determination of trace-Level Bromate and Perchlorate in Environmental Samples using two-dimensional capillary Ion chromatography with Suppressed conductivity and Mass Spectrometry detection

Importance of the topic

The accurate measurement of trace oxyhalide anions such as perchlorate and bromate in environmental waters is critical for public health and regulatory compliance. Traditional ion chromatography faces challenges at sub-µg/L levels due to high-salt matrices and limited sample volumes. Capillary ion chromatography (IC), especially in a two-dimensional (2-D) format with on-line matrix removal, offers a path to enhanced sensitivity, reduced reagent consumption, and streamlined analyses of complex samples.

Objectives and Study Overview

This study aimed to develop and evaluate a prototype capillary Reagent-Free™ IC (RFIC™) system with suppressed conductivity detection and tandem mass spectrometry (MS/MS) for the determination of trace-level perchlorate and bromate in environmental water samples. Key goals included:

• Integrating a capillary-scale electrolytic KOH eluent generator and suppressor for low-flow operation.
• Implementing a 2-D separation strategy combining a conventional 4 mm column and a 400 µm capillary column.
• Demonstrating on-line matrix elimination and concentration to achieve part-per-trillion detection limits.
• Coupling the capillary IC to MS/MS for confirmation and simultaneous detection of multiple anions.

Methodology

A prototype RFIC system was configured with the following steps:

1. First-dimension separation on a 4 mm Dionex IonPac AG16/AS16 or AG19/AS19 column at 1.0 mL/min using on-line generated KOH eluent.
2. Timed diversion (cut window) of the target analyte zone onto a capillary concentrator column (400 µm i.d.).
3. Second-dimension elution and separation on a 400 µm × 25 cm prototypical IonPac AS20 capillary column at 10 µL/min.
4. Electrolytic suppression of KOH eluent followed by conductivity detection or post-suppressor mixing with acetonitrile for MS/MS infusion.
5. Optimization of cut windows (e.g., 19–24 min for perchlorate, 7.5–10 min for bromate) and eluent gradients to achieve baseline resolution.

Used Instrumentation

• Thermo Scientific™ capillary RFIC™ system with on-line KOH eluent generator.
• Capillary electrolytic suppressor operated in external water mode.
• Dionex Chromeleon™ software for instrument control and data processing.
• Suppressed conductivity detector optimized for 10 µL/min flow.
• Tandem quadrupole MS with negative ESI and post-suppressor addition of acetonitrile.

Main Results and Discussion

The capillary RFIC system delivered highly reproducible separations of up to 22 anions under gradient conditions (retention time RSDs 0.09–0.18%). Key performance metrics included:

• Perchlorate signal enhancement factor of ~152 in 2-D capillary mode vs. first dimension alone.
• Method detection limits (MDLs) for perchlorate of 0.003 µg/L over a linear range of 0.01–10 µg/L.
• Analysis of drinking and bottled water samples revealed perchlorate levels from 38.5 to 263 ng/L and bromate below 10 ng/L without offline pretreatment.
• Evaluation of well water showed perchlorate at 3410 ng/L, reduced to 3 ng/L after reverse-osmosis treatment.
• MS/MS detection achieved clear identification of 13 inorganic and organic anions at 1–10 µg/L in a high-salt matrix (1500 mg/L chloride/sulfate).

Benefits and Practical Applications

This approach offers:

• Minimal sample preparation through on-line matrix removal and concentration.
• High sensitivity and selectivity for regulated anions at sub-µg/L levels.
• Reduced reagent and salt consumption due to capillary flow rates.
• Continuous operation with automated eluent generation and suppression.
• Compatibility with confirmatory MS/MS detection for complex matrices.

Future Trends and Applications

Advances may include:

• Further miniaturization of IC modules and microfluidic integration.
• Expanded analyte coverage, including emerging contaminants and isomeric species.
• Real-time online monitoring of environmental water systems.
• Enhanced coupling to high-resolution mass spectrometry for structural elucidation.
• Portable field-deployable capillary IC platforms for rapid on-site screening.

Conclusion

The developed two-dimensional capillary RFIC system with suppressed conductivity and MS/MS detection demonstrates exceptional sensitivity, reproducibility, and selectivity for trace-level oxyhalide analysis in environmental waters. Its ability to perform on-line matrix elimination and concentration at low flow rates positions it as a powerful tool for regulatory monitoring and research applications.

References

No specific literature citations were provided in the original document.