Anal. Chem. 2000, 72, 5847-5851
Flo w An a lys is Me t h o d fo r De t e rm in in g t h e
Co n c e n t ra t io n o f Me t h a n o l a n d Et h a n o l in t h e Ga s
P h a s e Us in g t h e Nit rit e Fo rm a t io n Re a c t io n
Ha Thi-Hoa ng Nguye n, Norim ic hi Ta ke na ka ,* Hiros hi Ba ndow , a nd Ya s ua ki Ma e da
College of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan
tion method10 have detection limits at several ppmv of alcohol
concentration, and therefore, it is difficult to apply these methods
to the determination of the typical concentrations of alcohols in
ambient air at the ppbv level. Another method by Huang et al.,11
which can successfully determine trace level of alcohols, is
preferred to the aqueous sample. Another two methods for the
quantitative analysis of atmospheric alcohol are the method using
a dehydrogenase-based biosensor and the method using gas
chromatography analysis through cryogenic trap processes. The
This paper presents a flow determination method for low
molecular weight alcohols (methanol, ethanol) in the gas
phase using the nitrite formation reaction, which was
developed from an earlier method using a glass bottle. In
this method, the ambient air and nitrogen dioxide (1 0 0 0
ppmv) were allowed to continuously flow in a glass tube,
which had been filled with 1 0 g of P yrex glass beads. The
flow rates of the ambient air and nitrogen dioxide were
3
3
0 and 2 0 cm / min, respectively. The gas-phase alkyl
nitrites produced by the dark reaction of atmospheric
alcohols and nitrogen dioxide on the P yrex glass beads
were then analyzed by gas chromatography with an
electron capture detector. The alcohol concentrations of
the samples were calculated using a calibrated conversion
factor for each alcohol to its nitrite. The detection limits
for the methanol and ethanol are 0 .7 and 0 .5 ppbv,
respectively. This flow method was used to determine the
atmospheric alcohol concentrations and was found to have
the advantages of a short sampling time and simple
quantitative procedure compared with the previously
reported method (glass bottle method). The feasibility of
this method was also established.
12
former has a detection limit of 50-250 ppm. The latter can detect
2,5,13
atmospheric alcohol at the ppbv level,
and the GC-FID method
was used in several studies.14-17 However, polar compounds such
as methanol and ethanol have an affinity for surfaces, leading to
irreversible adsorption on the column. In their results, methanol
and ethanol exhibited badly tailing peaks and it was found to suffer
from integration errors.17
While the concentrations of atmospheric alcohols are at the
ppbv levels, the directly analyzed detection limit for alcohols is
the ppmv level. Therefore, a 1000 time preconcentration is
required. Because alcohols easily dissolve in water, the problem
due to a loss during preconcentration is not easily solved. For
3
example, a cryotrap is plugged by ice when more than 22 mm of
liquid water is frozen. This amount of water corresponds to ∼1.2
The emission sources of alcohols are significant from plants.1
Recently, the use of alcohol-fueled vehicles has increased. More
than 3 000 000 light-duty cars run on ethanol-blended fuel in
Brazil.6,7 Due to the emission from these alcohol-fueled vehicles,
the atmospheric alcohol concentrations are expected to be higher
than that in the past from plant emission sources. Determination
of the concentration of atmospheric alcohol is important. The
detection of low molecular weight ambient alcohol at trace levels
is still a difficult problem. Methods such as the conductometric
-5
3
13
dm of air sampled on a rainy summer day. In most cases, a
water trap was used prior to the alcohol preconcentration in order
to avoid this problem. Goldan et al. reported 15% or less of light
alcohols was lost in the water trap.14
In an earlier study, we used Pyrex glass bottles for ambient
air sampling and the atmospheric alcohols were allowed to react
with nitrogen dioxide on the glass surface of the bottle to convert
(
(
10) Jones, A. W.; Beylich, K. M.; Bjorneboe, A.; Ingum, J.; Morland, J. Clin.
Chem. 1 9 9 2 , 38, 743-747.
11) Huang, G.; Deng, G.; Qiao, H.; Zhou, X. Anal. Chem. 1 9 9 9 , 71, 4245-
8
9
method, electrochemical fuel-cell method, and infrared absorp-
(
1) Kirstine, W.; Galbally, I.; Ye, Y.; Hooper, M. J. Geophys. Res. 1 9 9 8 , 103,
0605-10619.
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(17) Apel, E. C.; Calvert, J. G.; Greenberg, J. P.; Riemer, D.; Zika, R.; Kleindienst,
T. E.; Lonnerman, W. A.; Fung, K.; Fujita, E. J. Geophys. Res. 1 9 9 8 , 103,
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(
(
(
(
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(
(
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1
0.1021/ac000538n CCC: $19.00 © 2000 American Chemical Society
Analytical Chemistry, Vol. 72, No. 23, December 1, 2000 5847
Published on Web 11/02/2000