Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 137

a heat lamp. In the ion source the temperature of the ionisation filament is increased
stepwise up to a temperature of 1850°C.
Using sample amounts of 1µmol halide with natural isotope composition, ion
intensities are achieved on the Faraday cup in the range of 10 −11 to 10 −10 for 35 Cl − and in
the range of 10 −11 to 5×10 −11 for 79Br − .
Samples of 100-250g rain and snow were collected in polyethylene funnels of
diameter 35cm connected by means of polyethylene tubes and Y-brackets with a 1L
polyethylene flask. Approximately 100g of one sample was accurately weighed in a
250ml polyethylene beaker and approximately 1g 37 Cl spike solution was added. The
spike solution contained 1.014×10 19 chloride ions g −1 . Henman employed isotope
dilution analysis coupled with mass spectrometry to determine down to 13µg L −1
chloride in water [197].
The spike solution had an isotope distribution of 35 Cl=24.63% and 37 Cl =75.375%.
After the solutions of the spike and the sample had been stirred up and thoroughly mixed,
0.5ml of saturated silver nitrate solution was added and the mixture left to stand for about
30min so that the silver chloride could precipitate. After this, the solution was filtered
through a cellulose nitrate filter (Sartorius, Type 11301) and then, to purify it, the silver
chloride was dissolved again in some drops of a semiconcentrated ammonia solution. The
silver chloride was then precipitated again with concentrated nitric acid. After being
filtered, the precipitate was dried at 60°C and kept in a non-transparent flask until mass
spectrometry began. The silver chloride was kept away from light until measurement
because the chlorine isotopes fractionate slightly when silver chloride is decomposed by
light of a natural wavelength distribution. Shortly before the mass spectrometric
measurement was taken, 1 to 2 drops of a 15% ammonia solution were added to the
sample and placed on the evaporator filament of the thermal ion source of the mass
spectrometer using a micro-liter injector.
Henman et al. [197] determined chloride and bromide in snow and rain and also
measured their concentrations at different distances away from a highway (Table 2.10).
Unlike the concentrations of bromide, the chloride concentration in snow continually
decreases the further the snow is from the highway, a considerable proportion of the
bromide originating from traffic exhausts.
2.17.12 Radiochemical methods
Johannesson [199] treated the sample with H 35 Cl and evaporated it to dryness prior to
counting. He found that 1mg L −1 chloride could be determined.
In a radiometric determination of chloride in non saline water, excess mercuric ions are
added to the sample to form mercuric chloride complexes, followed by addition of a
chloroform solution of 60 Co-labelled Co-pyrrolidinedithiocarbamate complex [200]. The
excess mercuric ions displace an equivalent amount of cobalt from the dithiocarbamate
complex