pH sensors

are designed as single-use versions and are based on the optical and potentiometric measuring principle ²⁰. The optical determination of pH can be based on fluorescence or absorption, whereby fluorescence-based dyes such as fluorescence derivates or absorbing substances like phenol red are applied. The dyes are pH sensitive and show a pH value-dependent fluorescence or absorption in the solution. The advantage of optical pH sensors lies in their miniaturizability. However, the dyes can lose their sensitivity and are applicable only in a limited pH range of around 3 units. Potentiometric pH sensors measure the potentiometric deviation between the working and the reference electrode ⁴¹. They are also miniaturizable. Today, it is not yet possible to achieve comparably exact measurements as with conventional pH probes ⁶². See sensors, instrumentation.