Tennessee
Valley
Authority
United States
Environmental Protection
Agency
Division of Environmental
Planning
Chattanooga, Tennessee 37401
Office of
Research and Development
Washington, D.C. 20460
E-LB-76-1
EPA-600/7-76-005
JULY 1976
VOLTAM METRIC
DETERMINATION
OFACROLEIN
Interagency
Energy-Environment
Research and Development
Program Report
/
7_
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S.
Environmental Protection Agency, have been grouped into seven series.
These seven broad categories were established to facilitate further
development and application of environmental technology. Elimination
of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The seven series
are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from
the effort funded under the 17-agency Federal Energy/Environment
Research and Development Program. These studies relate to EPA's
mission to protect the public health and welfare from adverse effects
of pollutants associated with energy systems. The goal of the Program
is to assure the rapid development of domestic energy supplies in an
environmentally—compatible manner by providing the necessary
environmental data and control technology. Investigations include
analyses of the transport of energy-related pollutants and their health
and ecological effects; assessments of, and development of, control
technologies for energy systems; and integrated assessments of a wide
range of energy-related environmental issues.
This document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161.
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E-EP-76-01
EPA-600/7-76.005
July 1976
yOLTAMMETRIC DETERMINATION
OF ACROLEIN
by
Lyman H. Howe
Division of Environmental Planning
Tennessee Valley Authority
Chattanooga, Tennessee 37401
Interagency Agreement No. D6-E721
Project No. E-AP 78BDH
Program Element No. EHE 625C
Project Officer
Gregory D'Alessio
Office of Energy, Minerals, and Industry
U.S. Environmental Protection Agency
Washington, D.C. 20460
This study was conducted
as part of the Federal
Interagency Energy/Environment
Research and Development Program.
Prepared for
OFFICE OF ENERGY, MINERALS, AND INDUSTRY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
-------
DISCLAIMER
This report has been reviewed by the Office of Energy,
Minerals, and Industry, U.S. Environmental Protection
Agency, and approved for publication. Mention of trade
names or commercial products does not constitute endorsement
or recommendation for use.
11
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ABSTRACT
A differential pulse polarographic method was developed for
determining concentrations of acrolein in natural waters and
in condenser cooling water. Acrolein is electrochemically
reduced at negative potentials at the dropping mercury
electrode. The height of the polarographic peak versus the
saturated calomel electrode (SCE) is measured and referred
to a standard curve. The range of this method is from 0.05
to 0.5 milligrams per liter (mg/1) of acrolein.
Acrolein concentrations can also be determined by
differential pulse voltammetry at the glassy carbon
electrode. Acrolein is measured indirectly by forming the
acrolein-sulfite complex; unreacted sulfite is determined by
measuring the oxidizing current at positive potentials in a
buffer solution. This procedure does not require lengthy
deaeration to remove oxygen, but its poor sensitivity
(10 mg/1) makes it less attractive than the polarographic
method.
Acrolein formed a complex with sulfite and could not be
recovered at 0.5 mg/1 from samples preserved with excess
sulfite.
This report was submitted by the Tennessee Valley Authority,
Division of Environmental Planning, in partial fulfillment
of Energy Accomplishment Plan 78BDH under terms of
Interagency Energy Agreement D6-E721 with the Environmental
Protection Agency. Work was completed as of July 1975.
111
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CONTENTS
Paqe
Abstract ii
List of Figures iv
List of Tables iv
Sections
I Conclusions 1
II Recommendations 2
III Introduction 3
IV Experimental 6
Apparatus 6
Reagents 7
Procedure 11
V Results and Discussion 13
Voltammetry at Negative Potentials with the
Dropping Mercury Electrode (Polarography) 13
Voltaminetry at Positive Potentials with
the Glassy Carbon Electrode 20
Preservation with Sulfite , 28
References 33
List of Publications 37
Glossary 38
Appendix 40
v
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FIGURES
No. Page
1 Calibration Curve for Acrolein 14
2 Polarograms for Acrolein with Dropping
Mercury Electrode 15
3 Vcltammogram of Sulfite at pH 7 with
Glassy Carbon Electrode 22
4 Voltammogram of Sulfite at pH 13
with Glassy Carbon Electrode 24
5 Voltanunogram of Sulfite at pH 4
with Glassy Carbon Electrode 26
6 Vcltammogram of Sulfite at pH 1
with Glassy Carbon Electrode 27
7 Polarogram for Acrolein in Excess Sulfite
at pH 1 with Dropping Mercury Electrode .... 29
8 Polarogram for Acrolein at pH 1 with
Dropping Mercury Electrode 31
TABLES
Bisulfite Assay Results
for Acrolein 8
Preparation of Phosphate Euffer
Solutions for Tests of the Effects
of pH on Polarographic Determination
of Acrolein 10
Test Results for Acrolein Demand
after One Hour for Split Samples of
Surface Waters with 0.30 mg/1 Acrolein
Added 17
VI
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SECTION I
CONCLUSIONS
With a method based on electrochemical reduction at the
dropping mercury electrode, acrolein can be determined at
concentrations between 0.05 and 0.5 mg/1 in both natural
waters and in condenser cooling water by differential pulse
polarography (voltammetry at the dropping mercury
electrode). The sample for acrolein analysis is buffered at
pH 7.2 with 0.09 mole per liter (molar, M) phosphate, and
ethylenediaminetetraacetic acid (EDTA) is added in a
concentration of 0.09 percent (%) to prevent interference
from zinc. Tne height of the peak current at about -1.2
volts versus a calomel electrode filled with saturated
sodium chloride [V vs. S.C. E. (NaCl) ] is compared with a
standard curve. The recovery of acrolein is unaffected by
changes in pH between 6.8 and 7.6 or by concentrations of
zinc as high as 2.0 mg/1. Replicate analyses showed that
acrolein could be determined accurately at concentrations of
0.1 and 0.3 mg/1 with standard deviations of 0.008 and 0.013
mg/1, respectively. The recommended method is given in the
appendix.
Differential pulse voltammetry at the glassy carbon
electrode allows the determination of acrolein with a
sensitivity of 10 mg/1. Acrolein is reacted with excess
sulfite, and the unreacted sulfite is determined by
measuring the oxidizing current at +0.6 V vs. S.C.E. (NaCl)
in 0.09 M phosphate at pH 7.2. Although this metnod does
not require extensive deaeration, it is less sensitive than
the recommended method.
Sulfite, which forms a complex with acrolein, was tested as
a preservative for water samples taken for analysis of low
levels of acrolein. However, acrolein could not be
recovered from solutions containing excess sulfite; at most,
only 15ft of the acrolein was recovered. Because attempts to
break the acrolein-sulfite complex were not successful,
sulfite is not recommended for preserving acrolein.
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SECTION II
RECOMMENDATIONS
Differential pulse voltammetry at the dropping mercury
electrode (polarography) is the recommended method for
determining acrolein at concentrations from 0.05 to 0.5 mg/1
in natural or condenser cooling waters. The method is
presented in the appendix. This method was studied for
analysis of water associated with steam-electric generating
stations. It was not within the scope of this project to
test its applicability to other industrial and domestic
waste waters, but it is recommended that this testing be
performed.
Acrolein can also be determined by differential pulse
voltammetry at positive potentials at the glassy carbon
electrode. Acrolein is reacted with excess sulfite, and the
unreacted sulfite is determined by measuring the oxidizing
current. Because of the poor sensitivity (10 mg/1), the
procedure was not evaluated for analyzing natural and
condenser cooling waters. The sensitivity of the technique
might be improved with another electrode (for example, the
graphite electrode impregnated with styrene and irradiated
with cobalt 60). The technique may be applicable to
monitoring sulfur dioxide. The information contained herein
on the reaction of acrolein with sulfite may be valuable in
evaluating, by bioassay, the effect of sulfite in
neutralizing acrolein toxicity.
