United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S4-88/022 Aug. 1988
&ERA Project Summary
Investigation of
2,4-Dinitrophenylhydrazine
Impregnated Adsorbent
Tubes for the Collection of
Airborne Aldehydes
M. Holdren, D. Smith, and N. Russell
The objective of this study was to
investigate the use of 2.4-dinitro-
phenylhydrazine (DNPH) impregnated
adsorbents for sampling airborne alde-
hydes. Investigation focused primarily
on the Sep-Pak Cm adsorbent material
because it has been used in the past
by researchers to sample airborne
aldehydes and it is available as a
commercially prepared cartridge.
Experimental results using a 17 m3
environmental chamber and various
spiked amounts of aldehyde material
(low ppb levels) showed that the
DNPH-coated cartridge and the
DNPH/acetonitrile impinger methods
gave equivalent results. Blank levels of
the DNPH-coated cartridges were
studied as a function of storage time
using various containers and temper-
ature conditions. Canisters pressurized
with zero-grade nitrogen provided the
best storage device. Lower blank levels
were also obtained when the cartridges
were stored at lower temperatures.
Blank levels appear to equilibrate after
six days of storage. Significant batch-
to-batch differences in blank levels
were observed. To assure that quality
data will be obtained, cartridges should
be grouped according to batch number
and blank levels should be determined
prior to any field monitoring effort.
Blank cartridge levels should be an
order of magnitude lower than the
sample cartridge level. Adjustment in
sampled volume should be made
accordingly. High performance liquid
chromatography with UV detection
proved to be a sensitive and stable
analytical method for the DNPH deriv-
atives. Three laboratories employing
the above sampling and analysis
methodology reported similar results
after analyzing an eight component
aldehyde derivative standard (2 ng/jul).
Results of field sampling demonstrated
that low ppb levels of airborne alde-
hydes can be determined with good
analytical precision.
This report is being submitted in
fulfillment of Contract No. 68-02-
4127 by Battelle Columbus Division
under the sponsorship of the U.S.
Environmental Protection Agency. It
covers a period from February 1, 1987
to September 30,1987, and work was
completed as of September 30, 1987.
This Project Summary was devel-
oped by EPA's Environmental Monitor-
ing Systems 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 information at back).
Introduction
The determination of aldehydes and
other carbonyl compounds in the atmos-
phere is of interest because of their
importance as precursors in the produc-
tion of photochemical smog, as photo-
chemical reaction products and as a
-------
major source of free radicals in polluted
environments. Additionally, short-term
exposures to aldehydes such as formal-
dehyde, acetaldehyde, acrolein and
crotonaldehyde are known to result in
irritation of the eyes, skin and mucous
membrane of the upper respiratory tract.
These carbonyl species are emitted
into the atmosphere either directly from
certain industrial processes or as secon-
dary products from combustion sources.
In rural areas, concentrations of 0.6 to
1.3 ppb formaldehyde have been
reported. In urban environments, formal-
dehyde levels range from several ppb to
over 50 ppb depending upon location and
meteorological conditions. Acetaldehyde
levels 20 to 50 percent of formaldehyde
concentrations are generally found. Very
little ambient air data exist, however, for
the other carbonyl species.
The limited amount of speciated alde-
hyde data is largely due to the lack of
a simple, sensitive, and selective analyt-
ical method. Derivatization techniques
utilizing 2,4-dinitrophenylhydrazine
(DNPH) reagent are currently being
evaluated and will likely replace the
earlier analytical methods—chroma-
tropic acid, pararosaniline, and direct
analysis via gas chromatography. With
the DNPH technique, a derivative is
formed by the reaction of DNPH with the
carbonyl compound in the presence of
acid to form the correspondi ng hydrazone
derivative. Initially, the DNPH derivatives
were separated and identified using
packed column gas chromatographic
techniques. More recently, high perform-
ance liquid chromatography (HPLC) has
been employed by researchers to more
easily separate and elute the DNPH
derivatives. Quantitation of the hydra-
zone derivatives using HPLC is accomp-
lished with a UV detector.
Sampling for carbonyl species is
generally accomplished with either
impinger or solid adsorbent techniques.
With impinger methods, aqueous or
organic solvents (or mixtures of both)
have been used to prepare the DNPH
absorbing solution. The use of DNPH/
acetonitrile solutions permit the direct
analysis of the adsorbing solution using
reversed phase HPLC. The DNPH/ace-
tonitrile impinger technique has simpli-
fied sampling efforts, but it is not ideally
suited for extended sampling periods
(solvent evaporation) nor for field use
when samples are to be stored and
shipped to a central laboratory for
analysis. The use of adsorbent traps
coated with DNPH circumvents some of
the short-comings of the impinger tech-
nique. Adsorbents that have been
impregnated with DNPH include XAD-2,
silica gel, glass beads, commercially
packaged plastic cartridges (e.g., Sep-Pak
C18), and glass fiber filters.
