United States
Environmental Protection
Agency
Atmospheric Sciences Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-85/021 May 1985
\°/EPA Project Summary
Analysis of Aldehydes and
Ketones in the Gas Phase
L A. Hull
Carbonyl compounds, especially al-
dehydes and ketones, play a key role in
the photochemical smog-forming proc-
ess. Because of this, their analysis has
received considerable attention. In this
Project Summary, some of the details
of the testing and use of the 2,4-dinitro-
phenylhydrazine-acetonitrile (DNPH-
ACN) method for the determination of
aldehydes in ambient air are discussed.
A discussion of interferences, the prep-
aration of calibration standards. High
Performance Liquid Chromatograph
(HPLC) column evaluation, analytical
testing, dicarbonyl-DNPH analysis, fluo-
rescence methods, preliminary car-
tridge testing, and the results of atmos-
pheric sampling in Schenectady, NY,
and atmospheric and cloudwater sam-
pling on Whiteface Mountain in Wil-
mington, NY, are included.
This Project Summary was developed
by EPA's Atmospheric Sciences Re-
search Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Carbonyl compounds are an important
constituent of photochemical smog. They
are emitted from the tailpipes of auto-
mobiles; they are produced during the
photooxidation of hydrocarbons, and they
are active participants in free radical-
chain reactions. Computer models simu-
lating the chemical reactions in urban
atmospheres require a knowledge of
formaldehyde and other aldehyde con-
centrations.
Because of the key role of aldehydes
and ketones in atmospheric chemistry.
their analysis has received considerable
attention. Recent advances in high per-
formance liquid chromatography (HPLC)
techniques have prompted the develop-
ment of a number of methods that depend
on derivatization of the aldehydes and
HPLC separation of the derivatives. One
of these techniques involves the reversed-
phase separation of 2,4-dinitrophenylhy-
drazine (DNPH) aldehyde derivatives.
Another technique involves an extraction
method based on DNPH derivatization
followed by HPLC analysis and uv detec-
tion. Another more recent development
involves the use of 2-diphenylacetyl-1,3-
indandione-1-hydrazone (DAIH) to form
fluorescent azine derivatives of the al-
dehydes; this is followed by HPLC separ-
ation of the derivatives and detection of
the derivatives by fluorescence emission
at 525 nm. Another adaptation of the
DNPH-acetonitrile (ACM) method has
recently been reported. In that work, a
DNPH-ACN solution was used to coat a
da-based cartridge that was then used
for atmospheric sampling. The cartridge
is leached out with acetonitrile after the
air sampling and the leachate is analyzed.
In this Project Summary, some of the
details of the testing and use of the
DNPH-ACN methods are discussed. In-
cluded are a discussion of interferences,
the preparation of calibration standards,
HPLC column evaluation, analytical test-
ing, dicarbonyl-DNPH analysis, fluores-
cence methods, preliminary cartridge
testing, and the results of atmospheric
sampling in Schenectady, NY, and at-
mospheric and cloudwater sampling on
Whiteface Mountain in Wilmington, NY.
Also, one of the potential applications of
the various aldehyde-ketone analysis
techniques is to the analysis of C2-C4
dicarbonyl compounds such as glyoxal,
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methylglyoxal, and biacetyl. Previous
work had shown that DNPH derivatives
could be formed and detected under the
conditions of the analysis. There was,
however, ambiguity about whether the
material being detected in the analysis
was the mono- or the di-DNPH derivative
of the dicarbonyls and whether there was
some analytical interaction among the
dicarbonyl compounds. An effort was
made in this study to resolve these
ambiguities.
Procedure
Authentic samples of the DNPH deriv-
atives, of a representative collection of
aldehydes and ketones were synthesized.
The samples served as calibration stand-
ards and aided in the development of
optimal HPLC conditions for analysis.
In order to resolve the ambiguities in
the chromatographic behavior of the
mono- and di-DNPH derivatives of the C2-
C4 dicarbonyl compounds, two approach-
es were used. In the first approach,
solutions were made with large and small
dicarbonyl-to-DNPH ratios. In the second
approach, attempts were made to isolate
authentic solid samples of the mono and
di-DNPH derivatives.
The use of DAIH and 1 -dimethylamino-
naphthalene-5-sulfonylhydrazine(dansyl
hydrazine) as analytical reagents for
aldehyde determination was also tested.
The preparation of the appropriate car-
bonyl compound derivatives was per-
formed and their chromatographic behav-
ior determined. A comparison of that
behavior with that of the DNPH deriv-
atives was made. Some preliminary ex-
periments were also performed to com-
pare the impinger DNPH method to a
previously-developed cartridge method.
