Easy-to-Make Capillary-Based Reference Electrodes with Controlled, Pressure-Driven Electrolyte Flow

Evan L. Anderson, Blair K Troudt, Philippe Bühlmann

Research output: Contribution to journalArticlepeer-review


As solid-contact potentiometric sensors based on novel materials have reached exceptional stabilities with drifts in the low μV/h range and long-term and calibration-free potentiometric measurements gain more and more attention, reference electrode designs that used to be satisfactory for most users do not satisfy the needs of new challenging applications. It is important that the interface between a reference electrode and the sample, often provided by a salt bridge, remains constant in ion composition over time. Excessive restriction of the flow of the bridge electrolyte, e.g., by using nanoporous frits or gelled reference electrolyte solutions, can result in contamination of the salt bridge with sample components and depletion of the reference electrolyte by diffusion into samples. This can be avoided by using salt bridges that flow freely into the sample. However, commonly used reference electrodes with free-flowing junctions often suffer either from experimental difficulties in assuring a minimum flow rate or from excessive flow rates that require frequent replenishing of the bridge electrolyte. To this end, we developed a reference electrode that contains a concentrated electrolyte contacting samples through a 10.2 μm capillary. By applying a minimal pressure of 10.0 kPa, a flow rate of 100 nL/h is achieved. This maintains a constant liquid junction potential at the interface with the sample and avoids contamination of the reference electrode, as evidenced by a potential stability of 6 ± 3 μV/h over 21 days. With such a minimal flow rate, there is no need to refill the reference electrode electrolyte for years.

Original languageEnglish (US)
Pages (from-to)2211-2217
Number of pages7
JournalACS Sensors
Issue number6
StatePublished - Jun 25 2021

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation (CHE-1710024). E.L.A. thankfully acknowledges the Lester C. and Joan M. Krogh Endowed Fellowship, an ACS Division of Analytical Chemistry and Eastman Summer Fellowship, and a Dissertation Fellowship from the Graduate School, University of Minnesota.

Publisher Copyright:
© 2021 American Chemical Society.


  • capillary
  • charge screening
  • liquid junction
  • potential stability
  • reference electrodes
  • salt bridges

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.


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