Sulfite is not recommended as a preservative for acrolein
solutions because acrolein formed a complex with excess
sulfite and could not be recovered by any of the techniques
tested.
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SECTION III
INTRODUCTION
Acrolein is an olefinic aldehyde with the chemical name
propenal. It is registered for use in controlling slime
growths. It also has potential for use as a molluscicide
for controlling Asiatic clams in the heat exchangers and
other service water systems at steam-electric generating
stations; however, it is not now registered for this
application. Acrolein is toxic, but it is rapidly
dissipated in the environment. Knowing the quantity of
acrolein dissipated in the test water (acrolein demand) and
the dilution factor, one can readily calculate residuals in
the environment. Walko1 discussed the advantages that
acrolein has over chlorine for controlling mussels and
Asiatic clams.
Sensitive and rapid analytical methods that are accurate and
precise are needed for monitoring acrolein in the
environment. A number of methods have been devised for
measuring concentrations of acrolein.
Cohen's2 spectrophotometric method, which traps acrolein in
the colorimetric reagent 4-hexylresorcinol, is the standard
for measuring concentrations of acrolein in air, and it is
approved by the Intersociety Committee3 as a tentative
method. At the Eetz Laboratories, this method is used for
determining acrolein in water.* The acrolein is separated
from water by distilling it into the colorimetric reagent;
the sample is then visually compared with standards,
Spectrometric measurement5 can be used instead of visual
comparison.
For acrolein concentrations near 0.3 mg/1, tne dosage that
has been used to control slime growths and that may be
useful for controlling infestations of Asiatic clams,1 the
Betz Laboratories method frequently produced erratic
results. Furthermore, the distillation and color
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development steps were time-consuming. Therefore, TVA
searched the literature for a better method.
Verhaar6 used gas chromatography to determine acrolein
concentrations in the combustion products of propylene.
Smythe7 determined acrolein concentrations in diesel engine
exhausts by means of a gas chromatographic procedure based
on the volatility of the hydrazone derivative of acrolein.
These methods have not been applied to the determination of
acrolein concentrations in water.
One reported colorimetric method8 measures the absorbance of
the hydrazone derivative to determine concentrations of
acrolein in water. This method/ although adequately
sensitive, is very time-consuming.
Moshier9 reported a polarographic method for assaying
acrolein in water with a detection limit of 10 mg/1. Van
Sandt1° improved Moshier's method to achieve a detection
limit of 1 mg/1, but this sensitivity is still not
sufficient for monitoring an acrolein concentration of 0.30
mg/1.
With differential pulse polarography, an extremely sensitive
and economical analytical tool,11 it should be possible to
improve the sensitivity of the Van Sandt method1o to 0.05
mg/1. The theory and practice of differential pulse
polarography are given in the literature. u-i f
One difficulty in the use of low-level polarographic
analysis is the interference of dissolved oxygen.18 Oxygen
must be removed by sparging with nitrogen that has been
scrupulously purified to remove all traces of oxygen.
Lengthy deaeration, however, is unnecessary at potentials
greater than about +0.1 volts versus a calomel electrode
filled with saturated potassium chloride (V vs. S.C.E.). At
positive potentials, the mercury electrode is analytically
worthless,18 but the glassy carbon electrode produces
suitable results.19 Tables of the voltammetric behavior of
organic compounds at solid electrodes2o contain no
information on the direct determination of acrolein by
oxidation at positive potentials. An indirect determination
involving coulometry with bromine is reported,21 but this
method is not specific for acrolein.
These findings suggested an investigation of the voltammetry
of acrolein using the glassy carton electrode. A possible
approach to the electroanalysis of acrolein, not mentioned
-------
in the literature, could be based on the acrolein complex
with sulfite.*f22»23 Either a direct determination of the
complex, should it prove to be electroactive, or an indirect
measurement of unreacted sulfite might be possible.
The electrochemical behavior of sulfite at the glassy carbon
electrode has not been investigated, nor has the behavior of
the acidic forms of sulfite (bisulfite and sulfur dioxide).
Theoretically, sulfite should oxidize readily at the carbon
electrode, because its standard potential in base is +0.69
V vs. S.C.E.21 Sulfur dioxide, the conjugate acid of
sulfite, is electrochemically active at the platinum
membrane electrode.20 The voltammetric determination of
sulfur dioxide by coulometric generation of bromine at
positive potentials is well known,21 and instruments for
monitoring sulfur dioxide in air have been based on that
principle.24/25 Sulfur dioxide has been determined by
differential pulse polarography in nonaqueous solvents.26
Because acrolein readily decomposes, even when preserved
with 0.1 JS weight expressed as a fraction of total volume
(w/v) hydroquinone,22 samples with acrolein must be analyzed
immediately. About one-third of the acrolein at the
1.0-mg/l level in a sealed volumetric flask filled to the
mark is lost within 4 days.1 Jackson27 suggested sulfite at
pH 7 as a potential preservative for low levels of acrolein,
about 0.5 mg/1 and below, and regeneration of the acrolein
for analysis by distillation at pH 1 or 13. Sulfite in a
concentration of 1% (w/v) sodium bisulfite plus
refrigeration at 6 degrees Celsius (°C) is a known method
for preserving high levels of acrolein, about 2 mg/1 and
above, in aqueous solutions impinged from air.2a
Based on the foregoing literature review, the goals of this
research were (1) to develop a method capable of determining
acrolein in concentrations as low as 0.05 mg/1 by
differential pulse voltammetry with the dropping mercury
electrode (pclarographic method) at negative potentials
after removing oxygen; (2) to develop a voltammetric method
for determining acrolein, either directly or indirectly with
sulfite, with the glassy carbon electrode at positive
potentials without removing oxygen; and (3) to test the
effectiveness of sulfite as a preservative for acrolein in
solution at the 0.5-mg/l level.
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SECTION IV
EXPERIMENTAL
APPARATUS
All measurements were made with the Princeton Applied
Research (PAF) Model 174 Polarographic Analyzer with
mechanical drop timer and Houston Omnigraphic X-Y Recorder
Model 2200-3-3. The dropping mercury electrode was a 2- to
5-second capillary from Sargent-Welch Company with Part No.
S-29419. The glassy carbon electrode was obtained from PAR,
as were the carbon counter electrode, the salt bridge with
isolation frit, the saturated calomel electrode, the
outgassing tube, the cell holder, the cell, and other
electrochemical accessories.*9
Nitrogen gas used to deaerate solutions for polarographic
analysis was purged of oxygen. Zero-grade nitrogen gas was
passed through a furnace containing a special catalytic
converter (Model 02-2315 Gas Purifier purchased from
Supelco, Bellefonte, Pennsylvania) and heated to 600°C. The
gaseous effluent from the furnace was successively passed
through a Hydro-Purge unit and a Dow gas purifier, both of
whicn are available from Applied Science Laboratories, State
College, Pennsylvania. The gas was then passed through
sintered glass frits in three scrubbing towers, two
containing 100 milliliters (ml) of 0.1 M chromous chloride
in 2.4 M hydrochloric acid with amalgamated zinc and one
containing 100 ml of reagent water. The amalgamated zinc
was 0.8-3.2 millimeter (mm) pore size for a Jones reductor
(Fisher Scientific Company, Fairlawn, New Jersey). Details
for preparing the chromous chloride scrubbers are given by
Meites.l B
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REAGENTS
All chemicals were reagent grade and, except for acrolein,
were used without further purification. Reagent water was
used throughout this study. It was dispensed from a Super-Q
system manufactured by Millipore Corporation, Bedford,
Massachusetts. The system purifies tap water by filtration,
adsorption on activated carbon, mixed-bed ion exchange, and
final filtration through a 0.8-micrometer (ym) membrane
filter.
