Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 301

solution and solid lead sulphate were derived and applied them to the potentiometric
determination of sulphate in solutions. With this procedure, a linear calibration graph can
be obtained from a plot of measured potential-related variables vs the concentration of
sulphate in solutions. Similarly, by following the same procedures, a standard addition
method can also be applied to the potentiometric determination of sulphate.
In this work, based on the behaviour of lead ion selective electrode and the interaction
between a sulphate-containing solution and solid lead sulphate, equations describing the
explicit linear relationships between the measured potential of lead in selective electrode
and the sulphate concentration in sample solutions were derived and applied to the
determination of sulphate by the flow injection analysis technique. These proposed
procedures improved the sensitivity of the potentiometric method and the reliability of
the analytical results. With a mixed solvent system (35 vol% methanol) a detection limit
as low as 1.0×10 −3 M can be obtained optimistically.
The application of this technique is discussed under multianion analysis in sections
14.4.1.1, 14.4.1.4 and 14.4.1.6.

2.93.7 Atomic absorption spectrometry
In an indirect flow photometric method [778], sulphate is precipitated in hydrochloric
acid medium by addition of a known amount of aqueous barium chloride, followed by
flame photometric determination of excess barium in the filtrate at 493nm. Atomic
absorption spectrophotometry has also been used to determine sulphate. Little et al. [779]
precipitated sulphate as lead sulphate from 40% ethanol medium and unconsumed lead
was determined by atomic absorption spectrometry. Siemer et al. [780] precipitated
sulphate as lead sulphate. The precipitate was filtered off on a porous graphite cup which
was then placed in a constant temperature Woodriff furnace for analysis of lead by non-
resonance line atomic absorption spectrometry. Calcium and chloride had no effect on the
determination but high phosphate levels enhance the lead signal. Non saline waters were
analysed by this method and results compared well with those obtained by turbidimetric
and gravimetric methods.
Montiel [781] reacted sulphate in a buffered medium with excess standard barium
chloride. Unreacted barium was then determined by atomic absorption spectrometry at
553.55µm and the concentration of sulphate in the sample calculated. Errors due to the
presence of alkali and alkaline earth metals are corrected by the incorporation of calcium
in the standard solution and by the presence of sodium in the buffer solution.
Kokkenonen et al. [782] have carried out the indirect determination of sulphate (and
sulphite) in non saline waters by flame atomic absorption spectrometry.
Englmaier [783] determined sulphate concentrations in non saline water by addition of
barium ions, centrifugation of the precipitate, and atomic absorption spectrophotometric
determination of the excess barium ions at 553.6nm, using cesium as a radiation buffer.
The method gave a detection limit of 0.0352mg of sulphate L −1 and a reproducibility of

1.5% at sulphate concentrations of 0.5-20mg L −1 .
A standard UK procedure [784] is based on the addition of excess barium chloride
solution to the sample and after precipitation of barium sulphate the excess barium is
determined using atomic absorption spectrometry with an air-acetylene flame. This