Sensitive quantification of gadolinium-based magnetic resonance imaging contrast agents in surface waters using hydrophilic interaction liquid chromatography and inductively coupled plasma sector field mass spectrometry

• A HILIC-ICP-SFMS method for Gd speciation analysis was developed.
• Limits of detection in surface waters are below 0.1 nmol/L.
• Three Gd-based contrast agents were quantified in (sub)nanomolar concentrations.

The application of gadolinium(Gd)-based contrast agents to support medical examinations by magnetic resonance imaging (MRI) results in a large input of Gd into the environment. The long-term effects of the anthropogenic Gd anomaly, especially on aqueous ecosystems, are mostly unknown. The identification and quantification of Gd-based contrast agents in the aquatic environment requires the use of powerful methods of speciation analysis. Therefore, a method employing the hyphenation of hydrophilic interaction liquid chromatography (HILIC) and inductively coupled plasma sector field mass spectrometry (ICP-SFMS) with sample introduction as dry aerosol generated by desolvation was developed. The desolvation resulted in improved limits of detection for the predominantly used contrast agents well below 0.10 nmol/L. This method was subsequently used for the analysis of Gd species in surface waters. Samples from a nature reserve in the city of Münster (Germany), into which the effluent from the city's main wastewater treatment plant enters the environment, were examined. The contrast agents Gd-DTPA, Gd-DOTA and Gd-BT-DO3A were identified and quantified in constant ratios in those samples. The concentrations were found in a range from 0.59 nmol/L for Gd-DOTA up to 3.55 nmol/L for Gd-BT-DO3A. As a result of mass balancing, the contrast agent concentration was found to account for 74–89% of total Gd concentrations, possibly indicating the presence of further Gd species. Nevertheless, there was no direct indication of species transformation by transmetallation reactions resulting in such Gd species. The determination of REE patterns by means of ICP-MS confirmed the results of speciation analysis showing significant Gd anomalies.