Environmental Engineering Reference
In-Depth Information
Table 8.5 Spectrometric (colorimetric) methods for the analysis of pollutants in water
EPA
Pollutant
Method description
method
Ammonia
Alkaline Hg(II) iodide reacts with ammonia, producing
350.2
colloidal orange-brown NH 2 Hg 2 I 3 , which absorbs light
at l 400 and 500 nm
Arsenic
Reaction of arsine, AsH 3 , with silver diethylthiocarbamate
206.4
in pyridine, forming a red complex (l ¼ 535 nm)
Boron
Reaction with curcumin, forming red rosocyanine
212.3
(l ¼ 540 nm)
Cl liberates thiocyante (SCN ) from mercuric thiocyanate.
Chloride
325.1-2
The SCN forms highly colored ferric thiocyanate
(l ¼ 480 nm)
Chromium
Reacts with 1,5-diphenylcarbohydrazide to form a purple
7196
color complex (l ¼ 540 nm)
Cyanide
Formation of a blue dye from reaction of cyanogen
335.2
chloride, CNCl, with pyridine-pyrazolone reagent
(l ¼ 620 nm)
Fluoride
Decolorization of a zirconium-dye colloidal precipitate
340.1
(l ¼ 570 nm) by formation of colorless zirconium
fluoride and free dye
NO 3 is reduced to NO 2 , which is diazotized with
Nitrate
353.1
and nitrite
sulfanilamide and coupled with N -(1-naphthyl)-
ethylenediamine dihydrochloride to produce a highly
colored azo dye ( l ¼ 540 nm)
Phenol
Reaction with 4-aminoantipyrine (pH 10) in the presence
420.1
of K 3 Fe(CN) 6 forming an antipyrine dye that is extracted
into pyridine (l ¼ 460 nm)
Phosphate
Reaction with molybdate ion to form a phosphomolybdate
365.1-3
that is selectively reduced to intensely colored
molybdenum blue (l ¼ 690 nm)
Silica
Formation of molybdosilicic acid with molybdate followed
370.1
by reaction to a heteropoly blue (l ¼ 650 or 815 nm).
Sulfide
Sulfide reacts with dimethyl-p -penylenediamine in the
376.2
presence of ferric chloride to produce methylene blue
( l ¼ 625 nm)
Surfactants
Reaction with methylene blue to form blue salt (l ¼ 652 nm)
425.1
Digestion in sulfuric acid to NH 4 followed by treatment
Total Kjeldahl
351.1
nitrogen
with alkaline phenol and sodium hypochlorite to form
blue indophenol (l ¼ 630 nm)
Ozone (O 3 ) : Potassium iodide (KI) is used to scrub O 3 from air. The
resulting I 2 can be measured by a spectrometric method.
2KI þO 3 þH 2 O ! 2 KOHþO 2 þ I 2
ð8
:
11Þ
I 2 þ starch ! blue
=
purple complex
ð8
:
12Þ
 
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