Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 264

2.75.9 Enzymic methods
Enzymic methods have been developed for the determination of phosphates in non saline
waters. Stevens [645] gives details of an automated enzymatic method for determination
of orthophosphate. Results of analysis of water samples by this method and by the
soluble reactive phosphorus method indicated that a form of phosphorus was present
which was determined as soluble reactive phosphorus but not as enzymatic
orthophosphate; the presence of an hydrous ferric oxide-orthophosphate complex is
postulated.
Steinberg et al. [646] described an automated enzymic method for phosphate based on
the property of orthophosphate of inhibiting the hydrolysis of certain fluorogenic
substrates by means of the alkaline phosphatase of Esch. coli . A particular substrate is 4-
methylumbelliferyl phosphate which has a maximal excitation frequency of 360nm.
Results obtained are compared with values given by the molybdenum blue method,
which point to discrepancies in the latter. A detection limit of 0.1µg L −1 phosphate
phosphorus is reported.
Chrost et al. [647] described a method for determining enzymically hydrolysable
phosphate based on determination of inorganic phosphate released after the hydrolysis of
organophosphoric esters by free, dissolved phosphohydrolases (mainly phosphatase)
produced by biota. The method gave higher values in hypereutrophic waters than the
molybdenum blue procedures and similar values for less eutrophic waters. The method
was recommended for eutrophic waters where the orthophosphate concentration
exceeded 25µg L −1 phosphorus.
2.75.10 Ion chromatography
Various workers have applied this technique to the determination of phosphate in non
saline waters [648-650].
The application of this technique is discussed under multianion analysis in sections
12.2.1, 12.2.4, 12.2.5 and 12.2.6.
2.75.11 High performance liquid chromatography
Sakurai et al. [651] have described a high performance liquid chromatographic procedure
for the determination of down to 0.5mg L −1 phosphate in waste water and river waters.
The method is based on the solvent extraction of molybdoheteropoly yellow with methyl
propionate. 0000