Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 136

being analysed.
Chloride and fluoride determinations obtained in non saline water by this procedure are
compared with those obtained by conventional methods in Table 2.9. Generally, results
agreed within ±5% with those obtained by the reference method.
Trojanowicz and Matuszewski [193] investigated the usefulness of potentiometric
detection in the flow injection analysis of chloride in river waters. A direct, as opposed to
a logarithmic relation, exists between electrode potential and chloride concentration.
Hara et al. [194] found that preliminary treatment of river or stream water samples
with silver chloride was effective in removing interferences caused by bromide, iodide
and sulphide prior to potentiometric chloride determination using a chloride ion selective
electrode. The effects of pH on interference by bromide were also studied. Complete
removal of bromide interference was not possible by acidification of the sample alone.
Interference by humic substances in non saline waters in the ion selective electrode
determination of chloride was studied by Sikora and Stevenson [195]. The interference
was negligible in solutions containing less than 0.1g/L of humic substances but was
serious in samples with low concentrations of chloride (<10 −4.5 M) and high
concentrations of organic matter (0.1g L −1 ).
2.17.9 Vapour molecular absorption spectrometry
Zhang et al. [196] determined chloride in tap and lake water by vapour molecular
absorption spectrometry. Chloride was oxidised to chlorine by a strong oxidiser (eg
KMnO 4 ) in an acidic solution and the chlorine was introduced into a special cell of an
atomic absorption spectrometer, and the absorbance was measured at the wavelength of
the copper hollow cathode emission line of 324.7nm. The detection limit was 2.0mg L −1 .
2.17.10 Microwave induced helium plasma
Michlewicz and Carnahan have studied the application of this technique to the
determination of chloride in non saline water. In one method [186] the chloride is
converted to hydrogen chloride in a continuous flowing cell. The hydrogen chloride is
volatised into a microwave induced helium plasma and is determined by a microwave
technique which involves matrix matching.
In a further method [187] the aqueous sample is directly nebulised into an atmospheric
pressure helium microwave plasma.
2.17.11 Isotope dilution analysis
Henman et al. [197,198] employed mass spectrometric isotope dilution analysis to the
determination of chloride ion in rainfall and snow. Detection limits of 1µg L −1 or lower
can be achieved by this technique. For the isotope ratio measurement of chlorine and
bromide, a single focusing mass spectrometer (Varian MAT, type CH5TH) with a double
filament ion source and a Faraday cup as a detector was used. The filaments consist of
rhenium. The best precision of the isotope ratio measurement is achieved when a solution
of (Ag(NH 3 ) 2 ) X (X − =Cl − , Br − ) is deposited on the evaporation filament and dried under