Anions in potable waters - Determination of Anions in Natural and Treated Waters - page 517

Table 7.19 Comparison of results of sulphate determinations with three different methods

Sulphate ion (mg L −1 )

Sample
no

Gravimetric
n=1

Atomic absorption spectrometry n=5
(±1s)

Turbidimetric
n=2

10000-1 926 1077 (±31) 1180, 1168

6891-1 2800 2640 (±87) 2897, 2885

7036-1 52 57 (±4) 62.4, 60.5

7062-1 40 32 (±2.7) 29.0, 28.0

Source: Reproduced with permission from the Society for Applied Spectroscopy [85]

directed at precipitation of the sulphate with a metal ion followed by determination of the
metal retained on a porous graphite filter after washing off excess precipitant. Siemer et
al. [85] discovered that non-resonance atomic absorption at 405.7nm of the lead in a lead
sulphate precipitate served the purpose.
At a furnace temperature of 1550°C lead sulphate gives reasonable absorbance values
for the amounts of sulphate in potable water. From 50 to 75% of ethyl alcohol was
incorporated during the lead sulphate precipitation and washing steps to decrease
solubility errors. An excess of lead ions was added to the sample in this medium and
excess lead ions determined.
In Table 7.19 sulphate determinations obtained by this technique are compared with
those obtained turbidmetrically and gravimetrically.

7.25.6 Ion selective electrodes
Sun et al. [86] measured sulphate in mineral and drinking waters using a selective
electrode potentiometric titration method. They reported a detection limit of 5×10 −5 M
and relative standard deviations ≤ 3.7%.

7.25.7 Ion chromatography
Various workers [67,68,69,87-93] have discussed the application of this technique to the
determination of sulphate (Table 7.20).
The application of this technique is discussed under multianion analysis in sections
7.28.2, 12.6.1, 12.6.2 and 12.6.3.