Chemistry Reference
In-Depth Information
Between 5×10
−5
and 1×10
−2
M nitrate can be determined by this procedure.
Kretzschmar and Kretzschmar [479] have reported an enzymic-photometric method for
the determination of nitrate in non saline waters.
Other techniques for determining nitrate include paper chromatography of diazo dyes
to reduce interference by metals [480], stopped flow analysis [481], direct injection
enthalpimetry [482] and a nitrogen-15 isotopic tracking method [483].
2.63
Nitrite
Analysis of nitrite ion is important due to its role in environmental processes and its
toxicity and suspected carcinogenicity in humans, as
Table 2.37
Effect of diverse species on determination of 0.1mg L
−
1
of nitrite (100ml of
solution extraction method)
Tolerance
limit (ppm)
Species
800
SO
4
2−
, NO
3
, PO
4
3
, HCO
4
, SiO
3
2
150
Mg
2+
, Ca
2+
, Sr
2−
, Ba
2+
, Zr
4+
, Co
2+
, Zn
2+
, Cd
2+
, Hg
2+
, Pb
2+
100
Li
+
, Be
2+
, Cr
3+
, Mo(VI),W(VI), Ni
2+
, Sb
3
−
, Bi
3−
, Se(IV),Te(IV), F, Br
50
Fe
3+
40
I
−+
, aniline, HCHO, phenol
10
SO
3
2−
, SO
2
2
Cu
2−
Source: Reproduced with permission from Elsevier Science [488]
well as its normal function in humans. Measurement of nitrite ion has recently been
examined as a surrogate for in vivo nitric oxide production [484-486]. Sensitive and
selective methods are needed to measure nitrite ion at low levels in the complex matrices
found in water, foods and biological fluids. The wide variety of analytical techniques has
been reviewed recently [487].
2.63.1
Spectrophotometric methods
2.63.1.1
Diazotisation spectrophotometric methods
Spectrophotometric methods for determining nitrite are generally based on conversion of
nitrite to nitrous acid then diazotisation of an aromatic amine by the nitrous acid,
followed by coupling of the diazotised product with an amine or phenol to produce a dye
which is evaluated spectrophotometrically. Numerous diazotisation-coupling reagent
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