Purification and Assay of Acrolein
The acrolein used in this study was distilled, and the
fraction that boiled at 51-53 °C was collected in sufficient
hydroquinone to provide a final concentration of 0.1 fc w/v
hydroquinone.
CAUTION
Acrolein is a powerful lacrimator and ir-
ritates the skin. Handle with gloves in a
ventilated hood. Acrolein also, when hot
and concentrated, may react explosively
with oxidants, bisulfates, or other
chemicals. It is also very flammable.
The acrolein in the clear distillate was assayed with
bisulfite.23 As detailed by Siggia,23 the bisulfite was
generated in a 500-ml glass-stoppered Erlenmeyer flask by
adding, while the contents were being stirred, 50 ml of
standard 1 N sulfuric acid to 250 ml of 1 M sodium sulfite.
About 1.2 grams (g) of the raw acrolein was accurately
weighed into the flask with a weighing pipet. The flask was
tightly stoppered and shaken for 5 minutes to complete the
reaction of acrolein with the bisulfite. The unreacted
bisulfite was potentiometrically titrated with standard 1
normal (N) sodium hydroxide. The end point, found in these
studies, appeared at pH 9.5. Potentiometric titration and
use of equation (1) revealed that one bisulfite molecule
formed a complex with each molecule of acrolein. This
information and the end point are not given in the
literature.22/23 The percentage of acrolein was calculated
according to
(Vi - V2) x N x 56.06
Acrolein, % = .
W x 10
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where V = standard 1 N sodium hydroxide required to
titrate 50.0 ml of standard 1 N sulfuric acid
in the excess sulfite (milliliters)
V = standard 1 N sodium hydroxide used to titrate
the sample (milliliters)
N = normality of standard 1 N sodium hydroxide
W = weight of acrolein taken for analysis (grams}
Reagent-grade acrolein was cloudy and contained about 65%
acrolein by bisulfite assay, whereas the freshly distilled
product inhibited with 0.1% w/v hydroquinone contained about
93% acrolein and was clear. Assay results are presented in
table 1.
TABLE 1. BISULFITE ASSAY RESULTS FOR ACROLEIN
Source
Eastman (distilled)
Eastman (as received)
Baker (as received)
Appearance
Clear
Cloudy
Cloudy
Acrolein content, %
92.7 (average of 3 tests)
67.7
64.9
Acrolein was also assayed by an infrared technique29 based
on the relative absorbances of bands attributable to the
acrolein dimer (2-formyl-3,4-dihydro-2H-pyran) : an ortho-
substituted phenyl band at 13.6 ym and an ether band at
9.35 vim. The infrared assay revealed that the acrolein as
received contained about four times more total impurities,
mainly the dimer (also called disacryl), than the freshly
distilled product, thereby confirming the bisulfite assay.
Infrared spectra indicated that the unidentified precipitate
found in the acrolein as received contained little, if any,
disacryl. This suggests that the dimer is a soluble
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material that gradually forms even in freshly distilled
acrolein.
Another method for assaying acrolein was suggested by
James.30 This method is based on brominating the double bond
in acrolein and titrating the excess bromine with standard
thiosulfate. Had this method been used, it would have
indicated higher concentrations of acrolein than were
actually present because of interference from disacryl,
which has a double bond that consumes bromine. On the other
hand, the formyl group in disacryl probably does not
interfere in the bisulfite assay because it is chemically
similar to furfural, which is known not to interfere.23
Acrolein Stock Solution
To prepare a stock solution of acrolein, about 1 g of
purified acrolein (weighed to the nearest 0.01 g) was
dispensed from a weighing pipet into reagent water in a
1000-ml volumetric flask. The solution was diluted to 1
liter (1). The concentration of acrolein in the stock
solution was calculated in milligrams per milliliter, taking
into consideration the acrolein content found by bisulfite
assay. This solution must be prepared fresh daily.
Acrolein Standard Solution
A standard solution of acrolein was prepared by appropriate
dilution of the stock solution to 100 mg/1.
Phosphate Buffer Solution
The 1.0 M phosphate buffer solution, pH 7.4, was prepared by
mixing 300 ml of 1.0 M dipotassium hydrogenphosphate
(174.18 g/1) and 100 ml of 1.0 M potassium
dihydrogenphosphate (136,09 g/1). Table 2 gives the
preparation of phosphate buffer solutions used to test the
effects of pH on the polarographic behavior of acrolein.
EDTA Solution
A 10% (w/v) EDTA solution was prepared by dissolving 25 g of
disodium ethylenediaminetetracetic acid dihydrate and
diluting to 250 ml with reagent water. Dissolution was
completed by magnetically stirring the solution while
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TABLE 2. PREPARATION OF PHOSPHATE BUFFER SOLUTIONS
FOR TESTS OF THE EFFECTS OF pH ON POLAROGRAPHIC
DETERMINATION OF ACROLEIN
pH Of 10.0 ml Of
Water with 0.5 mg/1
Combined pH of Acrolein and 100^1
Phosphate (KH PO ) ,ml Mixed or Unmixed of 10% EDTA in 1.0
pH 4.2 pH 9.3 Phosphate Buffer ml of Phosphate Buffer
0
2.5
5.0
10.0
X
X
17.5
15.0
10.0
0
9.3
7.8
7.4
6.7
4.2
8.3
7.6
7.2
6.8
4.3
heating it in a hot water bath. After a Whatman No. 30
filter pater was rinsed with two 25-ml aliquots of reagent
water, two 5-ml aliquots of the solution were filtered
through it and discarded, and the remaining solution was
filtered and saved.
Sodium Sulfite Solution
A 1-M sodium sulfite stock solution was prepared by
dissolving 255.935 g of 98.5% sodium sulfite (NaaSOs) in
reagent water and diluting to 2000 ml. A 17.85-ml aliquot
of this solution was diluted to 100 ml to yield a
22,500-mg/1 solution. This solution was diluted further to
give a 225-mg/l solution, 1 ml of which is equivalent to
100 lag of acrolein because, as found by bisulfite assay, one
molecule of sodium sulfite forms a complex with each
molecule of acrolein.
10
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PROCEDURE
Voltammetry at Negative Potentials with the Dropping
Mercury Electrode (Polaroqraphy)
For these studies, the PAR polarographic analyzer was
adjusted as follows: drop time, 2 seconds; scan rate, 2
millivolts per second (mV/sec); display direction, positive;
scan direction, negative; initial potential, -0.900 or
-0.500 volt (V); range, 1.5 V; modulation amplitude, 100 mV;
operation mode, differential pulse. The Y-axis of the
recorder was set at 1 volt per inch (V/in., 0.039 volts per
millimeter, V/mm) to provide 10 V full scale, and the X-axis
was set at 100 mV/in. (3.94 mV/mm) to provide a range of 1.5
V. The voltage output offset was adjusted negatively, as
necessary, to bring the recorder pen on scale, and the
microamperage switch was adjusted to values between 0.2 and
2 microamperes (yA) full scale depending on the
concentration of acrolein.
The counter electrode was spectroscopic-grade grapnite. The
reference electrode, a calomel electrode filled with
saturated sodium chloride, was isolated from the test
solution by a slow-leakage sintered-glass frit in a salt
bridge, which contained the same electrolyte as the test
solution. Without a salt bridge, a moderately sloping
cathodic background made the measurement of the peak heights
formed by reduction of the acrolein inexact.
