Chemistry Reference
In-Depth Information
2.29
Dodecane sulphate
2.29.1
Ion chromatography
The application of this technique is discussed under multianion analysis in section 12.2.4.
2.30
Dodecane sulphonate
2.30.1
Ion chromatography
The application of this technique is discussed under multianion analysis in section 12.2.4.
2.31
Fluoride
2.31.1
Spectrophotometric methods
Anosova [294] determined fluoride in highly demineralised water by separating fluoride
ion as hydrofluoric acid by stream distillation of the sample (concentrated by evaporation
and treated with silver nitrate solution to precipitate fluoride ion) from sulphuric acid
medium. The distillate is treated with Alizarin red S (CI Mordant Red 3) solution,
buffered at pH 2.5-3.5, and then allowed to react with a known volume of standard
thorium nitrate solution. After 30min, the colour is compared with those of a series of
standards covering the range 0.0-0.1mg L
−1
fluoride.
Moraru and Suten [295] have reviewed Spectrophotometric methods for the
determination of fluorides. The methods have been described based on the use of
zirconium-xylenol orange [296], lanthanum-alizarin [297], and zirconium solochrome
cyanine R [298]. These methods are all capable of determining fluoride in µg quantities
in water samples. In an extractive Spectrophotometric determination of micro and
submicro amounts (down to 50µg L
−1
) of fluoride [299], buffered alizarin complex is
added to the sample which is then extracted with triethylaminepentanol (1:19) prior to
Spectrophotometric evaluation of the organic phase at 570nm.
A method for the determination of fluoride is based on the bleaching effect of fluoride
on a column of the zirconium eriochrome organic R complex [300]. This method is
applicable over the range 2-25µg fluoride. Sulphate does not interfere in the
determination. Lanthanum-alizarin complexone has been used to determine fluoride
[301]. The main interfering ions are removed from the sample with a strongly acidic
cation exchanger. The reagent (a buffered pH 4.3 mixture of 3-aminomethylalizarin-NN-
diacetic acid and lanthanum nitrate with added acetone) is added, and the red chelate is
allowed to develop in the dark for about 20min and the extinction determined against a
reagent blank at 620nm. If very high sulphate and chloride concentrations are present in
the sample, the results must be corrected by reference to a calibration graph. Water
samples containing aluminium (greater than 0.1mg L
−1
) must be adjusted to pH 9 with
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