Chemistry Reference
In-Depth Information
and double function. Indicating or sensing electrodes are of four types:
• solid state
determination of Br
1−
, Cd
2+
, Cl
1−
, Cu
2+
, CN
1−
, F
1−
. I
1−
. Pb
2+
, Redox,
silver/sulphide
1−
, Na
+
, CNS
1−
Ca
2+
, divalent (hardness), fluoroborate, NO
3
1−
, K
1+
, ClO
4
1−
, HF, surfactants
• liquid
membrane
• residual
chlorine
• glass sodium
Applications of ion selective electrodes to the determination of 16 anions in various types
of water are listed below.
Non saline waters:
sulphate, sulphite, thiocyanate, iodate, iodide, nitrate, nitrite and palmitate,
bromate, bromide, chloride, free cyanide, total cyanide and fluoride.
Seawater:
bromide, chloride and fluoride.
Aqueous
precipitation:
fluoride and sulphate.
Surface and ground
waters:
free cyanide and nitrate.
Potable waters:
fluoride.
Waste waters:
chloride, sulphate, sulphide, free cyanide, total cyanide, nitrate.
Sewage effluents:
chloride, nitrate and sulphide.
Trade effluents:
sulphate, sulphide and thiocyanate.
High purity water:
chloride.
Variables which effect precise measurement by ion selective electrodes are the following:
• concentration range
• ionic strength—an ionic strength adjuster is added to the samples and standards to
minimise differences in ionic strength
• temperature
• pH
• stirring
• interferences
• complexation
Traditionally electrodes have been used in two basic ways, direct poten-tiometry and
potentiometric titration. Direct potentiometry is usually used for pH measurement and for
measurement of ions like sodium, fluoride, nitrate and ammonium, for which good
selective electrodes exist.
Direct potentiometry is usually done by manually preparing ionic activity standards
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