The test solutions consisted of 10.0 ml of the standard or
sample to be analyzed; 1.00 ml of phosphate buffer solution
(pH 7.4) or other ingredients, such as sulfite, as
specified; and 100 microliters (yl) of 10* EDTA solution.
The mixture was dispensed immediately into a polarographic
cell (5-to 50-ml capacity). The mercury head above the
capillary was adjusted to about 45 centimeters (cm) to
produce a natural drop time of about 3 seconds in the test
solution. The test solutions were deaerated 10 minutes
(min) with purified nitrogen. After deaeration, the test
solution was electrically connected and allowed to quiesce
for about a minute. For best sensitivity it was absolutely
necessary to remove all traces of oxygen from the gas used
to sparge the test solution.
11
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Voltammetry at Positive Potentials with the Glassy
Carbon Electrode
The instrumental parameters for these studies were similar
to those for voltammetry at negative potentials with the
dropping mercury electrode except that the initial
potentials were -0.200 V, the voltammograms scanned
positively, and the peaks displayed negatively. The voltage
output offset was adjusted negatively, as necessary, to
bring the recorder pen on scale, and the milliamperage
switch was adjusted, as necessary, to 0.1, 0.2, or 0.5
milliampere {mA) full scale. Voltage scans were usually
terminated at about +1.1 V because the background current of
the electrolyte itself obscured the voltammogram.
The reference and counter electrodes were those described in
the preceding section. The reference electrode was placed
directly in the test solution; a salt bridge was not
necessary under these conditions. Before each run, the
glassy carbon electrode was cleaned for 1 min at +1.0 V vs.
S.C.E. (NaCl). This greatly reduced the current background
from the electrode itself between -0.2 and +1.1V. After it
was cleaned, the electrode was rinsed with reagent water,
wiped with a tissue, and rinsed again.
The test solutions are described in the "Results and
Discussion" section.
Preservation with Sulfite
In these studies, acrolein solutions were treated with
either an excess of sodium sulfite or the chemically
equivalent amount. Polarographic measurements were made
using the same cell, electrodes, salt bridge, and instrument
settings specified in the "Voltammetry at Negative
Potentials with the Dropping Mercury Electrode
(Polarography)" section, except that the initial voltage
settings were changed as mentioned in the "Results and
Discussion" section.
The test solutions are described in the Results and
Discussion section.
12
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SECTION V
RESULTS AND DISCUSSION
VOLTAMMETRY AT NEGATIVE POTENTIALS WITH THE DROPPING
MERCURY ELECTRODE (POLAROGRAPHY)
Experimentation led to the development of a sensitive
differential pulse polarographic method for determining
concentrations of acrolein in water. In brief, the method
involves adding 1.00 ml of 1.0 M phosphate buffer solution
and 100 ul of 10% EDTA solution to 10.0 ml of sample,
removing dissolved oxygen by sparging with nitrogen for
10 min, and recording the polarogram. The height of the
acrolein reduction peak at -1.22 V vs. S.C.E. (NaCl) is
measured, and the acrolein concentration is determined from
a standard curve prepared by polarographing a series of
standard acrolein solutions. The recommended procedure is
given in the appendix.
The detection limit of the method was found to be 0.05 mg/1,
approximately 20 times the sensitivity obtained by direct-
current polarography.*o The concentration range extends to,
or beyond, 0.5 mg/1, the highest level used in determining
acrolein demand. With the mercury electrode adjusted to
provide a natural drop time of 2.7 seconds in 0.09 M
phosphate, standard solutions containing 0.1, 0.3, and
0.5 mg/1 of acrolein produced peak currents of 112, 392, and
630 nanoamperes (nA), respectively. No measureable current
was observed for a reagent blank. The standard curve
produced from these readings is displayed in figure 1. The
corresponding- polarograms are presented in figure 2.
The precision and accuracy of the recommended method were
based on seven replicate analyses of freshly prepared
standard solutions containing 0.10 and 0.30 mg/1 of
acrolein. The standard deviations were 0.008 and
0.013 mg/1, respectively, and the relative standard
deviations were 7.1 and 4.3 %. The standard deviation was
13
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700
600
0
O.I
0.2 0.3
ACROLEIN, mg/l
0.4
0.5
Figure 1. Calibration Curve for Acrolein
-------
O.lmg/l
ACROLEIN
lOOnA
0.3mg/l
ACROLEIN
0.5mg/l ACROLEIN
{ lOOnA
-0.9 -1.0 -I.I -1.2 -1.3 -1.4 -1.5
VOLTS vs S.C.E. (NaCI)
-1.6
Figure 2. Polarograms for Acrolein with Dropping
Mercury Electrode
15
-------
computed using n-1 for weighting, where n is trie number of
observations. Recoveries (means of seven determinations) of
0.10 and 0.30 mg/1 acrolein were 97 and 97 %, respectively,
corresponding to relative errors of 2.9 and 3.3 £.
The polarographic method was compared with the colorimetric
method for determining the acrolein demand of samples of
water taken in the Tennessee Valley. The colorimetric
method is the Betz Laboratories test method* with spectro-
metric determination of absorbance at 600 nanometers (nm).5
Acrolein demand, which is analogous to chlorine demand,31 is
the difference between the concentration of acrolein added
(usually 0.30 mg/1) and that found after a 1-hour test
period. Analytical results for acrolein demand after one
hour for split samples of surface waters with 0.3 mg/1
acrolein added and analyzed by the polarographic and
colorimetric methods are given in table 3. According to the
paired-sample t test,32 the mean of the differences (d)
between these observations is not significantly different
from zero at the 0.05 level of significance. The t values
were calculated by multiplying the mean of the differences
by the square root of the paired observations and dividing
by the standard deviation for the differences. The standard
deviation was computed using n-1 weighting, where n is the
number of observations. The t value was 1.30, which is less
than that of 1.75 given for t0.os f°r 15 degrees of freedom
in the t table.32 Thus, at the 6.05 level there is only one
chance in 10 of incorrectly concluding tnat the methods do
not differ. Acrolein demand at 0.10- and 0.50-mg/l
concentrations was determined by both the colorimetric and
polarographic methods. Approximately the same fraction of
acrolein was consumed at these levels as at 0.30 mg/1.
Chemical Interferences
Zinc -
Zinc interfered in the polarographic determination of
acrolein in the 0.09 M phosphate buffer solution (pH 7.4) by
causing a high current at -1.22 V vs. S.C.E. (NaCl). The
background current in samples that contained 2.0 mg/1 of
zinc was about four times that for 0.5 mg/1 of acrolein.
This is important because many natural waters contain as
much as 2.0 mg/1 zinc. However, the interference of
2.0 mg/1 of zinc was completely eliminated by the addition
of 0.09% EDTA in the electrolyte. It is well known that 3%
EDTA eliminates electrochemical interference by zinc.33
However, it was not known that lower concentrations of EDTA
16
-------
TABLE 3. COMPARATIVE TEST RESULTS FOR ACROLEIN DEMAND
AFTER HOUR FOR SPLIT SAMPLES OF SURFACE WATERS
WITH 0.30 mg/1 ACROLEIN ADDED
Acrolein demand, mg/1
Location Polarographic Colorimetric
Duck River Mile 133.92
Duck River Mile 156.51
Duck River Mile 64.0
Duck River Mile 47.9
Holston River Mile 131.5
Holston River Mile 118.4
Paradise Tower Inlet
Paradise Tower Outlet
Holston River Mile 118.4
Holston River Mile 131.5
French Broad River Mile 54.3
French Broad River Mile 77. 5
French Broad River Mile 71.4
Nolichucky River Mile 5.3
Cumberland River Mile 285
Tennessee River Mile 391.2
0.09
0.13
0.11
0.08
0.08
0.08
0.15
0.09
0.13
0.13
0.16
0.10
0.12
0.07
0.07
0.11
0.11
0.03
0.01
0.07
0.11
0.14
0.10
0.16
0.15
0.09
0.12
0.06
0.14
0.09
0.01
0.03
The Paradise Tower is located along the Green River, which
discharges into the Ohio River.
