Environmental Engineering Reference
In-Depth Information
H
2
O
2
standard solution
: A 1
×
10
−
2
M H
2
O
2
standard stock solution is
prepared by diluting 1.0 mL of 30 % H
2
O
2
to 100 mL with ultrapure water. The
concentration of H
2
O
2
is determined based on the molar extinction coefficient at
240 nm (
ε
=
38.1 L mol
−
1
cm
−
1
) (Miller and Kester
1988
).
HPLC system
: An HPLC-fluorescence system is adopted. The separa-
tion is carried out on a RP-C18 column with acetonitrile-water mixture as elu-
ent. Tentative elution conditions are (CH
3
CN/H
2
O 40/60 v/v) at a flow rate of
1 mL min
−
1
(note: optimal conditions may vary depending on the actual system
adopted). For the detection of phenol, the fluorescence detector is operated at 270
and 298 nm for excitation and emission, respectively.
Analytical procedure
: 3.0 mL of water sample (natural water or standard
H
2
O
2
) is first treated with 200
μ
L of 2
×
10
−
2
M benzene in a 5 mL amber vial
and then mixed by gently shaking. It is then added 50
μ
L of 0.1 M Fe
2
+
in 0.07 M
H
2
SO
4
solution, waiting 5 min at room temperature for completion of the Fenton
reaction. The final pH of the solution should be adjusted to ca. 4 with addition of
sulphuric acid solution. It can be noted that the rate constant of the Fenton reac-
tion is much higher at pH 4 to 5 than at pH 3, thus the reaction can be conducted
in these pH ranges. An aliquot of the solution (e.g. 150
μ
L) is then injected into
the HPLC system for analysis. Phenol and benzene are separated by reverse-phase
chromatography. The standard phenol and H
2
O
2
concentrations might be 0, 100,
200, 300, 500 and 1000 nM, and can be prepared freshly by diluting their stock
solutions. The H
2
O
2
concentration is determined by calibration of the peak areas
of phenol produced in each standard solution against the H
2
O
2
concentration of
the sample. It can be noted that the addition of 10
μ
M NO
2
−
to the water samples
shows no significant interference on the fluorescence intensity of phenol. In con-
trast, addition of 50
μ
M NO
2
−
to the samples decreases the fluorescence intensity
signal of phenol by almost 40 %.
3 Mechanism of Production of H
2
O
2
and ROOH
in Natural Waters
3.1 Photoinduced Formation of H
2
O
2
and ROOH
H
2
O
2
and ROOH are photolytically produced by several pathways in the aquatic
environments. First, H
2
O
2
and ROOH are photogenerated by chromophoric or flu-
orescent dissolved organic matter (CDOM or FDOM) in aqueous media (Cooper
and Zika
1983
; Mostofa and Sakugawa
2009
; Moore et al.
1993
; Richard et al.
2007
; Baxter and Carey
1983
; Clark et al.
2009
; Cooper et al.
1989a
,
b
; Dalrymple
et al.
2010
). A second pathway is linked with the redox cycling of transition metal
ions in aqueous media (Moffett and Zika
1983
; Moffett and Zika
1987a
,
b
). An
additional process is the intracellular H
2
O
2
formation in chloropigments in aquatic
organisms (Lobanov et al.
2008
; Hong et al.
1987
; Bazanov et al.
1999
). Finally,
