Preconcentration techniques - Determination of Anions in Natural and Treated Waters - page 750

Molybdenum blue solvent extraction procedures have also been applied to polluted
waters [69].
Other molybdenum blue solvent extraction-preconcentration proced-ures include the
use of isoamyl alcohol with a pulse polarographic finish [70] and methyl isobutyl ketone
with an inductively coupled plasma atomic emission finish [71,72].
Inductively coupled plasma procedures have the advantage of being applicable to
estuarine as well as river waters. Many of the earlier atomic

Table 15.2 Effect of other ions on phosphorus results (sample, 100ml; DIBK, 5ml; P,
10µg)

Other ion Amount

added

Recovery
(%)

Other ion Amount

added

Recovery
(%)

None - 100 Fe(III) 1mg 101

Cl −

As(V) 0µg 100 2g 101

I -

50µg 102 10mg 102

100µg 105

Br −

10mg 99

As(III) 1mg 104

NO 2 -

10mg 91

104 a

Si 10mg 102 10mg

S 2 O 3 2-

Ge 10mg 101 1g 103

a 20mg of sulphamic acid added
Source: Reproduced with permission from Elsevier Science [71]

absorption procedures had the disadvantage that arsenic, silicon and germanium cause
positive errors because these elements also form reduced heteropoly acids.
Muyazaki et al. [71,72] overcame this problem by determining phosphorus at the P(I)
214.91nm line as the Mo(II) 213.61nm line interferes with the P(I) 213.62nm line.
To achieve the µg L −1 sensitivity they required they incorporated a 100-fold
preconcentration stage into the method. This involved adding molybdate-vanadate
reagent to 500ml water sample, reducing with aconitic acid and extracting to reduced
molybdoantimonyphosphoric acid complex with 5ml diisobutyl ketone.
The effects of other ions are summarised in Table 15.2. No interference from silicon
and germanium (which cause positive errors in the spectrophotometric method) was
observed even at 1000-fold excesses. Arsenic(V) was permissible up to 10 times the
weight of phosphorus. Above this amount, a slight upward background shift was
observed which caused a positive error exceeding 5%.
However, non saline water containing arsenic(V) in amounts more than 10 times that
of phosphorus is rare. Most of the other anions did not show any interference and that of
nitrite was decreased by addition of sulphamic acid. There was no interference from
peroxodisulphate indicating that pretreatment with peroxodisulphate as used for the deter-
mination of total phosphorus in water is also applicable to this method.