17
-------
could be used in high-sensitivity polarography for the dual
purpose of eliminating interference by zinc and contaminants
in the EDTA itself.
Other Elements -
Other elements besides zinc might interfere in the
determination of acrolein. These may appear in the
polarogram as a peak at a voltage near that for acrolein or
as a cathodic background with a positive or negative slope.
If this should occur, the amperage peak for a blank of raw
sample water may be determined and subtracted from that for
the sample with added acrolein. This correction can be more
precisely performed digitally with a microprocessor-
controlled polarograph (Princeton Applied Research Model 374
Polarographic Analyzer System). In these studies, this was
not necessary for the more than 50 samples taken throughout
the TVA water system and analyzed by the recommended method.
If the background should be such that the current for the
blank is much greater than that for acrolein, the acrolein
can be separated by distillation,4 and the distillate can be
analyzed polarographically by the recommended method. In
one test of the distillation procedure, we sparged nitrogen
at 100 ml/min for 20 min through a synthetic sample heated
in a boiling water bath, trapped the acrolein released in
20 ml of reagent water instead of colorimetric reagent,* and
analyzed the distillate polarographically. The
concentration of acrolein in the distillate was about 2-1/2
times that in the original sairple. We expected a 5-fold
increase from the ratio of sample volume to distillate
volume. Specifically, when 0.50 mg/1 acrolein in 100 ml of
reagent water was distilled with nitrogen, 46% of the
acrolein was found in the 20 ml of distillate, 6% remained
in the residue, and by difference 48J& was lost, presumably
by polymerization or to the atmosphere. Van Sandt10 found
approximately the same loss when acrolein was collected on
silica gel and eluted for polarographic analysis. It should
be noted that distillation concentrates the sample and
thereby decreases the detection limit at least 2-1/2 fold.
p_K -
The pH of the test solution affects botn peak height and
potential. The optimum pH is 7.2. Tests were conducted at
22°C with 0.50 mg/1 acrolein solutions at pH 4.3, 6.8, 7.2,
7.6, and 8.3, buffered with phosphate solutions (0.09 M)
18
-------
with 0.09* EDTA added (table 2). The height and potential
of the acxolein reduction peak were the same at pH 6.8, 7.2,
and 7.6. The pH of most water samples can be adjusted and
maintained at pH values between 6.8 and 7.6 by the addition
of 1.0 ml of 1.0 M phosphate buffer solution (pH 7.4) and
100 yl of 10* EDTA solution to a 10.0 ml sample. Adjustment
may be required for strongly acidic samples, such as
drainage irom strip mines.
At pH 4.3 the peak height for 0.50 mg/1 acrolein was 45% of
the value at pH 7.2, and the potential was -1.10 V vs.
S.C.E. (NaCl) rather than -1.22 V. These shifts of peak
potential and peak height found by differential pulse
polarography agree with Moshier's observations by direct
current polarography.9 At pH 8.3, the peak height did not
change appreciably, but the potential shifts to -1.25 V.
The addition of bisulfite to the carbonyl group in acrolein
destroyed the peak but so did hydrogenation of the double
bond--propionaldehyde is not polarographically active at
voltages less than -1.4 V vs. S.C.E. The direct current
polarographic reduction wave for propionaldehyde in 0.1 M
lithium hydroxide did not appear until about -1.9 V.ia The
absence of differential pulse polarographic activity between
-0.5 and -1.4V was observed for the acrolein-bisulfite
complex in a test solution that was deaerated for 10 min
and consisted of 10 ml of 0.50 mg/1 of acrolein, 22.5 mg/1
of sodium sulfite (sufficient to form the complex with 10
mg/1 of acrolein), 1.0 ml of 1.0 M phosphate buffer solution
(pH 7.4) and 100 yl of 10% EDTA solution. Since neither the
double bond in the acrolein-bisulfite complex nor the
carbonyl in propionaldehyde are polarographically active in
the -0.5-V to -1.4-V range, then the ir-electron system,
which includes both, must be involved in the reduction of
acrolein. But these observations do not contradict that the
reduction may be represented by the equations
CH5=CH - CHO + 2H+ + 2e »CH -CH9-CHO (2)
CH5=CH - CHO + 4H* + 4e ^ CH -CH^-CIL, OH (3)
Equation (2) represents the first peak, which is given by
figure 1, and equation (3) represents the second peak.
19
-------
Oxygen -
Dissolved oxygen greatly reduces the sensitivity attainable
by differential pulse polarography. For best sensitivity it
is absolutely necessary to remove traces of oxygen from the
test solution and from the nitrogen used to sparge the
solution. The gas system must te purged overnight before
commencing analysis. We conducted experiments to determine
the optimum outgassing time and found that 10 min produced
the best sensitivity. The reference electrode must be
isolated by a salt bridge from the solution being measured
to eliminate sloping baselines caused by oxygen entry,
leakage of salt solution from the reference electrode, or
both.
Physical Interferences
Decomposition -
In the polarographic determination of acrolein, peak heights
decreased by about 10% on the second polarographic scan.
For best results, each operator should carefully reproduce
the outgassing period and the quiescent time before
beginning each scan.
Instrumentation -
Instrument settings greatly affect the sensitivity16 of
differential pulse polarography. The drop time, the pulse
modulation amplitude, and even the scan rate change the
height of the peak.
VOLTAMMETKY AT POSITIVE POTENTIALS WITH THE GLASSY
CARBON ELEC1RODE
Several experiments were conducted to develop a method for
analyzing acrolein by voltammetry at positive potentials
using the glassy carbon electrode. Glassy carbon, a
recently developed electrode material,3* is available in
electrode form from Princeton Applied Research
Corporation.19 Operating at positive potentials usually
requires no deaeration, as opposed to the lengthy deaeration
needed at negative potentials.18
Experimentation led to an indirect determination of acrolein
by formation of the acrolein-sulfite complex and
20
-------
voltammetrie measurement of unreacted sulfite at about
+0.6 V vs. S.C.E. (Nad) with the glassy carbon electrode
(see figure 3). The electrolyte is buffered at pH 7.2 with
0.09 M phosphate. Lengthy deaeration is unnecessary, but
the detection limit is only 10 mg/1 (as compared to
0.05 mg/1 with the polarographic method).
Before each of the experiments discussed below, the glassy
carbon electrode was cleaned as described in the "Procedure"
section. The instrument settings are also given in the
"Procedure" section. The first experiments were performed
to determine whether acrolein would oxidize in the voltage
range from -0.2 V to about +1.2 V. A series of test
solutions consisted of 10.0 ml of a 100-mg/l standard
acrolein solution plus 1.00 ml of either 1.0 M phosphate
buffer solution (pH 7.U), 1.0 N sodium hydroxide, or 1.0 N
sulfuric acid. The test solutions were sparged with
nitrogen for 10 min before a slow voltammetric scan was
begun in the differential pulse mode at -0.2 V vs. S.C.E.
(Nad) and 100^A full scale.
No polarographic peaks were otserved between -0.2 and
+ 1.1 V vs. S.C.E. (NaCl) for any of the solutions. Because
acrolein seemed to be inactive over the wide range of pH
values examined, further testing was abandoned.
