Introduction - Determination of Anions in Natural and Treated Waters - page 2

to various auxiliary functions, which can be freely programmed, up to four different
titrations can be performed on a single sample.
In addition to the fully automated 670 system, Metrohm also supply simpler units with
more limited facilities which nevertheless are suitable for more simple titrations. Thus the
model 682 titroprocessor is recommended for routine titrations with automatic
equivalence pointer cognition or to preset end points. The 686 titroprocessor is a lower-
cost version of the above instrument, again with automatic equivalence point recognition
and titration to preset end points.
Mettler produce two automatic titrators, the DL 40 GP memotitrator and the lower-cost
DL 20 compact titrator. Features available on the DL 40 GP include absolute and relative
end-point titrations, equivalence-point titrations, back-titration techniques, multi-method
applications, dual titration, pH stating, automatic learn titrations, automatic determination
of standard deviation and means, series titrations, correction to printer, acid balance
analogue output for recorder and correction to the laboratory information system. Up to
40 freely definable methods can be handled and up to 20 reagents held in store. Six
control principles can be invoked. The DL 20 can carry out absolute (not relative) end-
point titrations and equivalence-point titrations, back-titration, series titrations, and
correction to printer and balance and the laboratory information system. Only one freely
definable method is available. Four control principles can be invoked.
The DL 40 GP can handle potentiometric, voltammetric or photometric titrations.

1.1.2 Spectrophotometric method

1.1.2.1 Visible spectrometry

This technique is only of value when the identity of the compound to be determined is
known. There are also limitations on the sensitivity that can be achieved, usually
milligrams per litre or occasionally, micrograms per litre.
The following 35 anions have been determined by this technique in a variety of types
of water samples.

Non saline waters: arsenate, borate, bromide, chloride, chromate, dichromate, free cyanide,
dithionite, fluoride, iodate, nitrate, nitrite, phosphate, selenate, selenite,
silicate, sulphate, sulphide, sulphite, tellurate, thiocyanate, titanate, uranate
and vanadate, also ascorbate.

Sea water: alkalinity, arsenate, arsenite, borate, bromate, bromide, fluoride,

hypochlorite, iodate, iodide, nitrate, nitrite, phosphate, silicate and sulphate,

Estuary water: nitrate, nitrite and phosphate.

Aqueous
precipitation:

iodide, nitrate and sulphate.

Surface, ground
and porewaters:

borate, nitrate, nitrite, iodide, phosphate

Potable waters: alkalinity, bromide, fluoride, iodide, nitrate, nitrite, phosphate and sulphate.