BS 6068-2.50:1995 Water quality. Physical, chemical and biochemical methods - Determination of pH
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1.1 Field of application
This method is applicable to all types of water and
waste water samples in the range from pH 3 to
pH 10.
1.2 Interferences
The temperature, some gases and organic materials
interfere with the pH-measurement. Suspended ma-
terials in the sample may cause significant errors
(suspension effect). Wait for sedimentation and only
insert the electrodes in the clear fraction. Alterna-
tively, ultrafiltrate ca be taken. When measuring
sewage and some surface waters, there is a particu-
larly high risk of smearing the electrodes or contami-
nating the membranes and diaphragms with oil,
grease or other contaminants.
In the case of reference electrodes, this can be pre-
vented (see 5.4, note 2). If precipitation takes place in
the diaphragm, for example silver sulfide or protein
flocs, it will be necessary to form an electrolyte bridge
between the sample and the reference electrode with
inert electrolytes, e.g. c(KNO3) = 1 mol/l.
Regular cleaning of the electrodes is necessary (see
9.2).
