Pipet-based electrodes

Pipet-based electrodes have been used for a wide range of applications, e.g., micropipet ion-selective electrodes (ISEs) for potentiometric determination... 

The purpose of the reference barrel is to allow for the simultaneous measurement of the cell membrane potential while measuring the intracellular ion activities with the ISE portion of the device. Tims, in practice, a second single-barrel reference micropipet electrode is placed in the bathing solution outside the cell so that the potential between the two KCl-filled electrodes can always be monitored to obtain the instantaneous cell membrane potential (E ). The potential of the liquid membrane ISE barrel can also be monitored versus the external reference electrode. In this manner, potential changes due to variations in the cell membrane potential can be taken into account when calculating the intracellular ion activities. Alternatively, only the potential difference between both barrels of the electrode could be monitored. This potential should only be dependent on the intracellular activity of the analyte ion (not affected by the cell membrane potential). For certain ion measurements, e.g., K using a valinomycin based liquid micropipet electrode, leakage of K+ from the reference barrel could present a problem. In such cases, the reference barrel and the outer reference pipet should be filled with a solution other than 3 M KCl. 

A necessary step in conducting these measurements is preparation of the WE. A well-developed procedure for electrode preparation is described by Mayrhofer et al. [3]. A small amount of catalyst power (Pt- or Pt alloy-based catalyst) is first mixed ultrasonically with deionized water, followed by the addition of alcohol or isopropanol ( 1.0 ml alcohol to 5 mg catalyst) and 5 wt.% Nation ionomer solution (-1/40 volume ratio with the alcohol) to form a well-mixed catalyst ink. Then a small amount of catalyst ink is pipetted and coated onto a disk electrode surface such as GC or gold electrode, with a geometric area of 0.2-0.5 cm. The coated electrode is then left to air dry. The total catalyst loading on a GC electrode can be adjusted to 0.02-0.2 mg cm . ... 

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