Determination of iopromide in environmental waters by ion chromatography-ICP-MS

Importance of Topic

The widespread use of the iodinated contrast medium iopromide in medical imaging has led to its persistence and detection in surface waters and wastewater. Its hydrophilic and nonionic nature prevents efficient removal by conventional treatment processes, making accurate monitoring essential. Moreover, during disinfection, iodinated compounds can form toxic byproducts at levels of regulatory concern, underscoring the need for reliable trace analysis.

Objectives and Overview

This study aimed to develop and validate a sensitive, robust method for quantifying sub-ppb levels of iopromide in environmental waters. By coupling ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP-MS), the work seeks to establish method detection limits, demonstrate long-term stability under high-matrix conditions, and apply the approach to real river and wastewater samples.

Methodology and Instrumentation

Environmental water samples were collected from rivers and effluents in California and prefiltered. Automated solid-phase extraction (SPE) with hydrophilic-lipophilic balance cartridges concentrated analytes from 1 L of sample. Elution used methanol and methanol/MTBE solvents, followed by evaporation and reconstitution. Chromatographic separation employed a Dionex AG16 guard column and AS16 analytical column with a NaOH gradient (2–90 mM) at 1 mL/min and 500 μL injection volume. ICP-MS detection used an Agilent 7700x with High Matrix Introduction (HMI) interface and helium collision cell to reduce polyatomic interferences on iodine (m/z 127).

Main Results and Discussion

The method achieved a lower method reporting limit of 0.1 ppb in extracts (≈2 ppt in water samples) with linear calibration over four orders of magnitude (0.1–1000 ppb). Continuous 24 h operation showed stable recoveries within 10% of expected values. Real samples contained iopromide from low ppt to hundreds of ppb, confirming environmental prevalence. Additionally, several unknown iodinated peaks were observed; compound-independent calibration based on iodine response allowed quantification of these species as iodine equivalents, revealing potential novel contaminants.

Benefits and Practical Applications

• Sensitive detection of trace iopromide and other iodinated species.
• Robust long-term operation with nonvolatile eluents via HMI interface.
• Effective interference removal using helium collision mode.
• Capability to quantify unknown iodinated compounds through compound-independent calibration.
• Applicability to environmental monitoring, wastewater impact assessment, and disinfection byproduct studies.

Future Trends and Opportunities

Advances may include high-resolution mass spectrometry for structural identification of unknown iodinated compounds, integration of online SPE for higher throughput, expansion to other iodinated pharmaceuticals, and routine monitoring of iodinated disinfection byproducts. Regulatory interest in I-DBPs may drive method standardization and wider adoption in environmental laboratories.

Conclusion

The coupling of ion chromatography with ICP-MS using an HMI interface and collision cell delivers a highly sensitive, reproducible protocol for quantifying iopromide in environmental waters. With low detection limits, extended runtime, and the ability to detect unknown iodinated species, this method offers a valuable tool for environmental monitoring and risk assessment.

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