The method allows for sampling with a
cartridge coated with silica-C18 impreg-
nated with a DNPH-ACN phosphoric acid
mixture. The technigue not only promises
a simplified procedure, but it also has the
potential of increasing sensitivity.
To provide information on ambient
aldehyde levels and to test out the DNPH
method under field conditions, three
projects were undertaken. In the first, air
in Schenectady, NY, was monitored daily
during July and August of 1983. The
second project consisted of sampling air
at the State University of New York at
Albany's (SUNYA) Atmospheric Sciences
Research Center (ASRC) on Whiteface
Mountain in Wilmington, NY, for one
week during August 1983. In the third
project, a variation of the DNPH method
was used during July-August 1984 for
2
aldehyde and ketone determinations in
cloudwater atop Whiteface Mountain.
Results
The synthetic samples of the DNPH
derivatives of the simple aldehydes and
ketones were determined by HPLC to be
in excess of 99% pure. The chief impurity
in each case was a small amount of the
unreacted DNPH reagent itself. The uv
detector response to each of the solutions
at two wavelengths (254 nm and 360 nm)
was evaluated. For all the derivatives the
calibration curves were linear.
Two columns were evaluated in this
study: a Varian MCH-10(C-18), 25 cm x
4.6 mm, 10 microns and an Alltech C-18
column, 25 cm x 4.6 mm, 10 micron. The
Alltech column was found to give the best
separation and allowed for the resolution
of several pairs of components that were
of identical molecular weight but different
structures. In particular, acrolein, ace-
tone, and propanal could be resolved with
this column.
Cross comparison of the DNPH method
and chromotropic acid (CA) assay method
for formaldehyde was performed in the
concentration range 60 to 1400 ppb. The
formaldehyde source was a permeation
tube that consisted of solid paraformal-
dehyde encased in a Teflon tube held at a
constant temperature. Within about ten
percent, the results of the DNPH method
and the CA method were found to be in
agreement.
Four DNPH reagent solutions were
prepared and stored in different types of
containers. Periodically, samples from
each of the solutions were withdrawn
and analyzed by HPLC. After two weeks
there was no detectable contamination in
Teflon- or glass-stoppered containers. In
the plastic-capped vial, however, there
was a noticeable buildup of a peak having
the same retention time as the benzal-
dehyde DNPH derivative. After two weeks,
a steady buildup of impurities was ob-
served in the reagent regardless of the
container if acid had been added. In
unacidified reagent there was no in-
crease in contamination until acid was
added. In addition, the stability of solu-
tions after atmospheric sampling was
determined. Samples of the Schenectady,
NY, air were taken by passing 90 liters of
air through the DNPH-acetonitrile solu-
tions in the standard fashion. The result-
ing solutions, stored in Teflon-capped
vials in a refrigerator were periodically
analyzed. The results for the analysis of
the stored DNPH-ACN solutions snowed
that the solutions appeared to be stable
for as long as three weeks after collection.
Limits of detection (LOD) and limits of
guantification (LOQ) for the DNPH-aceto-
nitrile technigue were also determined.
The LOD was defined as a signal that was
greater than three standard deviations
from the average background signal. The
LOQ was defined as a signal greater than
ten standard deviations from the average
background signal. The LOD and LOQ for
formaldehyde were 0.10 ppb and 0.32
ppb, respectively, and for acetaldehyde
were 0.16 ppb and 0.53 ppb, respectively,
for a 90 liter air sample. With the excep-
tion of acetone, the other aldehydes and
ketones gave about the same instability in
baseline as the acetaldehyde and their
detection limits were about the same
(0.16 ppb LOD and 0.53 ppb LOQ for a 901
sample). Acetone was found in the rea-
gent at exceedingly high and unstable
concentrations. The contamination of the
reagent, apparently due to the impurity in
the acetonitrile, led to the inability to
monitor acetone levels.
