VODIVOSTNI VLÁKNOVÝ DETEKTOR PRO KAPILÁRNÍ ELEKTROFORÉZU

Importance of the Topic

Capillary Zone Electrophoresis (CZE) offers high separation efficiency, rapid analysis and minimal sample and solvent consumption. Conductometric detection extends CZE to inorganic ions that are difficult to monitor by UV methods. A major challenge is eliminating interference from the strong separation field on the conductivity measurement.

Objectives and Study Overview

This work presents a novel fiber-based conductometric detector for capillaries with internal diameters above 75 μm. The detector measures the conductivity of the eluting electrolyte on a hydrophilic cellophane strip attached at the capillary outlet. Performance was evaluated through determination of sodium and potassium ions in commercially available mineral waters.

Methodology and Instrumentation

• Instrument: CRYSTAL 310 CE system with integrated data acquisition (ATI Unicam, UK).
• Separation capillary: fused silica, 75 μm ID, 375 μm OD, 79 cm length, polyimide coating.
• Detector assembly: 10 mm×0.15 mm cellophane fiber glued with silver conductive epoxy to a tinned copper wire; fiber end positioned at capillary outlet; auxiliary platinum electrode immersed in buffer vial.
• Operating conditions: buffer 30 mM MES + 15 mM LiOH (pH 6.1); 20 kV separation voltage; 12 μA current; hydrodynamic injection at 20 mbar for 6 s.

Main Results and Discussion

• Calibration curves for K+ and Na+ were linear in the range 5×10⁻³ to 1×10⁻² mol·dm⁻³ with high precision.
• Comparison with indirect UV detection showed a ~10 % decrease in separation efficiency, attributed to the larger detection volume of the fiber cell.
• Analysis of Mattoni, Korunní and Mlýnský pramen mineral waters yielded concentrations in close agreement with label claims.

Benefits and Practical Applications

The detector design is simple, requires no specialized materials or complex field isolators, and is easily mounted on standard capillaries (>70 μm ID). It enables routine on-capillary conductometric detection of small inorganic ions.

Future Trends and Potential Applications

Advances may include use of alternative hydrophilic fibers or coatings to boost sensitivity, integration with microfluidic and portable CE platforms for field analysis, and extension to other ionic analytes and complex sample matrices.

Conclusion

The fiber-based conductometric detector effectively suppresses separation field interference, exhibits linear response to analyte concentration, and minimally impacts separation efficiency. Its straightforward construction and adaptability make it valuable for routine CZE applications in environmental and industrial analysis.

Used Instrumentation

• CRYSTAL 310 CE instrument (ATI Unicam, UK)
• Unicam 4225 UV detector for comparative indirect UV measurements
• Cellophane fiber, silver conductive epoxy (EPO-TEK H31D), copper and platinum electrodes

References

• Li S. F. Y.: Capillary Electrophoresis — Principles, Practice and Applications. Elsevier, Amsterdam 1992.
• Ewing A. G., Mesaros J. M., Gavin P. F.: Anal. Chem. 66, 527A (1994).
• Jandik P., Bonn G.: Capillary Electrophoresis of Small Molecules and Ions. VCH, Linz 1993.