Certain substances which meet the criteria of (i) preparation in highly pure state
reproducibly and (ii) stability of solution over a reasonable period of time are designated
as operational standards in aqueous solution of specified concentration. Their number
is in principle unlimited but values are available now for 15 solutions. The values
of operational
pH standard, i.e.
,
are assigned by comparison with the
reference value pH standard, i.e.
,
in cells with
liquid junction, the operational cells, where the liquid junctions are formed within vertical
tubes.
Source:
