Simultaneous Speciation Analysis of Iodine-, Gadolinium-, and Platinum-Based Pharmaceuticals by HILIC-ICP-MS and Its Application to Wastewaters

The widespread use of pharmaceuticals such as iodine-based contrast media (ICM) for medical imaging and platinum-containing anticancer agents has led to their detection in wastewater and surface waters. These substances are typically found at concentrations up to the µg L⁻¹ level for ICMs and at the ng L⁻¹ range for cancerostatic platinum compounds (CPCs) and gadolinium-based contrast agents (GBCAs). Due to their poor removal efficiency in wastewater treatment plants, these compounds have been observed to contaminate drinking water resources. Gadolinium, for example, has even been used as a tracer to monitor contaminant transfer from wastewater to drinking water systems

To investigate the release, transport, and fate of these compounds in the aquatic environment, highly sensitive analytical techniques are required. The coupling of liquid chromatography (LC) with inductively coupled plasma mass spectrometry (ICP-MS) has been widely employed for such studies, providing both elemental specificity and excellent detection limits. However, achieving simultaneous speciation of multiple classes of contrast agents remains a significant analytical challenge.

A research team from the University of Pau (France) has developed an analytical methodology for the simultaneous speciation of iodine-, platinum-, and gadolinium-based complexes at ultratrace concentrations (∼ng L⁻¹). This task is particularly demanding because the target compounds exhibit diverse physicochemical properties—ranging from neutral to ionic or ionizable species with varying polarities.

Figure: Structure of considered pharmaceuticals

Three HILIC stationary phases were compared: two zwitterionic phases (phosphorylcholine and ammonium–sulfonic acid) and one charged silica phase. The effects of mobile phase composition (organic solvent ratio, salt concentration, and pH) were systematically investigated. Furthermore, dipole moment calculations using density functional theory (DFT) provided insight into the observed separation behavior.

The optimized method was then applied to urban and hospital wastewater samples. Two ICMs (iohexol and iopamidol) and one GBCA (gadoterate) were detected. Gadoterate concentrations were similar in both wastewater types, ranging from 525 to 677 ng L⁻¹ Gd. Iohexol was found only in urban wastewater (30 µg L⁻¹ I), while iopamidol concentrations were about 30 times lower in urban wastewater compared to hospital effluents (134 ng L⁻¹ I).

Conclusions: