Chemistry Reference
In-Depth Information
Table 2.12
Major environmental factors affecting the hydrolytic degradation of
condensed phosphates
Factor
Approximate effect on rate
10
5
-10
6
faster from freezing to boiling
Temperature
10
3
-10
4
slower from strong acid to base
pH
As much as 10
5
-10
6
faster
Enzymes
As much as 10
4
-10
5
faster
Colloidal gels
Complexing cations
Very many-fold faster in most cases
Concentration
Roughly proportional
Ionic environment in the solution
Several-fold change
Source: Own files
Tripolyphosphoric acid is represented as H
5
P
3
O
10
(3H
3
PO
4
-2H
2
O). The three forms of
tripolyphosphate are:
H
3
P
3
O
10
2−
, H
2
P
3
O
10
3−
and HP
3
O
10
4−
A number of factors affect the rate at which condensed and organic phosphates undergo
hydrolytic degradation in aqueous solution. The major environmental factors in
decreasing order of effectiveness are listed in Table 2.12. Consideration of Table 2.12
indicates that pH is one of the factors which exerts a considerable influence on the rate of
hydrolysis.
In domestic waste waters, all these factors may influence the hydrolysis of condensed
phosphate to orthophosphate. Thus if the sample is not analysed immediately, changes in
the concentrations of condensed and orthophosphates will occur. If the forms of
phosphate are to be determined rather than total phosphate, hydrolysis must be prevented.
2.22.1
High performance liquid chromatography
High performance liquid chromatography has also been used [237] to determine
orthophosphate, pyrophosphate and tripolyphosphate.
Speciation and quantitative analysis of orthophosphate, pyrophosphate and
tripolyphosphate 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 ICP 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-, pyro- and tripolyphosphate respectively.
In this procedure a Waters Associates liquid chromatograph was connected to anion
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