Acrolein readily forms a sulfite complex,lr 22 as seen in
equations (4) and (5). 2 3
0 H
n i
H2C = CH-C-H + NaHS03-»- H2C = CH-C-OH (4)
S03Na
0 H
H2C=CH-C-H + Na2 S03 + H20 -*- H2C=CH-C-OH + NaOH (5)
S03Na
This suggests the basis for a determination of acrolein
either directly in the form of the complex or indirectly by
measurement of the unreacted sulfite. Equations (U) and (5)
were derived from the general reactions of sulfite forms
with aldehydes and from our finding, discussed in the
experimental section, that one sulfite molecule reacts with
21
-------
NJ
C
It
fP
Q <
H O
ju ^
0) ft
cn (u
*< 3
O O
cr a)
O 3
O
W M>
(-•
(D cn
O (=
ft M
K l-h
O H-
O> ft
(D m
ft)
ft
a
c
H-
ft
tr
-0.2
0.2 0.4 0.6
VOLTS vs S.C.E. (NaCI)
0.8
1.0
1.2
-------
one molecule of acrolein. Because acrolein can react with
sodium sulfite or sodium bisulfite, either form of sulfite
can be used in studying the reaction. The ionization
constants35 of sulfite are such that the chemical forms
change, with sulfur dioxide predominating at pH 1, bisulfite
at pH 4, and sulfite in neutral and alkaline solutions.
Exploratory studies were conducted on the voltammetry of
sodium sulfite alone and in the presence of acrolein. The
study was conducted with the glassy carbon electrode at
pH 1, 4, 7, and 13. The first experiment was made on a test
solution consisting of 10.0 ml of 225 mg/1 of sodium sulfite
and 1.00 ml of 1.0 M phosphate buffer solution (pH 7.4).
The solution was sparged for 10 min. The voltammogram,
shown in figure 3, exhibited a large peak at
+0.58 V vs. S.C.E. (Nad), which is approximately the
potential predicted from the standard potential.21 The peak
height was 146 yA. In contrast, there was no peak on the
voltammogram of a test solution containing 225 mg/1 of
sodium sulfite and 100 mg/1 acrolein, an amount stoicnio-
metrically equivalent to the amount of sulfite. This
indicated that the sulfite reacted quantitatively with
acrolein to form a polarographically inactive complex.
When the deaeration time was decreased from 10 min to 5, 2,
and 1 min, the peak current decreased to 134, 137, and
137 yA, respectively. With no deaeration, it was 100 yA.
The slope of the background current did not change
appreciably as the deaeration time was decreased. Because
the peak heights were essentially unaffected by additional
deaeration, subsequent experiments on sulfite were conducted
with 1 min of outgassing.
The voltammogram of a test solution containing 10.0 ml of
225 mg/1 of sodium sulfite and 1.00 ml of 1.0 N sodium
hydroxide exhibited a peak at +0.59 V vs. S.C.E. (NaCl), see
figure 4. The peak height of 136 yA approximately equaled
that found at the neutral pH of the 0.09 M phosphate buffer
solution. In contrast, the addition of 100 mg/1 of acrolein
resulted in a peak current of only 7 yA at +0.59 V. This
indicated that the acrolein-sulfite complex is not
decomposed in dilute alkali, at least not at this
concentration (91 mg/1, when dilution with the sodium
hydroxide is considered).
The next set of experiments was the same as the previous one
except that 1.00 ml of 1.0 M phosphate buffer solution
(pH 4.2) was added instead of the sodium hydroxide. Under
these conditions, however, the sulfite peak—or, more
23
-------
to
f:
H-
C
ft)
-t
€ <
H- O
ft I-
tr ft
ft)
CD 3
I-- 3
0) O
0) iQ
CO H
k< (li
o3
ft) O
l-t Hi
cr
o en
3 n
M
M H,
»-• M-
(D ft
o n
O ft
a
05 t)
03
50//A
225mg/l Na2S03
I
I
-0.2
0.2 0.4 0.6
VOLTS vs S.C.E. (NaCI)
0.8
-------
correctly, the bisulfite peak, which predominates at
pH 435—appeared at +0.79 V, +0.21 V more positive than at
pH 7.4 (see figure 5). The peak height for sulfite alone
was 152 yA. As at pH 7.4, the sulfite peak was nearly
eliminated in the presence of an equivalent amount of
acrolein. The stoichicmetric quantity of acrolein decreased
the height of the sulfite peak to 7 yA.
In the final experiment, 1.00 ml of 1.0 N sulfuric acid was
added to 10.0 ml of a 225 mg/1 sulfite solution. A peak for
sulfurous acid, the conjugate acid form of sulfite, appeared
at +1.06 V (see figure 6). The height of this peak was
196 yA. The stoichiometric amount of acrolein did not
eliminate this peak; the peak decreased slightly to 183 yA.
These experiments showed that sulfite quantitatively or
nearly quantitatively reacted to form a complex with
acrolein between pH 4 and pH 13. The complex decomposes,
almost quantitatively, at about pH 1. Both acidic and basic
solutions gave polarograms with steeply sloping baselines.
The best polarograms with the best baselines were obtained
in solutions buffered with 0.09 M phosphate at pH 7.4 (see
figures 3-6}.
Because the neutral phosphate system was the best for
measuring acrolein by determining unreacted sulfite, we
decided to determine the detection limit. The detection
limit is about 10 mg/1 acrolein, which is equivalent to
22.5 mg/1 of sodium sulfite. The peak height for 22.5 mg/1
of sodium sulfite was approximately 6 yA. The sensitivity
might be improved with the graphite electrode impregnated
with styrene and irradiated with cobalt 60.36
Formation of the acrolein-sulfite complex might be effective
for neutralizing the toxicity cf acrolein. It is thought
that the complex is not toxic.*
Voltammetric oxidation of sulfite at the glassy carbon
electrode in neutral solutions may be applicable to
monitoring sulfur dioxide in air. The detection limit of
22.5 mg/1 for sodium sulfite achievable by this method
corresponds to 11.4 mg/1 of sulfur dioxide. If the sulfur
dioxide in a 100-liter sample of air were trapped with 100%
efficiency in 1.00 ml of buffered electrolyte, this
represents a concentration of 0.044 yl/1 (25 °C, 760 mm Hg
at 0 °C, 1.013x105 pascal, Pa) of sulfur dioxide.
25
-------
50//A
225mg/l Na2S03
I
-0.2
0.2 0.4 0.6 0.8
VOLTS vs S.C.E. (NaCI)
l.O
1.2
Figure 5. Voltammogram of Sulfite at pH
with Glassy Carbon Electrode
-------
to
-J
225mg/l Na2S03
-0.2
0.2
0.4 0.6 0.8
VOLTS vs S.C.E. (NaCI)
i.O
1.2
Figure 6. Voltammogram of Sulfite at pH 1
with Glassy Carbon Electrode
-------
PRESERVATION WITH SULFITE
The purpose of these studies was to develop a technique for
preserving water samples for several days while they are
shipped to the laboratory for analysis of low levels of
acrolein. While high levels of acrolein, 2-8 mg/1, can be
preserved with excess sulfite,28 there was no information on
low-level preservation or analysis of acrolein in concentra-
tions of 0.05-0.5 mg/1 with excess sulfite added.
Initial efforts were toward a direct measurement of acrolein
released from its complex with sulfite. Because voltammetry
at the glassy carbon electrode is not sensitive enough to
measure acrolein at the 0.5 mg/1 level and below, the
polarographic procedure (voltammetric procedure at the
dropping mercury electrode) was modified in attempts to find
suitable conditions for a direct analysis. No entirely
adequate polarographic method was found for analyzing low
concentrations of acrolein in the presence of excess sulfite
through the experiments described below.
All of the polarographic scans in the following experiments
were conducted under nearly the same conditions as those in
the recommended method with the exception that, in some
instances, the initial voltage was changed to assure that no
polarographic peaks were missed.
