Direct quantification of thallium(I) in water by ESI-MS via supramolecular recognition with cryptand[2.2.2]

Thallium, a highly toxic heavy metal, is widely distributed in the environment. The substance poses a grave threat to human health through contamination of the food chain, drinking water, and environmental exposure. Consequently, the monitoring of thallium levels, particularly in water, is of critical importance. In this study, a novel analytical method was developed for the direct quantification of thallium ions (Tl⁺) in aqueous samples. This method is based on the specific supramolecular interaction between cryptand[2.2.2] and Tl⁺, and it utilizes electrospray ionization tandem mass spectrometry (ESI-MS/MS).

The method demonstrated remarkable analytical performance, exhibiting a linear range of 2.5 to 100 μg/L (R² > 0.999), a limit of quantification (LOQ) of 2.5 μg/L, and a limit of detection (LOD) of 0.8 μg/L. The recovery rates exhibited a range from 88.65% to 118.09%, with relative standard deviations (RSD) falling below 10%, thereby affirming the attainment of satisfactory accuracy and precision. It is noteworthy that this method necessitated only 5 μL of sample and did not require any preliminary separation steps. Despite the inhibitory effects exhibited by complex sample matrices, these effects were effectively mitigated through a straightforward dilution strategy. The method was successfully applied to the analysis of 66 real-world environmental water samples.

This work presents a novel tool that enables rapid and reliable detection of Tl⁺ in water samples. Compared with traditional ESI methods for heavy metals, the application of cryptand[2.2.2] makes the developed method more selective and sensitive, since it has strong binding ability and selective to Tl⁺ ion. The study introduces a novel design concept and practical application for the development of supramolecular recognition-based ESI-MS methods for metal ion analysis. These methods hold significant potential for environmental monitoring and related fields.