Measuring ionic conductivity using screen-printing technology

Significance of the topic

Conductivity is a fundamental parameter for assessing aqueous samples because it reports the ionic content, correlates with salinity, and is a rapid indicator of contamination or dissolved solids. Reliable conductivity measurement is essential in water quality monitoring, industrial process control, and environmental screening. Minimizing sample volume and cross-contamination while preserving accuracy is increasingly important for decentralized and on-site testing.

Objectives and overview of the study

This Application Note demonstrates a disposable screen-printed electrode (11COND SPE) workflow to measure ionic conductivity (σ) of potable waters using only 100 μL sample volumes. The study compares results from the 11COND SPE against a conventional conductivity probe across eight drinking water samples (tap water + seven commercial bottled waters) to evaluate suitability, reproducibility, and practical advantages of the SPE approach.

Methodology

Measurements use electrochemical impedance spectroscopy (EIS) at a single high frequency (10 kHz) to capture the impedance magnitude (|Z|) where resistive (ohmic) behavior dominates. Key experimental conditions and steps:

• Temperature controlled and equilibrated at 25 °C.
• Place 100 μL of sample onto the SPE to cover both carbon contact areas.
• Measure |Z| (ohm) at open-circuit potential (OCP) and 10 kHz using an EIS-enabled potentiostat.
• Correct raw |Z| by subtracting the SPE internal/basal resistance r0 (provided on the SPE label).
• Convert corrected resistance to conductivity (see calculation below) using the SPE cell constant (Kcell) supplied with the electrode.

Calculation used in practice (units): conductivity σ (μS·cm^-1) = (1 / (|Z| - r0)) × 1,000,000 × Kcell.
Example provided: |Z| = 3638 Ω, r0 = 100 Ω → 1/(3638-100)×1e6 = 283 μS; with Kcell = 5 cm^-1 → σ = 1,413 μS·cm^-1.

Used instrumentation

• 11COND screen-printed electrode (SPE) — disposable carbon-based two-electrode ceramic strip; Kcell and r0 printed on the SPE box; operational conductivity range ~84 μS·cm^-1 to 111.8 mS·cm^-1.
• µStat-i M8One multi-channel potentiostat with EIS capability — enabled simultaneous EIS runs for multiple samples.
• DropView 8400M software — configured for single-frequency EIS (10 kHz) acquisition at OCP.
• Standard laboratory conductivity probe used as reference comparator.

Main results and discussion

The 11COND SPE produced conductivity values that closely matched those from the standard conductivity probe across all eight potable water samples. Each sample was measured with three independent SPEs to assess reproducibility; inter-electrode variability was low and error bars overlapped with the reference probe results. The data demonstrate that single-frequency EIS using the SPE reliably captures the solution resistance needed to compute conductivity, provided temperature, r0, and Kcell are properly accounted for. The method is particularly suitable for moderately concentrated aqueous media within the SPE specified range.

Benefits and practical applications

• Microvolume capability: only 100 μL required, enabling tests on scarce or precious samples.
• Disposable format reduces cross-contamination risk and removes probe fouling or mechanical damage concerns associated with conventional probes.
• Parallel measurements possible with multi-channel potentiostats for higher throughput.
• Applicable for decentralized, in-situ, and field screening where portability and small sample volumes are advantageous.

Limitations and operational considerations

• Measurements must be performed at controlled temperature (25 °C) for the formula and Kcell to be strictly valid.
• The SPE has a defined conductivity working range (84 μS·cm^-1 to 111.8 mS·cm^-1); values outside this range may not be accurate.
• Accurate use requires knowledge of the SPE-specific r0 and Kcell values printed on each electrode box and careful pipetting to fully cover the electrode area.

Future trends and potential applications

The combination of screen-printed sensor platforms with compact multi-channel EIS analyzers supports several future directions:

• Integration into portable, automated field kits for environmental monitoring and rapid contamination screening.
• Expanded SPE designs and materials to widen the measurable conductivity range and chemical robustness.
• On-device calibration strategies and temperature compensation algorithms to relax the strict 25 °C requirement.
• Coupling conductivity micro-measurements with other on-strip sensors (pH, ions, redox) for multifunctional water-quality test strips.

Conclusion

The 11COND screen-printed electrode, used with an EIS-capable potentiostat at 10 kHz and 25 °C, provides a reliable, reproducible, and low-volume method for measuring ionic conductivity in potable waters. Results were nearly indistinguishable from a conventional conductivity probe while offering practical advantages of disposability and microvolume operation. This approach is well suited for decentralized testing and scenarios where sample volume and contamination risk are limiting factors.

References

1. Baird RB, Rice EW, Eaton AD. Standard Methods for the Examination of Water and Wastewater, 23rd Edition. American Public Health Association; Washington, DC.
2. Lazanas AC, Prodromidis MI. Electrochemical Impedance Spectroscopy — A Tutorial. ACS Measurement Science Au 2023, 3 (3), 162–193.