The first experiment was performed on a test solution
consisting of 0.5 mg/1 of acrolein, 22.5 mg/1 of sodium
sulfite (sufficient to form the complex with 10 mg/1 of
acrolein), 1.00 ml of 1.0 M phosphate buffer solution
(pH 7.4), and 100 yl of 10* EDTA solution. After the sample
was deaerated for 10 min, the polarogram was recorded
beginning at -0.500 V. No significant polarographic peaks
appeared between -0.5 and -1.4 V, and it was concluded that
the acrolein-sulfite complex is not polarographically active
at pH 7.4.
This experiment was repeated with 1.00 ml of 1.0 M sodium
hydroxide in place of the phosphate buffer. No
polarographically active peaks were observed between -0.9
and -1.55 V.
With 1.00 ml of 1.0 N sulfuric acid substituted for the
sodium hydroxide, a peak for acrolein was observed at
-0.88 V. The peak height was 344 nA (see figure 7). The
height was very difficult to measure because the baseline
sloped considerably and increased rapidly at about -1V. In
a fourth test solution containing no sodium sulfite, the
28
-------
_ t
lOOnA
22.5mg/l Na2S03 +
0.5mg/l ACROLEIN
1
-0.5
-0.6 -0.7 -0.8 -0.9
VOLTS vs S.C.E. (NaCl)
-1.0
Figure 7. Polarogram for Acrolein in Excess Sulfite
at pH 1 with Dropping Mercury Electrode
29
-------
peak current for acrolein was 592 nA (see figure 8).
However, the baseline still sloped considerably and
increased rapidly at about -1V. Because of the unfavorable
baseline ph (the most favorable at the time) , this technique
was unsatisfactory for measuring acrolein at the 0.5 mg/1
level. Had a microprocessor (Princeton Applied Research
Model 374 Polarographic Analyzer System) been available to
correct digitally for the steeply sloping baseline caused by
the sulfuric acid blank, this electrolyte might well have
been suitable for precisely determining acrolein in samples
preserved with sulfite.
Because a polarographic peak was observed for 0.5 mg/1 of
acrolein in dilute sulfuric acid in the presence of a
20-fold excess of sodium sulfite, sulfite might be converted
to sulfur dioxide in dilute acid and removed by sparging
with argon, allowing the determination of the regenerated
acrolein at neutral pH with the recommended polarographic
method.
To test this approach, a synthetic solution was prepared to
simulate a water sample preserved for acrolein analysis. To
100 ml of reagent water was added enough acrolein to produce
a concentration of 0.5 mg/1, enough sodium sulfite to
produce a concentration of 22.5 mg/1, and 1.00 ml of 1.0 M
phosphate buffer solution (pH 7.4). There was enough
sulfite present to form a complex with 10 mg/1 of acrolein.
The addition of 3.0 ml of 1.0 N sulfuric acxd lowered the pH
of this solution from about 7.2 to 2.1. Argon (presaturated
with water), delivered vigorously through a coarse, sintered
glass frit, was used to deaerate the solution for various
lengths of time. The amount of acrolein in the solution was
determined by the recommended procedure. Low recovery rates
resulted, even after the optimum outgassing time of 20 min.
At most, only 15% of the acrolein was recovered. Therefore,
this approach was abandoned.
The last approach was an attempt to release acrolein from
the sulfite complex by distillation from an alkaline
solution. To 100 ml of a solution containing 0.5 mg/1 of
acrolein, 22.5 mg/1 of sodium sulfite, and 1.0 ml of
phosphate buffer solution (pH 7.4) was added 10 ml of 1.0 N
sodium hydroxide. In a closed system, the entire solution
was heated in a boiling-water bath while being sparged with
argon. The gas from the system was scrubbed through a 10-ml
impinger with a sintered glass disc at the inlet. The
impinger contained 10 ml of reagent water, 1.0 ml of 1.0 M
phosphate buffer (pH 7.4), and 100 ul of 10* EDTA solution.
After 20 min of sparging, the solution in the impinger was
30
-------
O.Smg/l ACROLEIN
_ t
lOOnA
-0.5 -0.6 -0.7 -0.8 -0.9 -1.0
VOLTS vs S.C.E. (NaCI)
Figure 8. Polarogram for Acrolein at pH 1 with
Dropping Mercury Electrode
31
-------
analyzed for acrolein by the recommended procedure. About
11% of the acrolein was recovered in this attempt to release
the acrolein from the bisulfite complex.
Sulfite may very well be an effective preservative for low
concentrations of acrolein in water samples, but no method
was found to find a way to recover acrolein from solutions
containing sulfite.
32
-------
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p. 5-150-5-151.
21. Lingane, J. J. Electroanalytical Chemistry. Second
Edition. New York, Interscience Publishers, July 1970.
p. 546-548, 649.
22. Beilstein. Handbuch der organischen Chemie. (Handbook
of Organic Chemistry). Volume 1, Second Supplement.
Berlin, Julius Springer, 1941. p. 782-786.
23. Siggia, S. Quantitative Organic Analysis via Functional
Groups. Third Edition. New York, John Wiley 6 Sons,
1963. p. 79-85.
24. Nadar, John S. Direct Reading Instruments tor Analyzing
Gases and Vapors. In: Air Sampling Instruments.
Fourth Edition. Cincinatti; American Conference of
Governmental Industrial Hygienists, 1972. p. U-5, -6,
-31, -34, -39, -48.
25. Purdue, L. J. Performance of SO Monitoring
Instruments. In: Instrumentation for Monitoring Air
Quality, Barras, R. C. (symposium chairman).
Philadelphia, ASTM Special Technical Publication 555,
1974. p. 6-7, 12-13.
26. Garber, R. W. and C. E. Wilson. Determination of
Atmospheric Sulfur Dioxide by Differential Pulse
Polarography. Anal. Chem. 44(8);1357-1360, July 1972.
27. Jackson, Elliot. Personal Communication on Preserving
Acrolein with Sulfite. Betz Laboratories, Inc.,
Trevose, Penna. May 28, 1975.
28. Smith, R. G., Bryan, R. J., Feldstein, M., Locke, D. C.
and Warner, P. O. Tentative Method of Analysis for
Formaldehyde, Acrolein, and Low Molecular Weight Alde-
35
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hydes in Industrial Emissions on a Single Collection
Sample. Health Laboratory Science. 12 (2):164-166,
April 1975.
29. Quigley, W. J. Personal Communication on Infrared Tests
on Acrolein. TVA Central Laboratories, Power Service
Center, Chattanooga, Tenn. May 1974.
30. James, E. W. Personal Communication on Assaying
Acrolein in Slimicide C-20. Betz Laboratories, Inc.,
Trevose, Penna. March 26, 1974.
31. Sawyer, C. N. and P. L. Mccarty. Chemistry for
Sanitary Engineers. Second Edition. New York, McGraw-
Hill Publishers, 1967. p. 374.
32. Miller, I. and J. E. Freund. Probability and
Statistics for Engineers. Prentice-Hall, Inc.,
Publishers, 1965. p. 169-170, 399.
33. American Public Health Assoc. Standard Methods for the
Examination of Water and Waste Water. 13th Edition.
New York, American Public Health Assoc., Publishers,
1971. p. 448-451.
34. Florence, T. M. Anodic Stripping Voltammetry with a
Glassy Carbon Electrode Mercury-Plated in situ.
Electronal. Chem. .27:273-281, 1970.
35. Sillen, L. G. and A. E. Martell. Stability Constants
of Metal-Ion Complexes. Special Publication No. 17.
London, The Chemical Society, Burlington House, W.1,
Publishers, 1964. p. 229-230.
