Potentiometric Solid-Contact K⁺ Ion-Selective Electrodes Based on the KMnFe(CN)₆ Transducer

Area of Science:

• Electroanalytical Chemistry
• Materials Science
• Sensor Technology

Background:

• Traditional solid-contact ion-selective electrodes (SC-ISEs) rely on ion-selective membranes (ISMs), which are prone to water-layer formation and mechanical instability.
• These limitations hinder the long-term performance and reliability of conventional SC-ISEs.

Purpose of the Study:

• To develop an ion-selective membrane-free potassium ion selective electrode (K+-SC-ISE).
• To utilize a Prussian blue analogue, KMnFe(CN)6, as a bifunctional transducer for selective K+ recognition and ion-to-electron transduction.
• To address the challenges of water-layer formation and poor mechanical stability associated with conventional ISMs.

Main Methods:

• Synthesis of KMnFe(CN)6 via a one-step citrate-assisted co-precipitation method.
• Fabrication of a K+-SC-ISE utilizing the synthesized KMnFe(CN)6 as the sole active layer.
• Electrochemical characterization including potentiometric response, selectivity, and stability measurements.
• Validation using real lake water samples and comparison with ion chromatography.

Main Results:

• The KMnFe(CN)6-based sensor demonstrated a near-Nernstian response (52.3 ± 1.0 mV dec−1) with a rapid response time (25 s).
• Achieved a linear detection range from 10−4 to 10−1 M with a limit of detection of 5.8 × 10−5 M.
• Exhibited excellent selectivity against common interfering ions (log Ki,j values ranging from -0.95 to -3.06).
• Showcased remarkable long-term stability, avoiding the water-layer effect with a potential drift of 57.2 ± 6.1 μV h−1 over 7 days.
• Accurate K+ determination in real lake water samples, correlating well with ion chromatography data.

Conclusions:

• The development of an ion-selective membrane-free K+-SC-ISE based on KMnFe(CN)6 is successfully demonstrated.
• This approach effectively eliminates the water-layer effect, leading to enhanced sensor stability and reliability.
• The KMnFe(CN)6 transducer offers a promising strategy for developing robust and efficient electrochemical sensors for ion analysis in aqueous environments.