Anions in potable waters - Determination of Anions in Natural and Treated Waters - page 498

Braintree 13.7 13.9

Benson 5.8 6.5

London (borehole) 28.0 30.0

File 7.8 5.8

Nottingham 14.0 15.4

Dunoon 1.1 1.1

London (tap) 5.8 5.9

Source: Reproduced with permission from the Royal Society of Chemistry [38]

Grandet et al. [12] have described a gas chromatographic method for the determination
of µg levels of iodide in potable water.
The application of this technique is discussed under multianion analysis in section
7.28.3.

7.17 Molybdate

7.17.1 Preconcentrati/on
The preconcentration of molybdate is discussed in section 15.2.1.

7.18 Nitrate

Groundwaters provide almost 40% of the domestic water supply in England and Wales
and the concentration of nitrate present has an important bearing on potability. The
current WHO standard for European drinking water [41] recommends that levels of
nitrate should not exceed 11.3mg L −1 of nitrate-nitrogen (50mg L −1 of nitrate). High
levels of nitrate can give rise to harmful physiological effects, such as
methaemoglobinaemia, particularly in infants, and at present there is concern over
evidence that suggests that nitrate concentrations in some major aquifers are increasing to
an undesirably high level. Analytical methods for nitrate therefore need to be accurate so
that threshold values can be determined with confidence, and precise so that small trends
in concentration can be detected quickly.

7.18.1 Spectrophotometric methods

Spectrophotometric methods employing brucine [42] and Devarda's alloy reduction to
ammonia followed by Nesslerisation [43] and the use of dihydroxycoumarin [44] have all
been employed for the determination of nitrate in water. Apart possibly, from the
dihydroxycoumarin [44] method, which employs an ethyl acetate extraction step, none of
these methods is sufficiently sensitive for the determination of nitrate in potable water.