Ion Analysis with Agilent Capillary Electrophoresis Systems

Importance of Ion Analysis by Capillary Electrophoresis

Capillary electrophoresis (CE) has emerged as a powerful technique for the rapid, sensitive and cost-effective separation of charged species. In industrial and environmental laboratories, routine monitoring of small inorganic and organic ions is essential for process control, quality assurance and compliance. Compared with conventional ion chromatography (IC), CE offers faster analysis times, lower buffer consumption, minimal sample preparation and flexible detection modes for analytes lacking native UV chromophores.

Objectives and Overview

This compendium summarizes a range of applications of the Agilent 7100 CE system for ion analysis, including:

• Determination of common cations in food and water matrices by indirect photometric detection.
• Analysis of inorganic and organic anions across diverse fields: power plant water, semiconductor hydrogen peroxide, pulp mill liquors and wafer surface rinses.
• Development and validation of ready-to-use solution kits for cations, anions, organic acids and forensic analytes.
• Establishment of ASTM and SEMI standard operating protocols for CE ion analysis.

Methodology and Instrumentation

The Agilent 7100 CE system is configured with:

• Fused-silica capillaries (50–75 µm id, effective lengths 40–72 cm).
• Diode array detection (DAD) with indirect photometric detection (IPD) using UV-absorbing visualizing reagents.
• Optional contactless conductivity detection (CCD) for non-UV absorbing ions.
• Automated buffer replenishment and flexible method control via CE-ChemStation software.

Sample preparation is generally limited to simple dilution (1:20 to 1:500) and filtration. Capillary conditioning sequences (NaOH flush, water rinse, buffer equilibration) and temperature control (20–35 °C) ensure reproducible migration times (< 1 % RSD). Injection modes (hydrodynamic, stacking, electrokinetic) are selected to match analyte concentration ranges (ppb to ppm).

Main Results and Discussion

Across multiple application studies, CE achieved:

• Baseline separation of six to eleven ions within 5–10 min.
• Detection limits from 0.1 ppb (fluoride in H₂O₂) to 30 ppb (magnesium in yogurt).
• Linear quantitation over three orders of magnitude (10 nM to 250 µM) with r² > 0.98.
• Excellent precision: migration time RSD < 1 % and peak area RSD < 5 % for most analytes.

Key insights include selection of visualizing reagents (imidazole vs. p-aminopyridine) for cation matching, mobility-match stacking for concentrated samples, and helium or NaOH blanketing to protect redox-sensitive analytes (sulfide, sulfite).

Benefits and Practical Applications

CE on the Agilent 7100 system delivers:

• Lower cost per analysis due to inexpensive capillaries and minimal buffer use.
• High throughput with unattended buffer replenishment and rapid run-to-run cycle times.
• Flexibility to analyze cations, inorganic anions, organic acids and forensic toxins with a single platform.
• Robust performance in challenging matrices: dairy, wines, power plant effluents, semiconductor reagents and pulp mill liquors.

Future Trends and Potential Applications

Emerging directions include coupling CE to mass spectrometry for enhanced sensitivity and structural information, integration with microfluidic sample handling for point-of-use diagnostics, and expansion of indirect detection chemistries for neutral compounds. Further standardization through ASTM, SEMI and ISO guidelines will broaden CE adoption in regulated industries.

Conclusion

The Agilent 7100 CE system establishes CE as an indispensable tool for ion analysis across environmental, industrial and forensic laboratories. Its speed, sensitivity and low operating costs, combined with ready-to-use solution kits and standardized methods, enable reliable monitoring of ionic contaminants and process parameters in diverse applications.

References

• Ehmann T, Serwe M. Optimization of the Electrokinetic Sample Introduction in Capillary Electrophoresis for Ultra-Trace Anion Determination on Silicon Wafers. Chromatographia. 1997;45:301–311.
• SEMI Standard M33-0998. Test Method for Determination of Residual Surface Contamination on Wafers by Total Reflection X-Ray Fluorescence. SEMI; 1998.
• ASTM D5127-99. Standard Guide for Ultra Pure Water Used in Electronics and Semiconductor Industries. ASTM International; 1999.