Environmental Engineering Reference
In-Depth Information
8.2.2 UV-VIS as a Workhorse in Environmental Analysis
The U.S. EPA has adopted a number of spectrophotometric methods for the
determination of pollutants in both air and water (Manahan, 2005). In the following
discussions, we first summarize EPA methods (Tables 8.4 and 8.5), then briefly
introduce the chemical principles (with an emphasis on visible colorimetric
methods). We will focus on the chemical principles since operation details can
always be found in cookbooks of these standard methods.
Table 8.4 Spectrometric (colorimetric) methods for the analysis of pollutants in air
Pollutant
Method
EPA method no.
SO
2
Pararosaniline (colorimetric)
40 CFR 50 Appendix A
O
3
Potassium iodide reaction (colorimetric)
40 CFR 50 Appendix E
NO
2
Azo dye reaction (colorimetric)
40 CFR 50 Appendix F
UV-VIS Methods for Atmospheric Pollutants
The spectrometric methods in Table 8.4 specify reference analytical methods by the
U.S. EPA. These methods are published in CFR. Although they are not necessarily
technically advanced, for regulatory and legal purposes,
they provide reliable
measurement proven to be valid.
Sulfur dioxide (SO
2
)
: This cumbersome EPA reference method uses an
impinger (Fig. 4.9c) to scrub air samples through a collection solution
containing tetrachloromercurate or formaldehyde. The reaction with SO
2
results in the oxidation of sulfite to bisulfite:
2
2
þ4Cl
þ4H
þ
½HgCl
4
þ2SO
2
þ2H
2
O !½HgðSO
3
Þ
2
ð8
:
8Þ
SO
2
þCH
2
OþH
2
O ! HOCH
2
SO
3
H
ð8
:
9Þ
The red-purple pararosaniline methylsulfonic acid is formed when acid-bleached
pararosaniline and formaldehyde scrubbed the solution containing a stable,
nonvolatile dichlorosulfitomercurate (West and Gaeke, 1956).
NH
2
NHCH
2
SO
3
H
+ 3HOCH
2
SO
3
H
OH
HN
NHCH
2
SO
3
H
H
2
N
NH
2
CH
2
SO
3
H
p
-Rosaniline
ð8
:
10Þ
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