Chemistry Reference
In-Depth Information
2.75.4
Atomic absorption spectrometry
Phosphate (and arsenate and arsenite) have been determined in non saline waters by a
technique based on flotation spectrometry and extraction-indirect atomic absorption
spectrometry using malachite green as an ion-pairing reagent [641].
2.75.5
Polarography
Hight
et al.
[642] give details of a procedure for the determination of phosphate in
aqueous samples by differential pulse polarography, based on determination of
molybdenum in 2-phosphomolybdic acid. Phosphate is first converted to the
phosphomolybdate complex which is then extracted into iso-butyl acetate. High
sensitivity is achieved by measuring the polarographic wave due to the catalytic reduction
of perchlorate or nitrate in the presence of molybdenum(VI). The method is suitable for
samples as small as 3.5ml which contain as little as 9µg L
−1
of phosphorus. The average
relative deviation is 3.0% at the 0.045mg L
−1
phosphorus level and 1.6% at the 1-2mg
L
−1
level.
Iso-butyl acetate is then removed by evaporation and the residue dissolved in dilute
sodium hydroxide, followed by acidification with perchloric acid. Phosphate is then
determined indirectly by measurement of the catalytic current of perchlorate or nitrate in
association with molybdenum(VI).
2.75.6
Anodic scanning voltammetry
Matsunaga
et al.
[643] have discussed the differential pulse anodic voltammetry of
phosphates.
2.75.7
Column coupling isotachophoresis
This technique offers very similar advantages to ion chromatography in the determination
of anions in water, namely multiple ion analysis, little or no sample pretreatment, speed,
sensitivity and automation. Very similar advantages are offered by capillary
isotachophoresis. Zelinski
et al.
[325] applied the technique to the determination of 0.02-
0.1mg L
−1
quantities of phosphate, chloride, fluoride, nitrate, nitrite and sulphate in river
waters.
The application of this technique is also discussed under multianion analysis in section
14.6.1.1.
2.75.8
X-ray fluorescence spectroscopy
Yamamoto [644] precipitated trace amounts of phosphate in river water by adding
ammonium molybdate and 8-quinolinol to form (C
9
H
7
ON)
3
.H
7
[P(Mo
2
-O
7
)
6
].2H
2
O. The
precipitate was collected on a membrane filter and the phosphorus was determined by X-
ray fluorescence spectrometry. The calibration curve was linear over the range of 0.3-
10µg of phosphate. Iron(III) (<0.15mg) and lead (<0.3mg) did not interfere.
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