Anions in aqueous precipitation - Determination of Anions in Natural and Treated Waters - page 445

5.1.11.8 Gas chromatography
Faiqle and Klochow [32] applied gas chromatography to the determination of traces of
sulphate (and nitrate and phosphate) in rainwater. The dissolved salts are freeze dried and
converted to the corresponding silver salts. These are then converted to the n -butyl esters
with the aid of n -butyl iodide, the butyl esters being determined by gas chromatography.
Sulphate (and phosphate) are determined simultaneously on a column containing 3%OV-
17 on Chromasorb, while nitrate is determined separately with 3% of tri-p-cresol
phosphate on Chromasorb.
The application of this technique is also discussed under multianion analysis in section
14.1.2.1.
5.1.12 Sulphite
5.1.12.1 Ion chromatography
An ion chromatographic method for determining sulphite (and other ions) in rainwater
uses formaldehyde (0.02%) for sulphite preservation and a solution containing potassium
hydroxide and sodium carbonate as eluent [44]. The method has a linear range of 0-15mg
L −1 , a detection limit of 0.125mg L −1 and gives recoveries of 90-110%; relative standard
deviation was 1.5% for six measurements of sulphite at 12mg L −1 levels.
The application of this technique is also discussed under multianion analysis in section
12.4.1.
5.1.13 Thiocyanate
5.1.13.1 High performance liquid chromatography
The application of this technique is discussed under multianion analysis in section
13.1.3.1.
5.1.14 Multianion analysis
5.1.14.1 Continuous flow analysis: nitrate, nitrite, sulphate, chloride,
bromide and phosphate
A computer controlled multichannel continuous flow analysis system has been applied to
the measurement of sulphate (and nitrate, nitrate chloride, bromide and phosphate) in
small samples of rainwater [23,45,46]. Continuous flow methods (flow injection analysis
and continuous flow analysis have been used [22] to determine sulphate, chloride, nitrate,
nitrite and phosphate in rainwater. While the two methods are similar, they differ in
certain important respect, such as the rate of flow, presence of air bubbles, diameter of
the tubes and the reactions which are permissible within the retention period limits set by