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4.2 Design
Reference system lead (1) is immersed in the electrolyte and
provides a fixed reference potential for measurement as an Ag/AgCl
electrode, with the chloride ions contained in the electrolyte.
If the sample solution contains ammonia (NH
3
), for example, the
gas diffuses through the gas-permeable PTFE film (6) until the
partial pressure of the ammonia is the same on both sides of the
film (6). As the partial pressure changes, so does the pH value in the
thin layer of liquid upstream from the glass membrane (5). This
process is recorded by the hydrogen ion-sensitive glass membrane
(5). As the partial pressure depends on the concentration of
ammonia in the sample solution, the pH value can be used to
determine the ammonia concentration in the solution.
(1) Reference system lead
(2) Electrolyte
(3) Internal buffer
(4) Internal lead (Ag/AgCl)
(5) Glass membrane (hydrogen ion-
(6) Gas-permeable PTFE film
(Ag/AgCl)
selective) with a thin electrolyte layer