Efforts were also made to determine
the chromatographic behavior of the
mono- and di-DNPH derivatives of the C2-
C4 dicarbonyl compounds. Two approach-
es were used. In the first approach
solutions were made with large and small
dicarbonyl-to-DNPH ratios. In the second
approach attempts were made to isolate
authentic solid samples of the mono and
di-DNPH derivatives. The experiments at
high dicarbonyl-to-DNPH ratios showed
short retention times for polar C2-C4
mono-DNPH materials. Two peaks were
observed in the high ratio run for methyl-
glyoxal, one at 4.2 min and the other at
4.5 min comprising 20% and 80% of the
mixture, respectively. The two peaks
presumably represent the two isomers of
methylglyoxal. In contrast, the exper-
iments at low ratios, where di-deriva-
tization is likely, show longer retention
time materials (7.9-15.1 min). These
longer retention time materials are, pre-
sumably, the di-DNPH derivatives. The
preparation of the mono-DNPH deriva-
tives was successful only for biacetyl. The
solids isolated for glyoxal and methyl-
glyoxal showed significant contamination
with the di-DNPH derivative. Preparation
of the di-DNPH derivatives went smoothly
and HPLC analysis showed that the
materials were reasonably pure (>95%).
The solid derivatives were used to make
up a solution to calibrate the HPLC
responses. Also, estimates of the HPLC
responses for the mono-DNPH derivatives
of glyoxal and methylglyoxal were calc- (
ulated from the dicarbonyl-to-DNPH ratio
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experiments described before. There
were some correlations in the response
factors of the various DNPH derivatives by
functional group class. The most sensitive
measure of the functional group class
appeared to be the 360 nm/254 nm uv
response ratio. The large ratio (1.0) given
by the dicarbonyl di-DNPH derivatives
was easily distinguished from the cor-
responding ratiofor simple monocarbonyl
DNPH derivatives (0.49).
The method for determination of alde-
hydes based on the reaction DAIH fol-
lowed by HPLC separation and fluores-
cence detection was examined. After
comparing detection limits for this
method with that of uv absorption and the
DNPH method, the DAIH method was
found to be inferior. Both the uv method
and the DNPH method were about 25
times more sensitive. Preliminary results
obtained with the dansyl hydrazine meth-
od also suggest that this method is inferior
to the DNPH method. The more complex
HPLC separations and the lack of re-
activity with aromatic aldehydes suggest
that this reagent may require sophisti-
cated HPLC techniques and careful inter-
pretation of the results.
A comparison of the cartridge method
with that of the impinger DNPH-ACN
method was also performed for formal-
dehyde. The results were very encourag-
ing. Not only were the values for each
dilution run comparable, but it appeared
that the cartridge technique was more
efficient. The chromatograms for the
second cartridge in the series of two were
cleaner than the chromatograms for the
second of the two impinger in the solvent-
based method. The average absolution
error was about 7% and there appeared to
be no systematic bias.
The July-August 1983 sampling data
from Schenectady, NY, principally showed
formaldehyde and acetaldehyde. All the
data for formaldehyde were in the quanti-
fication range and went from a low of
0.70 ppb to a high of 30.5 ppb with an
average daily concentration of 7.6 ppb.
Although there was a large variation in
the daily data, there was a general trend
toward lower formaldehyde concentra-
tions over the course of the summer. The
concentration of acetaldehyde was al-
ways significantly below that of formal-
dehyde. When the amount of acetalde-
hyde was detectable, the ratio of formal-
dehyde to acetaldehyde averaged about
14:1. Since acetaldehyde was below its
detection limit of 0.16 ppb in the vast
majority of samples, the average ratio for
those samples was greater than 48:1.
The variation on formaldehyde over the
course of the day was explored by sam-
pling every three hours for 36 hours.
There were two peaks in the formalde-
hyde concentration over the course of the
day. The first occurred about 7:00 -10:00
a.m. and the second about 6:00 - 10:00
p.m. The peaks seemed to be clearly
correlated with commuting automobile
traffic. The daily minimum occurred at
about 3:00 a.m. Over a 24-hour period,
the ra nge of formaldehyde concentrations
was 1.7-8.1 ppb.
The work at the SUNYA ASRC station
was done over a period of one week
(August 14-20, 1983). No significant
quantities of any aldehydes other than
formaldehyde and acetaldehyde were
detected. Formaldehyde concentrations
ranged from 0.6-2.6 ppb. Acetaldehyde
levels ranged from below the LOD of 0.16
ppb to a barely measurable 0.80 ppb. It
was apparent that there was a tendency
for the aldehydes to rise and fall with the
ozone. Formaldehyde concentrations
were found to reach a peak between
10:00 - 12:00 in the evening. The daily
minimum occurred about 12:00 - 2:00 in
the afternoon. Presumably the pattern
reflects the fact that the chief mechanism
for loss of formaldehyde is photolysis.
