Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 92

16 113 117 108 0.55

17 96 98 95 0.30

18 138 142 132 0.22

19 178 201 187 0.28

20 183 204 199 0.35

21 174 194 193 0.21

22 174 196 186 0.48

23 167 186 178 0.21

24 65 68 66 0.30

25 30 28 26 1.10

*15 tests were carried out on each sample
Source: Reproduced with permission from United Trades Press [22]

2.9 Borate

2.9.1 Spectrophotometric methods

Choi and Chen [27] have developed a curcumin method using a 20% v/v 2-ethyl-1,3-
hexanediol, a boron complexing agent, in methyl isobutyl ketone as an extracting solvent.
A 5cm cylindrical quartz cell is used to measure absorbance against 100% ethyl alcohol
at a wavelength of 550nm. This method eliminates inconvenient time-limits and the
interference of fluorides, or nitrates. Using a 5cm cylindrical cell, the detectable range of
boron is approximately 0.25-3.0 mg L −1 with less than 5% error.
There is no significant interference from magnesium, calcium, and fluoride and nitrate
ions in this method. The detection limit of this method is approximately 0.2 mg L −1
borate.
In this method 1ml of water sample is transferred into a 10ml polypropylene tube
(17×100mm) with a friction-fit closure. 2ml of 1 N hydrochloric acid and 3 ml of 20 vol
% 2-ethyl-1,3-hexanediol in methyl isobutyl ketone is added and the solution shaken
vigorously for 2min. 1ml aliquot from the upper organic solvent layer of the extract is
transferred into a 50ml polypropylene centrifuge tube with a screw cap. 2ml of curcumin
reagent (0.375g 100 mL −1 glacial acetic acid) is added and then 0.5ml of concentrated
sulphuric acid. The centrifuge tube is closed immediately after the addition of
concentrated sulphuric acid and the bottle swirled until the yellowish colour turns to a
dark purple colour. The reaction may be terminated at any time under 23h by adding 50
ml of 100% ethyl alcohol. The absorbance of the solution is measured against 100% ethyl
alcohol at a wavelength 550nm with a 5cm cylindrical quartz cell (glass and quartz
function equally well in the visible portion of the spectrum). The absorbance of the
solution can be measured 60min after the addition of alcohol. The time span between the
addition of alcohol and the measurement of absorbance can be arranged according to the