Anions in aqueous precipitation - Determination of Anions in Natural and Treated Waters - page 435

interferes at the 1:100 level and above, and nitrite interferes slightly at the 1:10 level and
above. These two interferents can be removed, however, by the addition of silver sulphate
or mercury sulphate and sulphamic acid, respectively, to the sample solution prior to
extraction with toluene.
5.1.7.2 Continuous flow analysis
This technique has been applied to the determination of nitrate in rainwater [22] (and
chloride, nitrite, phosphate and sulphate).
A computer-controlled multichannel continuous flow analysis system has been applied
to the measurement of nitrate (and chloride) in small samples of rainwater [23].
The application of this technique is discussed under multianion analysis in section
5.1.14.1.
5.1.7.3 Flow injection analysis
Madsen [24] used flow injection analysis with hydrazine reduction and
spectrophotometric detection at 540nm to determine less than 1mg L −1 nitrate in rain
water. Forty samples per h can be analysed with a precision of 30% in the range 1-10mg
L −1 .
The application of this technique is discussed under multianion analysis in sections
5.1.14.4 and 14.4.2.1.
5.1.7.4 Electrochemical methods
Electrochemical methods that have been used to determine nitrate include polarography
[25,26]. Bodini and Sawyer [27] described a voltammetric determination of nitrate at the
µg L −1 level. This electrocatalytic method utilises the concomitant reduction of cupric
chloride and cadmium chloride on pyrolytic graphite to catalyse the reduction of nitrate
ion.
5.1.7.5 Capillary isotachoelectrophoresis
Kamiansky et al. [28] determined nitrate and sulphate in rain water by capillary
isotachophoresis. Separation conditions were chosen to eliminate potential interference
from formate, acetate and propionate. Sulphate and nitrate were separated at pH 6.0 using
histidine or 1, 3-bis (tris(hydroxymethyl)methyl)aminopropane as buffering agents. The
complex forming cations, magnesium and calcium, were also suitable for optimising
separating conditions. Sulphate was retarded, relative to nitrate, by using trimethylene-
tetramine as a co-counter ion in the leading electrolyte.
5.1.7.6 Mass spectrometry
Ligon and Dorn [29] determined nitrate and sulphate in rain by mass spectrometry.