Not unexpectedly, the formaldehyde
levels observed at Whiteface were signif-
icantly less than the levels in Schenec-
tady. During the same weekthe work was
performed at Whiteface, the levels of
formaldehyde in Schenectady averaged
6.7 ppb and ranged from 3.2-9.5 ppb.
Schenectady is about 90 miles south of
Wilmington, NY, and during that week
was influenced by the same weather
systems. The average level of formalde-
hyde at Whiteface was about 1.3 ppb and
ranged from 0.6-2.6 ppb. The formalde-
hyde levels differed by roughly a factor of
five. The acetaldehyde data is difficult to
interpret with any certainty. The data
from each location are limited. There is,
however, some indication that acetalde-
hyde, when detectable, is at about the
same level on Whiteface Mountain as in
.Schenectady, NY.
In the cloudwater work during the July-
August 1984 period, samples were taken
directly from the cloud water collectors
atop Whiteface Mountain every one to
two hours during a cloud cover event. The
samples were added to the DNPH reagent
solution within ten minutes. The resultant
solutions were then refrigerated for sub-
sequent analysis. The maximum delay
time between reagent mixing and anal-
ysis was five days; the majority of anal-
yses were done within two day*. Aque-
ous-based reagents showed significant
changes in formaldehyde and acetalde-
hyde concentrations with time while the
acetonitrile-based reagent showed chang-
es of no more than about 15%. The
stability of the actual cloudwater samples
was also determined to be more than a
week. All samples taken using the ACN
solution yielded quantifiable results
above blank levels. There were consist-
ently only three carbonyl compounds
present. Formaldehyde ranged in concen-
tration from 0.33-14.8 micromolar. Acet-
aldehyde and acetone were usually de-
tected at levels that were comparable to
these of formaldehyde.
Conclusion
The DNPH method of trapping and
quantifying aldehydes in ambient air
appears to be efficient and accurate. The
method is not sensitive to interferences
by common atmospheric contaminants.
An Alltech C-18 HPLC column is recom-
mended for rapid, efficient analytical
separations of the C1-C4 aldehydes. The
uv detection of the derivatives should be
done at 360 nm but the 360/254 area
ratio may aid in the determination of the
nature of unknown materials and serve to
confirm identifications made on the basis
of retention times.
The DNPH reagent is stable when kept
in glass- or teflon-capped containers for
up to four weeks. If no acid is added to the
reagent, it appears to be stable for several
months. It is recommended that acidified
reagent be used within two weeks. The
sampled reagent appears to be stable for
at least three weeks after sampling if it is
refrigerated. It is recommended that
analyses be performed within two weeks
of sampling and that the samples be
stored in teflon-sealed vials under refrig-
eration. The LOD and LOQ for the DNPH
method are such that formaldehyde is
readily determinable even in "clean" air,
but information on the other carbonyl
compounds may be limited to urban areas.
Analysis of dicarbonyl compounds with
the DNPH method requires special care
because of the extreme insolubility of the
di-DNPH derivatives. In particular, sam-
pling times have to be carefully adjusted
based on anticipated concentrations so
as not to exceed the solubility limits for
the derivatives. In addition, the HPLC
analysis should be done at higher ACN
levels than the standard analysis to avoid
column precipitation and to shorten the
retention times.
Although t*f» WPH-ACN method is
useful for trtrgrtef miration of aldehyde
levels v^««VMtitf lafloratory faci lities
available, « to toKJowenient for field
3 ~" . ': •
-------
sampling. The necessity of handling a
volatile, flammable, regulated organic
solvent limits the kinds of situations
suitable for DNPH-acetonitrile sampling.
Preliminary testing of a DNPH cartridge
technique has shown it to be accurate
and more convenient than solvent-based
alternatives. It is recommended that
future work be devoted to the use of
DNPH cartridge sampling for aldehyde
determinations. Methods based on other
hydrazine chromophores (DIAH and
dansyl hydrazine) appear to offer no
substantial advantages over DNPH while
suffering from more difficult and longer
analyses and inefficiencies in derivati-
zation.
DNPH-ACN reagent solutions with sub-
sequent HPLC analysis may prove useful
for sampling rain and cloudwater for
aldehydes. The preliminary work reported
here indicates that the levels of acetalde-
hyde and acetone are comparable to that
of formaldehyde.
L A. Hull is with Department of Chemistry, Union College, Schenectady, NY
12308.
Marcia Dodge is the EPA Project Officer (see below).
The complete report, entitled "Analysis of Aldehydes and Ketones in the Gas
Phase," (Order No. PB 85-181 865/AS; Cost: $ 10.00, 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
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