Fast analyses of anions in water with microbore columns using a compact ion chromatography system for reduced eluent use

Importance of the Topic

The increasing focus on environmental sustainability in analytical chemistry has driven the development of methods that combine high performance with minimal ecological impact. Ion chromatography (IC) is a central technique for monitoring inorganic anions in water, but conventional setups generate significant volumes of eluent waste and require extended run times. Adopting microbore columns and advanced suppression strategies addresses these challenges, supporting green analytical initiatives and efficient water quality monitoring.

Aims and Study Overview

This application note evaluates the use of 2 mm microbore IC columns in a Thermo Scientific™ Dionex™ Inuvion™ system to:

• Reduce eluent consumption and hazardous waste
• Shorten analysis times to under 10 minutes
• Compare chemically regenerated suppression with electrolytic suppression coupled to a carbonate removal device (CRD)
• Assess method performance for a range of water matrices

Methodology and Instrumentation

Instrumental setup and conditions:

• IC system: Dionex Inuvion IC with integrated regenerant pump and optional heater
• Autosampler: AS-AP
• Analytical column: IonPac AS22 (2 × 250 mm) with AG22 guard (2 × 50 mm)
• Suppressors: ACRS 500 (chemically regenerated) or ADRS 600 (electrolytically regenerated) plus CRD 300 for carbonate removal
• Eluent: 4.5 mM Na₂CO₃ / 1.4 mM NaHCO₃ at 0.5 mL/min, column temperature 30 °C, injection volume 5 µL, run time 10 min
• Standards: 1,000 mg/L single anion stocks; mixed and diluted to 11 calibration levels (0.04–71.43 mg/L)
• Sample preparation: 0.45 µm filtration of water samples

Main Results and Discussion

Separation and sensitivity:

• All seven target anions (fluoride, chloride, nitrite, bromide, nitrate, phosphate, sulfate) were baseline-resolved within 8 minutes under both suppression modes.
• Use of CRD with electrolytic suppression reduced background conductivity and initial water dip, improving peak sensitivity by up to 30% (fluoride LOD/LOQ enhancement).

Calibration and detection limits:

• Linear calibration (R² > 0.99) with relative standard error between 3.4% and 9.8%.
• Limits of detection ranged from 0.76 to 6.58 µg/L (electrolytical) and 1.06 to 19.94 µg/L (chemical).

Robustness:

• Over 500 injections spanning drinking water, wastewater, pond, and aquarium samples showed retention time RSD < 0.25% and peak area RSD < 1.3%.

Sample analyses:

• Drinking water and wastewater samples yielded comparable concentrations with both suppression methods.
• Recoveries in fortified wastewater ranged from 78% to 117%, confirming accuracy in high-ionic-strength matrices.

Waste reduction:

• Microbore column operation reduced liquid waste by more than 50% compared to a conventional 4 mm column.
• Electrolytical suppression in recycling mode eliminated chemical regenerant use, further cutting waste and chemical handling.

Benefits and Practical Applications

This approach delivers:

• Faster throughput (< 10 min per run) for routine anion analysis
• Substantial decrease in eluent and regenerant consumption
• Compliance with U.S. EPA Methods 300.0 and 300.1 for inorganic anions
• High robustness and reliability across varied water matrices

Future Trends and Applications

Continued advances may include:

• Extension of microbore IC to additional ionic and polar analytes
• Integration with automated sample preparation and data analysis workflows
• Development of even lower-dead-volume consumables and greener suppressors
• Broader adoption of electrolytic suppression and miniature columns in environmental and industrial monitoring

Conclusion

The implementation of 2 mm microbore columns in an Inuvion IC system, combined with chemical or electrolytic suppression, offers a compelling green analytical solution. It achieves rapid, high-resolution anion separations, reduces hazardous waste by over half, and maintains robust performance across diverse water matrices. Electrolytic suppression with CRD further streamlines operations by eliminating chemical regenerants.

References

1. Dionex IonPac AS22 FAST IC column. Thermo Fisher Scientific. Accessed 10/22/2024.
2. Thermo Scientific Dionex Carbonate Removal Device 300 (CRD 300) Spec Sheet. Accessed 10/22/2024.
3. Sanchez JM. The inadequate use of the determination coefficient in analytical calibrations: J. Sep. Sci. 2021, 44, 4431–4441.
4. ICH Q2(R1) Validation of Analytical Procedures: Text and Methodology. EMA, 2006.
5. U.S. EPA Method 300.1: Determination of Inorganic Anions in Drinking Water by Ion Chromatography, 1997.