Chemistry Reference
In-Depth Information
Ion
HCO
3
-
6mg
Al
3+
3mg
Fe
3+
, Co
2+
, Ni
2+
, Cu
2+
, Zn
2+
, Ca
2+
, K
+
, NO
3
-
1mg
Mg
2+
, Na
+
, NH
4
+
0.5mg
Si(IV)
15µg
ClO
4
−
5µg
W(VI)
4µg
As(V)
2µg
V(V)
1µg
a
The tolerance limit is defined as the concentration level at which the interference causes an error
of not more than ±2%
Source: Reproduced with permission from the Royal Society of Chemistry [622]
Matsubara
et al.
[623] have described a rapid method for the determination of trace
amounts of phosphate (and arsenate) in water by spectrophotometric detection of their
heteropoly acid-malachite green aggregates following preconcentration by membrane
filtration.
The application of this technique is also discussed under multianion analysis in
sections 14.2.1.1 and 14.2.2.1.
2.75.2
Spectrofluorometric methods
Several types of method for the determination of orthophosphate exploit the high
sensitivity of fluorometric techniques. The ability of phosphate to inhibit the fluorescence
of chelates led to the investigation of various metal-chelate systems for maximum
sensitivity in the detection of trace amounts of phosphate. Several metal chelates of
aluminium, gallium and zirconium with morin, 3-hydroxyflavone and quercetin have
been examined but none proved as satisfactory as aluminium-morin for the determination
of phosphate. Strongly complexing, coloured and metallic ions have a detrimental effect
on this method. For the technique to be specific, phosphate must be separated from a
number of cations and anions that interfere in the fluorometric analysis.
The enzymatic method proposed by Shulz
et al.
[624] with glycogen is specific but the
treatment is too slow. This selective method for determining inorganic phosphate is based
on a series of three enzymic reactions at neutral pH. Glycogen phosphorylase is used to
catalyse the reaction between inorganic phosphorus (P
1
) and glycogen, forming glucose-
1-phosphate, which with phosphoglucomutase is converted into glucose-6-phosphate.
Finally, with glucose-6-phosphate dehydrogenase and the addition of NADP, 6-P-
gluconolactone and NADPH
2
are formed in proportion to the inorganic phosphate
present:
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