Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 265

Fig. 2.39 Absorption spectrum of molybdophosphoric acid
Source: Reproduced with permission from Springer Verlag [651]
The corresponding silicon compound is not extracted into this solvent. Thus, the
interference by silicon is excluded even at concentrations as high as 10mg L −1 . A
wavelength of 251nm at the ultraviolet detector gave an absorption maximum of
phosphorus molybdoheteropoly yellow in methyl propionate as shown in Fig. 2.39.
Fig. 2.40 shows good agreement in calibration curves obtained for orthophosphate in
distilled water and in wastewater. Fig. 2.41 shows a typical chromatogram obtained by
this technique.
High performance liquid chromatography has also been used to [237] to determine
orthophosphate, diphosphate and triphosphate.
Speciation and quantitative analysis of orthophosphate, diphosphate and triphosphate
are performed by using high performance liquid chromatography with inductively
coupled argon plasma emission spectrometric detection. High performance liquid
chromatography is used to separate mixtures of phosphates on an anion exchange column
using tartrate magnesium buffer. The inductively coupled plasma is used as a selective
detector by observing P(II) emissions at 214.9nm. The detection limit is 0.5, 1 and 3µg
respectively for ortho-, di- and triphosphate respectively.
Phosphorus was monitored at 214.9nm (second order). The analog signal was taken out
through the profile mode of a computer program. In order to filter noise, a 50KΩ resistor
and 20µF condenser were installed before the recording giving an approximate time
constant of 1s.
Among the eluants examined, oxalate plus magnesium gave the best resolution, tartrate
plus magnesium gave the second best but formate