Ultratrace Ion Analysis with Automated Multilevel Calibration

Importance of the Topic

Trace analysis of ions at ultratrace levels is essential in industries such as power generation and semiconductor manufacturing where ultrapure water is critical to prevent corrosion and ensure high product yields. Automated calibration and sample preparation techniques enhance sensitivity and reproducibility, enabling reliable detection of contaminants at ng/L levels.

Objectives and Study Overview

This study demonstrates an automated multilevel calibration approach for ultratrace anion analysis using Reagent-Free Ion Chromatography with Electrolytic Sample Preparation (RFIC-ESP) and an Electrolytic Water Purifier (EWP). The goal is to simplify sample handling, extend sensitivity down to ng/L, and reduce manual errors through automated workflows.

Methodology

• A dual-loop system (10 μL and ~10 mL) meters standards and samples to a concentrator column, enabling simulation of multilevel concentrations from higher μg/L stock solutions.
• Eluent generation via KOH cartridge (EluGen II) produces hydroxide gradients for separation on an IonPac AS15 analytical and AG15 guard column.
• Gradient conditions: 22 mM → 44 mM (0–18 min), 44 mM → 65 mM (18–27.9 min), return to 22 mM at 28 min, hold to 33 min.
• Suppressed conductivity detection using an ASRS-300 suppressor at 180 mA and 35 °C cell temperature, flow rate 1.2 mL/min.
• The EWP provides ultrapure water for sample loading and standard preparation, eliminating the need for a second pump.

Instrumentation

• ICS-2100 integrated RFIC-ESP system
• EluGen II KOH cartridge on EGC-1 for eluent generation
• Electrolytic Water Purifier (dual-chamber resin device, 20 mA)
• IonPac AS15 (4 mm × 250 mm) analytical column and AG15 (4 mm × 50 mm) guard column
• UTAC-LP1 concentrator column
• ASRS-300 anion suppressor and conductivity detector

Main Results and Discussion

• Calibration curves for seven common anions (fluoride, chloride, nitrite, bromide, sulfate, nitrate, phosphate) achieved coefficients of determination > 0.999 across ng/L to μg/L levels.
• Comparison between 10 μL and 10 mL loop injections confirmed accurate volume ratios and consistent quantification.
• The EWP effectively removed background ions, reducing baseline contamination and enabling detection limits below 1 ng/L.
• Application to semiconductor plant water demonstrated reliable detection of anions at sub-ng/L levels, validating system performance in real samples.

Benefits and Practical Applications

• Automated multilevel calibration increases throughput and reduces manual preparation errors.
• Dramatic improvement in sensitivity and reproducibility without requiring additional pumps or complex hardware.
• Applicable to quality control and monitoring in high-purity water systems for power generation, semiconductor manufacturing, and pharmaceutical industries.

Future Trends and Applications

• Integration of real-time monitoring and feedback for process control.
• Expansion to cation analysis and multi-ion detection platforms.
• Coupling with mass spectrometry for enhanced selectivity and confirmation.
• Development of compact, portable systems for on-site environmental and industrial testing.
• Use of AI-driven calibration algorithms to further streamline workflows.

Conclusion

The combination of RFIC-ESP with an EWP and automated multilevel calibration provides a robust, reproducible and highly sensitive approach for ultratrace ion analysis. This system simplifies workflows, reduces contamination risks, and achieves ng/L detection limits suitable for stringent industrial applications.

References

• Sheldon B. Ultratrace Ion Analysis with Automated Multilevel Calibration. Dionex Application Note 2431, 2010.