Anions in wastewaters - Determination of Anions in Natural and Treated Waters - page 561

13.2.2.1.

8.17.6 High performance liquid chromatography
The methods developed by Sakurai et al. [89] and Morgan and Danielson [90] are also
applicable to the determination of respectively, phosphates in waste waters and in sewage
effluents.

8.17.7 Sample preservation
Rossin and Lester [91] evaluated some of the methods available for the preservation of
condensed phosphates in samples of domestic waste waters, ie the prevention of the
hydrolysis of condensed phosphate to orthophosphate. They showed that mercuric
chloride at 40mg L −1 at normal pH is the most effective preservative examined for
samples stored at 20°C for 6 days (Table 8.21). Samples should be filtered as soon as
possible after they have been taken. Mercuric chloride at high pH was not a satisfactory
preservative. Addition of sodium hydroxide to raise the pH increases phosphatase activity
but lowers the rate of spontaneous hydrolysis and, on balance, is not a satisfactory
treatment. Formaldehyde at elevated pH was less efficient than mercuric chloride at
normal pH.
The samples treated with mercuric chloride at normal pH presented the smallest
difference from the mean with a range between −0.07 and +0.06. When formaldehyde
was used at high pH, the range was between −0.16 and 0.00. The samples containing
mercuric chloride at pH 10 showed a range between −0.15 and +0.21. A variation
between −0.21 and +0.35 was found when pH was increased in the filtered samples. The
use of formaldehyde at normal pH resulted in a variation between −0.25 and +0.34.

8.18 Phosphite

8.18.1 X-ray fluorescence spectroscopy
Taira et al. [92] reported an X-ray fluorescence spectrometric determination of phosphite
(HPO 3 2− ) in electrodeless plating process wastewater in which the phosphite was
precipitated with iron(III), followed by collection on a

Table 8.21 Concentration of orthophosphate in settled sewage samples, filtered and
unfiltered, with different preservatives, analysed at different times

Orthophosphate as P mg L −1 after storage

Sample

0 1 day 3 days 6 days Mean

Settled unfiltered 5.26 5.96 6.33 6.33 -

Sewage filtered 4.28 4.20 4.48 4.74 -