Sequential suppression for conductivity detection in ion chromatography

Importance of the Topic

Ion chromatography with conductivity detection is a fundamental analytical technique for quantifying ionic species in environmental, industrial, and quality control settings. Reliable suppression of eluent background is critical to enhance sensitivity and lower detection limits by reducing baseline conductivity.

Objectives and Overview of the Study

This work investigates a sequential suppression approach combining a chemical suppressor module (MSM II) with a dedicated CO2 suppressor (MCS). The goal is to evaluate improvements in peak area, baseline stability, and calibration linearity in anion analysis.

Methodology and Used Instrumentation

Anion chromatography was performed using a carbonate/bicarbonate eluent neutralized by a cation exchange suppressor (MSM II), which converts conductive eluents to weakly conductive carbonic acid. Downstream, the MCS unit removes residual CO2 via a gas-permeable membrane under vacuum, further lowering background conductivity.

• Cation exchange suppressor module (MSM II)
• CO2 suppressor unit (MCS) with degasser cartridge
• Analytical column: Metrosep A Supp 5 – 100
• Conductivity detector
• Pumping and valve system

Main Results and Discussion

Introducing the MCS unit reduced baseline conductivity from 10–14 μS/cm to near-water levels, increasing analyte peak areas by 20–50%. Calibration curves exhibited excellent linearity, and common interfering peaks from injection and system memory were effectively eliminated. Detection limits for anions such as fluoride, chloride, nitrite, and nitrate were lowered to sub-2 μg/L levels with just a 20 μL injection.

Benefits and Practical Applications of the Method

The sequential suppression scheme delivers significantly enhanced sensitivity and reproducibility for rapid anion determination. It is particularly useful in environmental monitoring, drinking water analysis, and process control where low-level detection and stable baselines are required.

Future Trends and Opportunities

Further development may focus on integrating suppression and degassing functions into compact modules, extending compatibility with gradient elution, and coupling with advanced detectors like mass spectrometers. Automation and miniaturization could broaden applications in on-site and high-throughput analyses.

Conclusion

The combined MSM II and MCS approach offers a robust solution for reducing background conductivity and improving detection performance in ion chromatography. This strategy enhances peak response, lowers detection limits, and supports reliable quantitative analysis of anions.

References

J. Kleimann, H. Schäfer, K. Viehweger. Sequential suppression for conductivity detection in ion chromatography, Metrohm AG application poster 8.000.6076EN.