Anions in estuary and coastal waters - Determination of Anions in Natural and Treated Waters - page 422

Chapter 4
Anions in estuary and coastal waters
Very limited work has been published on the determination of anions in estuary and
coastal waters. However, there is no doubt that the open seawater analysis methods
discussed in Chapter 3 would in many instances be applicable to estuary and coastal
waters.
4.1 Nitrate
4.1.1 Ultraviolet spectroscopy
Brown and Bellinger [1] have proposed an ultraviolet technique which is applicable to
both polluted and unpolluted fresh waters and some estuarine waters. Humic acid and
other organics are removed on an ion exchange resin. Bromide interference in seawater
samples can be minimised by suitable dilution of the sample but this raises the lower
limit of detection such that only on relatively rich (0.5mg L− 5 nitrate) estuarine and
inshore waters could the method be used. Chloride at concentrations in excess of
10,000mg L −1 does not interfere.
The method is either not affected by or can allow for interference from phosphate,
sulphate, carbonate, bicarbonate, nitrite, coloured metal complexes, ammonia, dyes,
detergents, phenols and other ultraviolet absorbing substances.
The determination of nitrite is also discussed under multianion analysis in section
4.6.1.
4.2 Nitrate and nitrite
4.2.1 Autoanalyser method
Petts [2] has described a procedure for the determination of total nitrate plus nitrite in
estuary waters ranging in salinity from 2.17 to 33.1g kg −1 . In this method oxidised
nitrogen in the sample is reduced to nitrite by a copper/cadmium reduction column, and
the total nitrite in the sample is then reacted with sulphanilamide and N-1-
naphthylethylene diamine dihydrochloride under acidic conditions to produce an azo dye
which is evaluated spectrophotometrically at 550nm. The range of application of the
method is 1-800µg NL −1 . Standard deviations range from 0.42µg NL −1 at the 14µg NL -1
level to 2.8µg NL −1 at the 70µg NL −1 level.