Analysis of Anions and Oxoanions using Ion Chromatography Mass Spectrometry (IC-MS)

Importance of the Topic

Ion chromatography–mass spectrometry (IC-MS) is an indispensable analytical approach for the precise separation and identification of anions and oxoanions in complex samples. This technique underpins critical applications in environmental monitoring, forensic analysis of explosive residues, and quality control in semiconductor manufacturing by enabling robust detection of both common and trace-level ionic species.

Objectives and Study Overview

This work by Katinka Ruth and Andrea Wille presents a streamlined IC-MS workflow tailored for anions and oxoanions. The authors aim to demonstrate:

• Rapid separation of key anions within 15 minutes.
• Enhanced detection limits through combined conductivity and mass spectrometric detection.
• Automated sample preparation strategies for high-matrix samples.

Methodology and Instrumentation

The method integrates a Metrohm IC system with a Waters SQ Detector 2 under Empower 3 software, featuring:

• Conductivity detection for concentration monitoring.
• Selective single-ion recording (SIR) on the MS for confirmatory identification.
• Metrohm suppressor module compatible with up to 100% organic solvents.
• Inline sample preparation options: ultrafiltration, dialysis, dilution, and preconcentration.
• Diverter valve to direct only analyte fractions to the MS, protecting the detector from matrix overload.

Chromatographic separation employed Metrosep A Supp 7 and A Supp 5 columns with sodium carbonate or hydroxide eluents modified by organic solvents. MS tuning optimized low-m/z detection for small ions (e.g., Cl– at m/z 35).

Key Results and Discussion

Fast baseline resolution of anions including fluoride, chloride, nitrite, bromide, nitrate, phosphate, sulfate, thiocyanate, thiosulfate, and perchlorate was achieved within 15 minutes. Detection limits reached sub-single-digit microgram-per-liter levels:

• Chloride: LOD 3 µg/L, LOQ 10 µg/L.
• Perchlorate: LOD 0.013 µg/L, LOQ 0.04 µg/L.

Trace analysis of perchlorate in water and soil matrices conformed to US EPA 332.0, demonstrating RSD < 4% at 1 µg/L spiked levels. Determination of glyphosate, AMPA and related pesticides using a Metrosep Carb 2 column also yielded reliable quantification at 100 µg/L.

Benefits and Practical Applications

The described IC-MS approach delivers:

• High specificity: Combined conductivity and mass detection confirm analyte identity and mitigate co-elution effects.
• Ultra-trace sensitivity: LODs down to tens of nanograms per liter for critical ions.
• Robustness: Organic-solvent-compatible suppressor and automated sample preparation reduce downtime and manual handling.

Applications span environmental compliance testing, forensic residue screening, agrochemical monitoring, and semiconductor process control.

Future Trends and Opportunities

Advancements likely to enhance IC-MS workflows include:

• Integration with high-resolution MS for broader unknown screening.
• Expanded automation using multi-dimensional sample preparation modules.
• Development of new stationary phases for faster separations and improved peak capacity.
• Machine-learning algorithms for real-time data interpretation and anomaly detection.

Conclusion

This study underscores IC-MS as a versatile, high-performance platform for reliable anion and oxoanion analysis across diverse matrices. The synergy of dual detection, rapid separations and automated workflows supports trace-level quantification with high confidence and throughput.

References

1. Katinka Ruth and Andrea Wille. Analysis of Anions and Oxoanions using Ion Chromatography Mass Spectrometry (IC-MS). Metrohm International Headquarters, Herisau, Switzerland, Poster 8.000.6101EN.
2. US EPA Method 332.0. Determination of Perchlorate in Drinking Water by Ion Chromatography.