Analytical · Glossary

What is Nernst Slope?

mV per pHAnalytical

Nernst slope is the theoretical change in electrode voltage per pH unit, 59.16 mV at 25 °C, rising with temperature.

Nernst Slope Explained

Calibration with two buffers measures the actual slope and offset. Slope is often reported as a % of theoretical.

Low slope means a tired or coated electrode; many sites accept roughly 90 to 105 % and an offset within about ± 30 mV, per their procedure.

S = 0.1984 × T mV/pH and Slope % = S_measured ÷ S × 100

T	temperature (K)

Example: pH 7 at −5 mV, pH 4 at +165 mV: 56.7 mV/pH, about 96 % at 25 °C, offset −5 mV.

What is Nernst Slope?

Nernst slope is the theoretical change in electrode voltage per pH unit, 59.16 mV at 25 °C, rising with temperature.

Why is the voltage negative at high pH?

By convention the electrode gives positive mV in acid and negative in alkali, about 0 mV at pH 7.

What is the isopotential point?

The pH where electrode voltage does not change with temperature, ideally pH 7.

Electrical conductivity explained

A practical guide on instrumentationblog.in with more detail on nernst slope and how it is applied on real plants.

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