The objective of this study was to
further investigate the use of DNPH
impregnated adsorbent for sampling
airborne aldehydes. Specific areas that
were examined include:
• determination of collection and re-
covery efficiency of adsorbent tubes
versus impingers
• design of leak-tight sample storage
devices/improvement of adsorbent
tube design
• improvement of sampling/analysis
accuracy and precision for ambient
aldehydes
• investigation of alternative detection
schemes.
Procedures
A Varian model 5000 liquid chromat-
ograph served as the primary analytical
tool. A Hewlett Packard model 5890 gas
chromatograph coupled to a flame ion-
ization and an electron capture detector
was also employed to determine if better
selectivity and sensitivity for the hydra-
zone derivatives could be achieved. A
third method, a continuous monitoring
analyzer (CEA, Inc.), was tested for its
selectivity and sensitivity for
formaldehyde.
DNPH material showed unacceptable
impurity levels and was purified by a
crystallization process. The purified
crystals were then accurately weighed-
out and dissolved in acidified acetonitrile
solution to form the stock adsorbing
solution. Carbonyl-DNPH derivatives
were prepared by adding the individual
carbonyl compound to an acidified
saturated solution of DNPH. The colored
precipitate was filtered and washed with
HCI/H20 mixture and dried. The deriv-
ative was recrystallized in methanol if the
purity level was unsatisfactory. A stand-
ard stock solution of each aldehyde
derivative (20 mg/L) was prepared and
checked throughout the study for pos-
sible degradation. Working calibration
standards (2 mg/L) were prepared from
the stock mixtures. These working
standards were used on a daily basis.
Sep-Pak cartridges were used as the
primary sampling devices. The coating
procedure for these adsorbent sampling
tubes involved adding 10 ml absorbing
solution (gravity feed), draining the
excess solution and then drying the
cartridges with clean N2gas. After drying,
the tubes were sealed with aluminum
end caps and placed in a storage vessel.
Three types of storage containers were
tested to determine the effect of blank
levels versus time. These containers
include: a stainless steel canister pres-
surized with N2, an aluminum can
containing a bed of charcoal and a glass
vial with a Teflon-lined screw-cap.
Temperature effects during storage were
also examined. Coated cartridges were
stored at room temperature, in the
refrigerator and in the freezer.
Blank levels from several batches of
the Sep-Pak cartridges were examined.
Likewise silica gel, Tenax, and Maxiclean
cartridges (Alltech) were also coated and
tested to determine if lower blank levels
could be achieved.
Impinger samples were collected at a
nominal flow rate of 1 L/min using a
single impinger containing 10 ml of the
DNPH solution. Cartridge samples were
collected at nominal flow rates ranging
from 0.06 to 0.80 L/min. The cartridges
were sampled either individually or in
tandem.
A Teflon-lined aluminum 17 m3 envir-
onmental chamber was used to facilitate
the evaluation of the CEA formaldehyde
analyzer and to carry out the impinger/
cartridge comparison studies.
Results
Experimental results using a 17 m3
environmental chamber and various
spiked amounts of aldehyde material (39
to 236 ppb) showed that the DNPH coated
Sep-Pak cartridge and the DNPH/ace-
tonitrile impinger methods gave equival-
ent results. Cartridge/impinger ratios >
0.85 were obtained for most of the tested
aldehydes (acrolein ratio = 0.74). Based
on the calculated chamber concentra-
tions, both sampling methods showed
absolute recoveries greater than 80
percent for formaldehyde, acetaldehyde,
butyraldehyde and benzaldehyde. Acro-
lein recoveries ranged from 281 to 44
percent. For crotonaldehyde, recoveries
of 127 to 159 percent were found.
Blank levels of the DNPH-coated Sep-
Pak cartridges were generally 1 nano-
gram or less (formaldehyde derivative).
However, one batch of Sep-Pak car-
-------
tridges exibited 8-fold higher blank
levels. Alternative adsorbents, such as
silica gel, Tenax, and Maxiclean-coated
cartridges, showed blank levels similar
to the latter batch of Sep-Pak material.
Canisters pressurized with nitrogen
provided the best storage container for
the coated Sep-Pak cartridges. Storage
in a refrigerator or freezer also resulted
in lower blank levels than storage at room
temperature. Test results showed that
cartridge blank levels did not appear to
increase significantly after the sixth day
of storage.
Results from samples (in triplicate)
collected at a suburban location showed
good analytical precision and low blank
levels. Aldehyde concentrations ranged
from 0.34 to 7.04 ppb and four of the
five measured compounds showed
standard deviation values less than 10
percent. Acetone's S.D. values averaged
—23 percent. For the sample blanks,
formaldehyde averaged 0.15 ppb, ace-
tone averaged 0.10 ppb and the remain-
ing aldehydes were not detected.
High performance liquid chromatog-
raphy was shown to be a sensitive and
stable analytical method for the hydra-
zone derivatives. The system was able
to detect 0.2 nanograms of formaldehyde
derivative (injected on-column with a 10
/j\ sample size). Very good precision (<4
percent RSD) was obtained from the
analyses of an eight component standard
(2 ng/yul) over a two month period.
