Anions in seawater - Determination of Anions in Natural and Treated Waters - page 400

sample.
Flynn and Meehan [175] have described a solvent extraction phosphomolybdate
method using iso amyl alcohol for monitoring the concentration of 32 P in sea and coastal
waters near nuclear generating stations.
Fujiwara et al. [176] have proposed a method for the colorimetric determination of
traces of phosphorus with molybdenum blue, making use of the laser-induced thermal
lensing effect. The procedure is described, and the results obtained on samples of sea
water and lake water are presented.
In this method an Ar + laser pumped rhodamine 101 laser was used as the heat and
probe source. The signal from a silicon photocell with a 1mm 2 photosensitive surface,
which was used as a laser radiation detector, was processed with an inexpensive personal
computer. The detection limit is 5pg of P mL −1 which is determined mainly due to the
deviation in the colour development with the molybdenum blue method.
Yoshimura et al. [177] carried out microdeterminations of phosphate by gel-phase
colorimetry with molybdenum blue. In this method phosphate reacted with molybdate in
acidic conditions to produce 12-molybdophos-phate. The blue species of
molybdophosphate were reduced by ascorbic acid in the presence of antimonyl ions and
adsorbed on Sephadex G-25 gel beads. Attenuation at 836 and 416nm (adsorption
maximum and minimum wavelengths) was measured and the difference used to
determine trace levels of phosphate. The effects of nitrate, sulphate, silicic acid, arsenate,
aluminium, titanium, iron, manganese, copper and humic acid on the determination were
examined.
Eberlein and Kattner [178] have described an automated method for the determination
of orthophosphate and total dissolved phosphorus in the marine environment. Separate
aliquots of filtered seawater samples were used for the determination of orthophosphate
and total dissolved phosphorus in the concentration range 0.01-5µg L −1 phosphorus. The
digestion mixture for total dissolved phosphorus consisted of sodium hydroxide (1.5g),
potassium peroxidisulphate (5g) and boric acid (3g) dissolved in doubly distilled water
(100ml). Seawater samples (50ml) were mixed with the digestion reagent, heated under
pressure at 115-120°C for 2h, cooled and stored before determination in the autoanalyser
system. For total phosphorus, extra ascorbic acid was added to the aerosol water of the
autoanalyser manifold before the reagents of the molybdenum blue reaction were added.
For the measurement of orthophosphate, a phosphate working reagent composed of
sulphuric acid, ammonium molybdate, ascorbic acid and antimony potassium tartrate
solution was prepared. Up to 30 samples per h could be analysed.
The application of this technique is discussed under multianion analysis in section
3.32.1.
3.24.2 Reverse flow injection analysis
This technique differs from flow injection analysis in the sense that whereas in the latter
technique the sample plug is injected into a flowing stream of reagent, in the former
technique plugs of reagent are injected into a continuous stream of the sample. Under
these conditions the amount of sample in the zone of the reagent will increase as the
dispersion increases. The sample will become well mixed with the reagent as its