Anions in aqueous precipitation - Determination of Anions in Natural and Treated Waters - page 427

Chapter 5
Anions in aqueous precipitation
This chapter discusses the determination of anions in aqueous precipitation including
rain, snow, fog and aerosols.
Aqueous precipitation from the atmosphere occurs in many forms notably rain water,
dew, mists, snow, ice and hail. Anions, cations and indeed, organic substances can occur
in aqueous precipitation and measurements of these are of great interest in areas such as
acid rain studies, radioactive fallout from bomb tests and nuclear accidents and of course,
general pollution of the atmosphere, hence of the rivers and oceans. A growing volume of
measurements have been carried out in this field and these are discussed below under two
headings: rain water and snow/ice.
5.1 Rain
5.1.1 Bromate
5.1.1.1 Ion chromatography
The application of this technique is discussed under multianion analysis in section
5.1.14.3.
5.1.2 Bromide
5.1.2.1 Spectrofluorometric method
Fishman et al. [1] compared an automated fluorescein method and ion chromatography
for determination of bromide in rain water, and deionised water, at intervals over a period
of 30 d. The fluorescein method involved buffering the sample to pH 5.6, oxidation of
bromide to hypobromous acid with chloramine-T, and addition of fluorescein which
reacted with hypobromous acid to form tetrabromofluoresecin (eosin), the pink colour of
which indicated bromide ion concentration. The results obtained by the two methods
were not significantly different at a confidence level of 95% for samples containing
0.015-0.5mg bromide L −1 , and the correlation coefficient for the same sets of paired data
was 0.9987. There appeared to be no loss of bromide from solution during storage in
either polyethylene or polypropylene bottles. It was concluded that, where large numbers
of samples were to be analysed, the automated fluorescein technique would be the
method of choice, since it was more rapid than ion chromatography.