The electrode comes with a cap and the minimum volume that is required is the amount to cover the Platinum tip. This is around 0.5 ml but to be safe a 1 ml solution should be more than adequate. The electrode obeys the Nernst equation if the redox couple is reversible on the platinum surface. Most common oxidizing agents such as chlorine, ozone etc do not behave reversibly on platinum, so the relationship between concentration and mV output is not linear and has to be experimentally determined. In this case you need a number of concentrations to define the curve. In a Nernstian case, you do not need a multipoint calibration as in a pH electrode because the output is a function of the ratio of the oxidized to reduced species. The IJ64 instruction manual covers some of this.
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