Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 302

method is capable of determining down to 5mg L −1 sulphate with a standard deviation
ranging from 1.2mg L −1 at the 20mg L −1 sulphate level to 1.6mg L −1 at the 175mg L −1
sulphate level.
2.93.8 Inductively coupled plasma atomic emission spectrometry
Inductively coupled plasma atomic emission spectrometry has also bee used to determine
sulphate directly in non saline waters [785].
By monitoring the 180.73nm sulphur line, it was possible to detect 0.08mg L −1
sulphate with a precision of 0.8% RID at the 200mg L −1 sulphate level.
Cox et al. [786] have developed a rapid and sensitive method for determining sulphate
in non saline waters based on flow injection inductively coupled plasma atomic emission
spectrometry. A microcolumn of activated alumina in the acidic form was used in the
flow injection manifold to preconcentrate sulphate before inductively coupled plasma
atomic emission spectrometry determination at 180.73nm. The calibration curve was
linear over the concentration range of 0-1000µg L −1 , and the limit of detection (based on
2mL sampling volumes) was 2.8µg L −1 . Relative standard deviation at 10 and 1000µg
L −1 were 7.0 and 0.8% respectively.
2.93.9 Capillary coupling isotachoelectrophoresis
Bocek et al. [787] determined sulphate (and chloride) in mineral waters by this technique
and Zelinski et al. [788] applied the technique to the determination of 0.02 to 0.1mg L −1
quantities of sulphate, chloride, fluoride, nitrate, nitrite and phosphate in river waters.
The application of this technique is discussed under multianion analysis in section
14.6.1.1.
2.93.10 Ion selective electrodes
In an indirect method [789], excess ferric ions are added to the sample to complex the
sulphate. The solution is then titrated with barium chloride and liberated ferric iron
detected with an iron-selective electrode. In another method [762], sulphate is titrated
directly with 0.01mol L −1 lead perchlorate in the presence of 50% dioxan, the end-point
being detected with a lead-selective electrode. The indirect method is subject to several
interference effects. The direct method is subject to interference effects by metal ions and
phosphate. Hulanicki et al. [790] eliminated ionic inter-ferences in the determination of
sulphates using a lead sensitised ion selective electrode. Jones et al. [791] studied
interferences of a barium ion selective electrode used in the potentiometric titration of
sulphate.
Hara et al. [767] have applied a continuous flow method using a lead-selective
electrode for the determination of sulphate.
A solid state lead selective electrode has been used to estimate sulphate in mineral
waters [792]. The sample is passed through two columns of strong cation-exchange
resins, the first in the Ag + form (to remove chloride) and the second in the H + form (to
remove bicarbonate). After adjustment of the pH of the effluent to between 5 and 6,