Analytica Chimica Acta 526 (2004) 3–11 Screen-printed reference electrodes for potentiometric measurements Lukasz Tymecki a , El˙ zbieta Zwierkowska b , Robert Koncki a,∗ a Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland b Institute of Electronic Materials Technology, W´ olczy´ nska133, 01-919 Warsaw, Poland Received 3 August 2004; received in revised form 24 August 2004; accepted 24 August 2004 Abstract A convenient and reliable method for large-scale production of miniaturized, planar, all-solid-state reference electrodes is reported. All elements of the Ag/AgCl/KCl reference half-cell i.e. layer of Ag/AgCl (inner electrode), immobilized electrolyte (junction) and encapsulation are fabricated by means of screen-printing technology. The use of pastes cured in low temperature allows fabrication on low-cost, plastic, flexible foils. The developed reference electrodes exhibit good long-term stability. Continuous operation life-time exceeds one week. Storage stability is longer than 9 months. pH, chlorides as well as other halide anions, typical buffer components, alkaline and heavy metal cations, complexing ligands and redox agents, do not influence the potential of the reference electrodes. The developed reference electrodes are compatible with strip potentiometric sensors fabricated in the same format. Examples of analytical applications of the reference electrodes with various screen-printed sensors are demonstrated. © 2004 Elsevier B.V. All rights reserved. Keywords: Potentiometry; Reference electrode; Screen-printing; Thick film 1. Introduction Potentiometry is an attractive tool for many practical ap- plications as it allows determination of wide spectrum of ions and because it applies portable and inexpensive equipment. This analytical technique is especially useful for various med- ical and environmental tests carried at remote sites (‘in field’ measurements). Low-cost and small-size disposable elec- trode systems are desirable for these applications. Thin- and thick-film technologies are most suitable for production of the disposable sensors. Screen-printing is especially suitable due to its simplicity, low-cost, high reproducibility and efficiency in large-scale production. Several potentiometric sensors, in- cluding pH-electrodes based on metal oxides [1–3] and ze- olites [4], as well as various ion-selective electrodes based on liquid [5–7] and solid [8–10] membranes have been fab- ricated using screen-printing. Only recently, totally screen- printed urea enzyme electrode has been developed [11]. ∗ Corresponding author. Fax: +48 22 8225 996. E-mail address: rkoncki@chem.uw.edu.pl (R. Koncki). A reference electrode is necessary to complete electro- chemical cell. Lack of compatible, well-working reference electrode hinders utilizing disposable sensors. Although a lot of papers report on various electrochemical microsensors, only a few of them deal with microfabrication of planar ref- erence electrodes. Desmond et al. [12] have developed micro pseudoreference electrode by combining silicon and screen- printing technology: Ag/AgCl film was screen-printed onto platinum layer deposited on an oxidized silicon substrate. The achieved silver/silver chloride pseudoreference electrode was manually modified by casting a resin containing pow- dered KCl and some additives required for polymerization. Curing process was carried out for about 24 h. Another dis- posable reference electrode was developed using double ma- trix membrane technology [13]. Conducting Ag/AgCl film was screen-printed on heat-sealing paper, covered with filter paper and laminated together with the second sheet of the heat-sealing film. The filter paper, playing the role of support for KCl, was spontaneously filled with the electrolyte solu- tion by capillary forces. A micro-machined liquid-junction Ag/AgCl electrode, reported by Suzuki et al. [14], is based 0003-2670/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2004.08.056