AbstractIn the present work the degradation of chloroplatinates emitted into the aquatic environment has been investigated in model studies. CE coupled to inductively coupled plasma sector field MS (ICP‐SFMS) was employed as an analytical method of measurement. The CE‐ICP‐MS interface utilized the functional make‐up flow design with a microconcentric nebulizer. [Pt(Cl4)]2– and [Pt(Cl6)]2– were separated within 5 min. During a measurement period of 6 h an excellent reproducibility of migration times (RSD 2.3%) could be achieved. The high sensitivity of ICP‐SFMS resulted in an LOD of 80 ng/L platinum for the two compounds. External calibration using rhenium as internal standard was linear over three orders of magnitude. However, with external calibration a long‐term drift of signal intensity was observed. In order to reduce the uncertainty of the obtained results, quantification of [PtCl6]2– was performed for the first time by species‐specific on‐line isotope dilution MS using 194[PtCl6]2– as spike. The two different quantification strategies were compared in terms of their total combined uncertainty of measurement according to the EURACHEM guideline. The method was employed for monitoring the time‐dependent degradation of [Pt(Cl4)]2– and [Pt(Cl6)]2– in water containing 0 and 2.8 mmol/L Cl– and river water. [Pt(Cl6)]2– was stable whereas [Pt(Cl4)]2– showed rapid degradation following pseudo first‐order kinetics.