cannot be determined accurately because of the low retention of the complex. The indium and iron complexes of CDTA are strongly absorbed on anion exchangers and showed retention time of over 1 h. The use of column-switching reduced the retention time to less than 15 min. The method has been validated against a sample set of 62 samples which have previously been analysed by an external water lab according to DIN EN ISO 16588 using the GC–MS method.