Chemistry Reference
In-Depth Information
orthophosphate, pyrophosphate and tripolyphosphate (P
3
O
10
5−
) is shown.
Yaza
et al.
[238] used high performance liquid chromatography with a photodiode
array detector to analyse mixtures of polyphosphates, orthophosphates and
monofluorophosphates.
2.22.2
Ion exclusion chromatography
Ion exclusion chromatography provides a convenient way to separate molecular acids
from highly ionised substances. The separation column is packed with a cation exchange
resin in the H
+
form so that salts are converted to the corresponding acid. Ionised acids
pass rapidly through the column while molecular acids are held up to varying degrees. A
conductivity detector is commonly used.
Tanaka
et al.
[239-241] have reported that the separation of phosphate from chloride,
sulphate and several condensated phosphates P
2
O
7
4−
(pyrophosphate) and P
3
O
10
2−
and
P
3
O
10
3−
(tripolyphosphates) could be achieved by ion exclusion chromatography on a
cation exchange resin in the H
+
form by elution with an acetone:water and dioxan:water
mixture. As the separation mechanism of the ion exclusion chromatography by elution
with water alone for numerous anions or their respective acids is based on the Donnan
membrane equilibrium principle (ion exclusion effect), it is a highly useful technique for
the separation of non-electrolytes such as carbonic acid from electrolytes such as
hydrochloric acid and sulphuric acid [242]. Ion exclusion chromatography has also been
coupled to ion chromatography to determine simultaneously both weak and strong acids
[243]. The ion exclusion chromatography separation of orthophosphate from the strong
acid anions by elution with organic solvent-water described above is based on this ion
exclusion effect and/or the partition effect between the cation exchange resin phase
(water rich) and the mobile phase (organic solvent rich) owing to the hydration of the
resin [239] and phosphate has been monitored as the corresponding acid (H
3
PO
4
) with a
flow coulometric detector for the detection of H
+
ion and a conductometric detector.
The application of this technique is also discussed under multianion analysis in section
13.2.1.3.
2.23
Cyanide (free)
2.23.1
Spectrophotometric method
Williams [244] and others [245] have described an autoanalyser method for the
determination of 1-250µg L
−1
cyanide in non saline waters. In this method cyanide is
determined spectrophotometrically by means of the pyridine-pyrazolone method. The
extinction of the formed complex is measured at 620nm and is in relation to the
concentration of the cyanide. The cyanide is oxidised with chloramine-T. The formed
cyanogen chloride reacts with the pyridine-pyrazolone mixture to form a blue coloured
complex. The apparatus used is illustrated in Fig. 2.19.
Broderius [246] determined free cyanide and hydrocyanide in non saline waters and
industrial waters directly by bubbling compressed air
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