United States
Environmental Protection
Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-88/032 Sept. 1988
&EPA Project Summary
An Improved Analytical
Technique for the
Determination of Gas and
Aqueous Phase Hydrogen
Peroxide—Instrument Manual
Purnendu K. Dasgupta
This document describes the con-
struction and operation of an automated
instrument package designed to
measure gaseous and aqueous phase
hydrogen peroxide. The chemical deter-
mination relies on the peroxidase-
medlated conversion of p-hydroxypheny-
lacetic acid to 6,6'-dihydroxy-3,3'-
biphenyldiacetfc acid by H202 and
subsequent base-induced ionization of
all carboxyllc and phenolic protons to
form a fluorescent product. Organic
hydroperoxides (hereafter referred to as
organic peroxides) react in a similar
fashion. The discrimination of H2O2 from
organic peroxides is attained by treating
the sample with granular MnO2 for a
controlled period of time. Such treatment
results in quantitative decomposition of
H2O2 while organic peroxides are virtually
unaffected. The H2O2 concentrations can
thus be computed from the difference
between the value for total peroxides
(untreated sample) and the value for
organic peroxides only (MnO2-treated
sample). Gaseous peroxides are collected
by means of a diffusion scrubber which
is a filament-filled porous membrane tube
suspended concentrically within a polyte-
trafluoroethylene jacket tube. Air is
sampled through the jacket tube so that
it flows around the membrane tube.
Water is pumped through the membrane
tube as the scrubber liquid and collects
peroxides in the sample gas by diffusion
to and through the membrane. The
collected peroxide in the scrubber liquid
is measured by the same liquid phase
chemistry as described above by contin-
uous addition of reagents to the scrubber
effluent. The instrument also contains a
porous membrane-based calibration
source for gaseous H2O2 which relies on
Henry's law. Two inert 3-way solenoid
values provide the diffusion scrubber with
a choice of sample, zero gas or calibrant
in an automated programmable fashion.
The typical detection limit for aqueous
phase H2O2 is 5 nM or 0.17 yug/L (sample
volume 17 /uL). The detection limit for gas
phase H2O2 is 3 x 10 11 v/v (sampling
rate 2 L/min) with a lag time of 1 min
and a 10-99% rise time of 0.8 min.
This Project Summary was developed
by EPA's Atmospheric Sciences Research
Laboratory. Research Triangle Park. NC.
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering at back).
Introduction
Hydrogen peroxide is believed to be a
key oxidant involved in the atmospheric
transformation of gaseous S02 into H2SO4.
Accurate and reliable measurement of
hydrogen peroxide, both in the gas phase
and in precipitation samples, is therefore
important to obtain a complete understan-
ding of the role this apparently ubiquitous
compound plays in the phenomenology of
acid precipitation. There is no commercial
instrumentation available specifically for
this measurement. Although several
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methods of acceptable sensitivity are
available in the literature for the measure-
ment of aqueous hydrogen peroxide,
measurement of gaseous H2O2 is a dif-
ferent problem. Complications are caused
by the requirement of very high sensitivity
(sub parts-per-billion levels must be routine-
ly measured), with a limit of detection
preferably at or below 100 parts per trillion),
presence of organic peroxides in the sam-
ple gas and the formation of hydrogen
peroxide from reactions involving ozone.
For wide applicability, it is desirable to have
a completely automated instrumentation
package with a fabrication cost of approx-
imately under $10,000.
An instrument package that meets the
above criteria has not been developed and
the detailed report provides instructions for
fabrication and operation for such an
instrument.
Procedure
The instrument operates in a differential
manner. Total peroxides and organic perox-
ides in the sample are separately measured
and the difference is taken to be the
measure for hydrogen peroxide. The
organic peroxide signal, by itself, provides
only a lower limit of the organic peroxide
content of the sample; however, the value
obtained for hydrogen peroxide is accurate.
The determination involves reacting
peroxides in the sample with p-hydroxy-
phenylacetic acid in the presence of the en-
zyme catalyst peroxidase at pH 55; the pro-
duct of the reaction 6,6'dihydroxy-3,3-
biphenyldiacetic acid. The reaction stream
passes through a cation exchange mem-
brane tube immersed in concentrated
NH4OH; ammonia permeates inward into
the flow stream and raises the pH to ~ 105.
At this alkaline pH, both the carboxylic and
phenolic protons are ionized and the pro-
duct becomes fluorescent. A cadmium
lamp is used to excite the dimmer at 325
nm and the fluorescence is monitored with
a commercially available flow-through
fluorescence detector with a high-pass
emission filter (50% cutoff wavelength 370
nm).
