Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 132

Fig. 2.13 Flow system for the simultaneous determination of chloride and
sulphate. Sampling rate 200 samples h −1 . Tube length and i.d. are
given in cm and mm respectively
Source: Reproduced with permission from Elsevier Science [179]

a measure of the chloride concentration in the initial sample. Not surprisingly, many
anions interfere with this method when present in concentrations comparable to that of
the chloride.

2.17.3 Flow injection analysis
Van Staden [178] has described an automated prevalve dilution inflow injection analysis
method for the determination of chloride in ground water. This method can analyse
samples containing up to 800mg L −1 chloride. By adjusting the ratio of sample flow rate
to dilution water flow rate, the concentration could be reduced to a level at which
linearity of the calibration was preserved (about 160mg L −1 maximum). The method was
based on reaction with mercury thiocyanate in the presence of ferric ions, giving the
deeply coloured ferric thiocyanate. Absorption was measured at 480nm.

Table 2.8 Precision of the proposed FIA method for chloride in surface, ground and
domestic waters

Sample Number of
tests

Automated segmented
method [Cl − ] (mg L −1 )

FIA method
[Cl − ] (mg l −1 )

Coefficient of
variation (%)

1 15 8 11 1.21

2 15 66 74 0.87

3 15 7 10 1.05

4 15 239 251 0.21

5 15 26 26 0.99

6 15 107 110 0.74

7 15 149 150 0.66

8 15 6 4 1.30

9 15 239 245 0.15

10 15 7 5 1.14

11 15 26 30 0.91

12 15 302 291 0.17

Student's t -test at 5% probability level: calculated t -value=1.298; critical t -value=2.060
Source: Reproduced with permission from Elsevier Science [179]