Introduction - Determination of Anions in Natural and Treated Waters - page 81

(f) Formation of aluminium fluoride complex in a graphite furnace followed by molecular
absorption spectrometry at 227.45nm.
(g) Conversion of silicate to silicon tetrafluoride with hydrofluoric acid/ nitric acid and
analysis of silicon tetrafluoride solution by atomic absorption spectrometry.
(h) Indirect determination of sulphate by addition of excess barium chloride to form
barium sulphate, followed by determination of excess barium ions by atomic
absorption spectrometry.

Similar, and other, techniques have been employed for the determination of 10 anions
(sulphate, sulphide, bromide, chloride, fluoride, iodide, iodate, nitrite, nitrate and
tungstate) used in conjunction with an inductively coupled plasma atomic emission
spectrometric finish.

1.2.6 Electrochemical techniques

Electrochemical methods have been employed fairly extensively and include direct
polarography (18 anions), anodic scanning voltammetry (seven anions) and cathodic
scanning voltammetry (7 anions), amperometry (nitrate and nitrite), potentiometry (citrate
and iodide) and chronopotentiometry (chloride and cyanide). Between them these
techniques cover some 24 anions:

Polarography: arsenate, arsenite, bromide, chromate, citrate, iodate, iodide, nitrate,

nitrite, phosphate, selenate, selenite, silicate, sulphate, sulphide, sulphite,
bromate, perchlorate.

Anodic scanning
voltammetry:

bromide, phosphate, sulphate, chlorite, hypo-chlorite, polysulphide and
thiosulphate.

Cathodic scanning
voltammetry:

bromide, iodate, iodide, nitrate, nitrite, sulphide and chloride.

Amperometry:
Chrono-

nitrate and nitrite.

potentiometry: Chloride and cyanide.

Potentiometry: iodide and citrate.

In general, electrochemical methods offer the possibility of speciation of anions. Thus
arsenite and arsenate and selenate and selenite can be resolved. Ion selective electrodes
now have a reasonably larger number of applications, including borate, bromide, fluoride,
free and total cyanide, chlorite, iodate, nitrate, nitrite, sulphate, sulphide, sulphite and
thiocyanate.
Isotachoelectrophoresis is more limited in its range of applications which include
chlorite, hypochlorite, fluoride, nitrate, nitrite and sulphate.

1.2.7 Enzymic techniques
Enzymic assay methods have limited applications in the determination of anions