Hydrogen peroxide and organic perox-
ides are differentiated by measuring the
sample directly (total peroxides) and then
by pretreating the sample through a small
packed bed reactor containing granular
MnO2 which catalytically destroys H2O2
(organic peroxides).
The liquid phase differential analyzer
operates as a flow injection analyzer. A
4-channel peristaltic pump is used for liquid
pumping. Two 6-port electromechanically
actuated rotary valves are used for sample
injection and pretreatment with MnO2. A
microprocessor controlled timer governs
the status of the valves; a sample program
is provided for automated measurement of
total peroxide and organic peroxides by two
successive injections. A sample volume of
17 pL is used with total liquid flow rates
under 100 /iL/min and reagent consump-
tion is thus minimized. The instrument is
capable of 24 injections (12 H2O2 deter-
minations) per hour.
The gas phase differential analyzer
utilizes the same analytical system as the
liquid phase analyzer—a porous mem-
brane based diffusion scrubber provides an
interface for transferring hydrogen perox-
ide to the aqueous phase with reproduci-
ble efficiency. The gas phase analyzer can
be readily transformed to the aqueous
phase analyzer by substituting an injection
valve for the diffusion scrubber.
The diffusion scrubber consists of a
nylon monofilament filled microporous (0.02
/im pores, 40% surface porosity)
polypropylene hollow fiber (400 nm i.d., 450
n9m o.d.) concentrically placed within a
PTFE jacket tube. Tee ports are built into
the jacket tube such that an air sample can
be made to flow around the membrane
tube while water is pumped through the
membrane tube in a countercurrent
fashion. Peroxides in the sample gas are
collected with reproducible efficiency by the
scrubber liquid. Parameters that govern the
exact collection efficiency include mem-
brane length, gas sampling rate, jacket tube
i.d. and diffusion coefficient of the individual
peroxide. Peroxides in the scrubber effluent
liquid is measured by the fluorometric
method described above. Total peroxides
and organic peroxides are measured in-
dividually by allowing the scrubber liquid
to react directly or after passage through
a MnO2 reactor with the fluorescence
derivatization reagent. The gas phase
analyzer contains a porous PTFE mem-
brane based gaseous H2O2 generator that
relies on Henry's law. The output of the
generator is calibrated by bubbler collec-
tion and measurement with the liquid
phase analyzer. Because span drift and
zero drift become the factors which
ultimately control the accuracy and reliabili-
ty of data obtained with any instrument
operated near the limits of its performance,
the gas phase analyzer utilizes alternate
sample/zero sequences (typ. 2 min/4 min)
interspersed periodically with calibrant/zero
sequences. This sequence is automated
with the aid of two PFA-Teflon 3-way
solenoid valves, controlled by a micropro-
cessor driven timer. The valves allow the
passage of ambient sample, zero or cali-
brant gas into the diffusion scrubber.
Results
The detection limit for the aqueous phase
analyzer is 0.17 ^g/L H2O2. The detection
limit for H2O2(g) in the gas phase analyzer
is 3 x 10~11 v/v with a 2 min sample (2L/min
sampling rate). The response time is
reasonably rapid: lag time is 1 min and
10-90% rise time is 0.8 min.
Conclusions
The analyzer developed is a relatively in-
expensive package adaptable for the
measurement of both aqueous and
gaseous phase H2O2. The instrument is
highly sensitive and can be operated in an
automated self-calibrating manner.
Laboratory studies and limited field inter-
comparisons do not show any problems
unique to this instrument. There are no ac-
cepted reference methods for the measure-
ment of trace levels of H2O2 at this time;
thus, it is not possible to completely validate
the results of ambient air sampling.
The Project Report contains fabrication
details, a list of all components, and a list
of vendors. All calibration, reagent purifica-
tion and preparation and maintenance pro-
cedures are discussed. The manual is in-
tended to enable a prospective user to
build, operate, maintain, and troubleshoot
the instrument described in this summary.
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P. K. Dasgupta is with Texas Tech University, Lubbock, TX 79409-1061.
Robert R. Arnts is the EPA Project Officer (see below}.
The complete report, entitled "An Improved Analytical Technique for the
Determination of Gas and Aqueous Phase Hydrogen Peroxide—Instrument
Manual," (Order No. PB 88-239 O25/AS; Cost: $12.95. subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA/600/S3-88/032
0000329 PS
U S EHVIR PROTECTIOI* ftSEKCY
CHICAGO
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