Preserving Gadolinium Speciation in Environmental Waters: Establishing Hold Times and Storage Protocols for Reliable Analysis.

Gadolinium (Gd) has emerged as a trace contaminant in aquatic environments due to the widespread use of gadolinium-based contrast agents (GBCAs) in magnetic resonance imaging (MRI) diagnostics. This study evaluates how preservation conditions, including temperature, acidification, and filtration, affect the stability of Gd chelates in three water matrices (deionized water, tap water, and river water) using inductively coupled plasma mass spectrometry (ICP-MS) for total Gd quantification and ion chromatography coupled with ICP-MS (IC-ICP-MS) for individual GBCA quantification. Across all experiments, the linear GBCA was the most susceptible to degradation, with acidification and ion-rich waters accelerating their dissociation, while macrocyclic agents remained more stable. Freezing provided no preservation benefit and sometimes introduced artifacts possibly related to freeze-concentration effects. Filtration improved recoveries in river water by reducing interactions with particulates and microbial activity, and refrigeration slowed degradation but did not fully prevent it in complex matrices. These patterns show that certain preservation choices can alter apparent speciation and lead to underestimation of linear chelates and misinterpretation of GBCA sources. The results provide standardized preservation protocols for sample handling, including avoiding acidification, minimizing storage time, and refrigerating samples when immediate analysis is not possible.