36. Clem, E. G. and A. F. Sciamanna. Styrene Impregnated,
Cobalt-60 Irradiated, Graphite Electrode for Anodic
Stripping Analysis. Anal. Chem. _47:276-280, February
1975.
36
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LIST OF PUBLICATIONS
"Differential Pulse Folarographic Determination of Acrolein
in Water Samples" ty Lyman H. Kowe was accepted on September
3, 1976, by Analytical Chemistry for tentative publication
in December of 1976.
37
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GLOSSARY
Acrolein demand - Quantity of acrolein dissipated
in the test water.
A - Ampere.
c- - Centi-, X10-* (as a prefix, e.g., cm).
cl - Mean of the differences between paired
observations.
°C - Degrees Celsius (centigrade).
EDTA - Ethylenediaminetetraacetic acid.
3 - Grams.
hr - Hour.
1 - Liter.
m - Meter.
jj^. ~ Micro-, X10-* (as a prefix, e.g., 1).
m- - Milli-, X10~3 (as a prefix, e.g., mm).
min - Minute.
M - Molar, mole per liter.
n- - Nano-, X10~9 (as a prefix, e.g., ng).
N - Normal, equivalent per liter.
% - Percent.
38
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Pa. - Pascal.
Polaroqraphy - Voltammetry at the dropping
mercury electrode.
PAR - Princeton Applied Research.
t - Student-t statistic.
TVA - Tennessee Valley Authority.
V - Volt.
V vs. S.C.E^ - Volts versus a calomel electrode filled
with saturated potassium chloride.
V vs. S.C..E. (NaCl) - Volts versus a calomel electrode
filled with saturated sodium chloride.
w/v - Weight expressed as a fraction of total volume.
39
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APPENDIX
RECOMMENDED POLAROGRAPHIC PROCEDURE (VOLTAMMETRIC
PROCEDURE AT DROPFING-MERCURY ELECTRODE)
FOR ACROLEIN ANALYSIS
REAGENTS
Acrolein Stock Solution
With a weighing pipet, transfer about 1 g of purified
acrolein (weighed to the nearest 0.01 mg) to a 1000-ml
volumetric flask containing 500 ml of reagent water. Dilute
the solution to 1000 ml and mix. Prepare a fresh solution
daily.
Acrolein Standard Solution, 100 mq/1
Prepare this solution by appropriate dilution of the stock
solution.
Phosphate Buffer Solution, pH 7.4
Solution A—Dissolve 174.18 g of dipotassium hydrogen-
phosphate in reagent water and dilute, to 1000 ml. This
1.0 M solution has a pH of 9.3.
Solution E—Dissolve 136.09 g of potassium dihydrogen-
phosphate in reagent water and dilute to 1000 ml. This
1.0 M solution has a pH of 4.2.
Phosphate buffer solution, pH 7.4—Mix 300 ml of solution A
with 100 ml of solution B.
40
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EDTA Solution, 10% (w/v)
Dissolve 25 g of disodium ethylenediaminetetraacetic acid
dihydrate and dilute to 250 ml with reagent water. Heat and
stir the solution if necessary to complete dissolution of
the salt. If dissolution is incomplete, filter the
solution, and discard the first 10 ml.
INSTRUMENTAL
The natural drop time of the capillary should be approxi-
mately 3 sec in 0.09 M phosphate buffer solution (pH 7.4).
Use a carbon or platinum counter electrode and a calomel
reference electrode filled with saturated sodium or
potassium chloride. Use a salt bridge to isolate the
reference electrode from the test solution.
The following typical settings are for a PAR 174 polaro-
graphic analyzer with mechanical drop timer: drop time,
2 sec; scan rate, 2 mV/sec; display direction, positive;
scan direction, negative; initial potential, -0.900 V;
range, 1.5 V; sensitivity, 0.5 MA for 0.1 mg/1 acrolein,
1 VIA for 0.3 mg/1, and 2 yA for 0.5 mg/1; modulation
amplitude, 100 mV; operation mode, differential pulse;
output offset, negative settings as required. When using
the PAR 174 in combination with the Houston Omnigraphic
2200-3-3 Recorder, adjust recorder Y-axis to 1 V/in.
(0.039 V/mm) and X-axis to 100 mV/in. (3.94 mV/mm) . Other
polarographic instruments probably can be substituted
without loss in sensitivity if they provide differential
pulse of pulse polarographic modes with sufficiently slow
scan rates.17
PROCEDURE
To 10.0 ml of sample, add 1.00 ml of phosphate buffer
solution (pH 7.4) and 100 pi of 10% EDTA solution. Place
the solution in the polarographic cell. Deaerate for 10 min
with oxygen-free nitrogen. Electrically connect solution.
Wait a minute. Make a polarographic scan between -0.9 and
-1.5 V vs. S.C.E. (NaCl). The peak appears at about -1.2 V.
Compare the peak currents with those for standard solutions
similarly prepared. The procedure is applicable to acrolein
concentrations from 0.05 to 0.5 mg/1.
41
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The acrolein consumption (demand) of the sample is deter-
mined by measuring the acrolein remaining after the contact
period and subtracting it from that added initially.
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA 600/7-76-003
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
July 1976 (Approval)
VOLTAMMETRIC DETERMINATION OF ACROLEIN
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
7. AUTHOR(S)
Howe, Lyman H.
TVA E-LB-76-1
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Division of Environmental Planning
Tennessee Valley Authority
Chattanooga, Tennessee 37^01
10. PROGRAM ELEMENT NO.
EHA553
11. CONTRACT/GRANT NO.
IAG D5-E721
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20U60
13. TYPE OF REPORT AND PERIOD COVERED
Milestone
14. SPONSORING AGENCY COOS
15. SUPPLEMENTARY NOTES This study was conducted by the Tennessee Valley Authority as part
of the Federal Interagency Energy/Environment Research and Development Program under
Interagency Agreement D5-E721 with the Environmental Protection Agency.
16. ABSTRACT
A differential pulse polarographic method was developed for acrolein. It is based
oh electrochemical reduction of acrolein at the dropping mercury electrode. With
this method, acrolein can be quantitated in natural and condenser cooling waters at
concentrations of 0.05 to 0.5 mg/1. The sample for acrolein analysis is buffered at
pH 7.2 with 0.09 M phosphate to resist changes in pH, and ethylenediaminetetraacetic
acid is added in a concentration of 0.09% to prevent interference from zinc. The
recovery of acrolein was unaffected by pH in the 6.8-7.6 range and by zinc at
2.0 mg/1. Replicate analyses at concentrations of 0.1 and 0.3 mg/i acrolein in
reagent water gave respective standard deviations of 7.2 and U.l$ and relative
errors of 2.8 and 3-3%. The recommended method is given in the appendix.
Employing differential pulse voltammetry at the glassy carbon electrode, acrolein
was determined with a sensitivity of 10 mg/1. The acrolein was indirectly measured
by forming the sulfite complex and oxidately measuring unreacted sulfite in 0.09 M
phosphate buffer at pH 7.2.
The effectiveness of sulfite in preserving acrolein could not be evaluated as all
attempts failed in quantitatively recovering acrolein at 0.5 mg/1 in the presence
of excess sulfite.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Analytical Methods, Polarographic Analy-
sis, Acrolein, Sulfite, Natural Water,
Condenser Cooling Water, Chemical Analy-
sis, Water Analysis
Acrolein, Sulfite,
Differential Pulse
Polarography, Voltam-
metry, Glassy Carbon
Electrode
18. DISTRIBUTION STATEMENT
Release Unlimited
19. SECURITY CLASS (This Report)
UNCL
21. NO. OF PAGES
52
20. SECURITY CLASS (This page)
UNCL
22. PRICE
EPA Form 2220-1 (9-73)
43
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