Results from the analyses of the eight
component standard by three laborato-
ries agreed very well. Although gas
chromatographic methods using an
electron capture detector gave better
sensitivity, a considerable number of
extraneous peaks prohibited acceptable
identification and quantitation of the
aldehyde derivatives.
The continuous monitoring analyzer
was able to detect > 8 ppb formaldehyde
and was nonresponsive to ppb levels of.
other aldehydes. The unit was also
compared with the impinger and car-
tridge sampling methods. At a chamber
loading of 57 ppb, an average formalde-
hyde reading of 63 ± 6 ppb was obtained
with all three methods. An average value
of 197 ± 19 ppb was found at a chamber
loading of 221 ppb.
Conclusions and
Recommendations
Based on the results of this work, it
is concluded that the DNPH-coated Sep-
Pak cartridges provide the researcher
with a simple yet accurate means for
sampling airborne aldehydes. Further-
more the analysis of the hydrazone
derivatives isfacilitated by the use of high
performance liquid chromatographic
methodology. Specific conclusions and
recommendations are given below:
1. Experimental results using a 17 m3
environmental chamber and various
spiked amounts of aldehyde material
showed that the DNPH-coated Sep-
Pak cartridge and the DNPH/aceton-
itrile impinger methods gave equiv-
alent results. Cartridge/impinger
ratios of > 0.85 were obtained for
most of the tested aldehydes (acro-
lein ratio = 0.74). Based on the
calculated chamber concentrations,
both sampling methods showed
absolute recoveries greater than 80
percent for formaldehyde, acetalde-
hyde, butyraldehyde and benzalde-
hyde. Considering the generated
concentration levels and the adsorp-
tive nature of these compounds, the
above absolute recovery is quite
acceptable. However for acrolein,
recoveries ranged from 28 to 44
percent. For crotonaldehyde, recov-
eries of 127 to 159 percent were
found. Both compounds are olefinic
aldehydes and it is likely that these
species undergo additional chemical
reactions during the sampling and
analysis process. We do not recom-
mend using the cartridge sampling
approach for these two carbonyl
species.
2. Blank levels of the DNPH coated Sep-
Pak cartridges were investigated as
a function of storage time using
various containers and temperature
conditions. Canisters pressurized
with nitrogen provided the best
storage device. Storage in a refrig-
erator or freezer also resulted in
lower blank levels than storage at
room temperature. Coated car-
tridges showed no detectable
amount of the aldehyde derivatives
when analyzed within several hours
of preparation. However, we found
measurable levels after six days of
storage. Blank levels did not appear
to increase significantly after the
sixth day. During these tests, several
different batches of the Sep-Pak
cartridges were housed within the
same storage device. We observed
an eight-fold difference in blank
levels. This batch-to-batch differ-
ence may significantly affect the
quality of data collected during a
monitoring study. To assure that
quality data will be obtained, car-
tridges should be grouped according
to batch number and blank levels
should be determined prior to any
field monitoring effort. We recom-
mend that the blank cartridge level
be an order of magnitude lower than
the sample cartridge level (i.e.,
adjust sampled volume accordingly).
3. High performance liquid chromatog-
raphy was shown to be a sensitive
and stable analytical method for the
hydrazone derivatives. Very good
precision was obtained from the
analyses of an eight component
standard (2 ng/yul) over a two month
period. Although gas chromato-
graphy methods were also examined
and gave better sensitivity, a consid-
erable number of extraneous peaks
prohibited acceptable identification
and quantitation of the aldehyde
derivatives.
4. Good interlaboratory agreementwas
obtained from the analysis of an
eight component standard (2 ng/fA).
These results demonstrate that the
hydrazone derivatives can be pre-
pared accurately at the lower ng//ul
level and are stable in solution for
at least four months.
5. Aldehyde samples collected at a
suburban location showed good
analytical precision and low blank
levels. These results demonstrate
that low ppb levels of airborne
aldehydes can be determined with
the sampling and analysis methodol-
ogy discussed in this report.
6. A continuous monitoring analyzer
was evaluated and exhibited good
sensitivity and selectivity for formal-
dehyde. The unit was able to detect
> 8 ppb formaldehyde and was
nonresponsive to ppb levels of other
aldehydes.
-------
M. W. Holdren. D. L Smith and N. K. Russel are with Battelle's Columbus
Division. Columbus. OH 43201-2693.
W. A. McClenny andJ. D. Mulik are the EPA Project Officers (see below).
The complete report, entitled "Investigation of 2,4-Dinitrophenylhydrazine
Impregnated Adsorbent Tubes for the Collection of Airborne Aldehydes,"
(Order No. PB 88-220 223/AS; Cost: $14.95, 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 Officers can be contacted at:
Environmental Monitoring Systems 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 $300
EPA/600/S4-88/022
OC00329 PS
------- |