Fabrication of microelectrodes for pH determination

Various pH microelectrodes and numerous fabrication techniques have been developed. Some selected examples of microelectrodes based on the formats of pH sensitive materials are discussed in this section. 

---

The results provided in the 1st PT campaign for pH, conductivity, Ca, K, Na and chloride were obtained by in-house fabricated microelectrodes (Chapter 4.1.4 of this book). The sensor used for pH determination is a pH-ISFET with silicone nitride membrane, the sensors for Na+, K+, Ca2+ and Cl- are ISFETs with ion-selective membranes, while the sensors for conductivity is a 4-bar platinum electrode. All the circuits used for measuring with the sensors (ISFET meter and conductivity meter) were also developed in-house. The results for the ions (Na+, K+, Ca2+ and Cl-) were received being expressed in activity, therefore could not be compared with the other PT results. 

Microelectrodes based on closed-end pH glass membranes were the first to be described in the literature (Cl). Hinke (H2) fiuther developed glass membrane microelectrodes with tip diameters of 10 im for the measurement of sodium and potassium. Various designs and approaches to the fiibri-cation of these all-glass microelectrodes have been taken over the years, and specific fabrication procedures may be found in the literature (H3, K3). Similarly, solid-state type electrodes based on pressed pellets of Ag2S with tip diameters on the order of 100 fim have been reported for the determination of Ag" ", S , I, Cl , Cu +, Br , etc. (C13). We have already discussed that such solid-state electrodes can foul when applied for direct measurements in biological systems, so the fabrication of these will not be discussed here. 

---