United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S4-87/013 June 1987
c/EPA Project Summary
Analysis of Nitrite in NO2
Diffusion Tubes Using Ion
Chromatography
D. P. Miller
A method was developed for the
analysis of the NO2 collected by a
passive diffusion controlled atmos-
pheric sampling device. The method
measured the total amount of nitrite ion
using ion Chromatography. The preci-
sion obtained under field conditions.
defined as twice the average deviation
of the blanks, was 30 ppb hr. The
overall accuracy of the method in
exposure chamber tests was 20
percent.
The Palmes Tube design was altered
by surrounding the triethanolamine
coated screen with a Teflon liner. The
nitrite was transferred from the diffu-
sion tube sampler to a concentrator
column by flushing the screen with
deionized water in a device Which
minimized contamination due to han-
dling. The total amount of nitrite was
measured using standard ion chro-
matographic techniques.
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
A passive diffusion controlled person-
nel sampler for nitrogen dioxide, known
as the Palmes Tube, is widely used
because it is small and inexpensive, and
therefore easily deployed in large
numbers. The traditional method for
analysis reacts the collected nitrite with
reagents to form a colored solution,
which is then measured quantitatively
with a spectrophotometer. A number of
different laboratories which use the
Palmes Tube have reported the lower
limit of detection is around 300 ppb hr
and the accuracy is around 20 percent
for an exposure time of one week. A
method of analysis which is more sen-
sitive without sacrificing accuracy would
allow shorter exposure times, and would
give significantly more information about
ambient concentrations of nitrogen
dioxide.
The variance of the field blanks deter-
mines the sensitivity of the method. A
major contribution to the blank levels is
exposure of the screens during prepa-
ration and storage of the samplers. A
limitation of the sensitivity of the spec-
trophotometric method is the inability to
concentrate the entire sample within the
light path of the spectrophotometer. Ion
Chromatography is an alternative method
of analysis which may be adapted to
overcome the limitations of sample
concentration.
Procedures
The Palmes Tube design was altered
by placing the triethanolamine screen
within a Teflon liner, which then fit into
the closed end of the diffusion tube. The
acrylic diffusion tube was replaced by a
stainless steel tube. A transfer apparatus
was constructed which accommodated
the sampler. Deionized water was used
to rinse the collected nitrite from the
screen. The entire nitrite sample on the
screen was transferred and trapped on
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a concentrator column in an ion chro-
matograph. The nitrite was then resolved
chromatographically and quantified
using a conductivity detector.
To reduce contamination to an accep-
table level, all sampler parts were soaked
in sodium hydroxide solution prior to
preparation of the sampler. The freshly
coated screens were dried in a stream
of purified nitrogen gas. No convenient
method was found which allowed
exposed tubes to be stored for a rea-
sonable length of time before analysis.
Results and Discussion
The limit of detection was 6 ppb hr,
which was at the noise level of the
instrument. The achievable accuracy
under field conditions which included
shipping the samplers before and after
exposure for a total of four days between
preparation and analysis, was 20 percent
at the 70 ppb hr exposure level. Field
blanks and field blank deviations
increased with the time between prep-
aration and analysis. One day lapse time
gave an average blank deviation of 6 ppb
hr, but at four days, the average blank
deviation increased to 30 ppb hr. The
overall precision and accuracy of the
method was limited by the perishable
nature of the sampling device. In order
to obtain precision which approaches the
sensitivity of the method, ways to store
the samplers both before and after
exposure will be required.
Interferences collected by the sampler
under ambient sampling conditions, both
carried as a personnel monitor and at
stationary locations, were small and did
not affect the precision. Contamination,
usually caused by poor handling, was
easily recognized by an unusually large
chloride peak. The throughput using the
ion chromatographic method of analysis
was roughly half the throughput using
the traditional spectrophotometric
method.
D. P. Miller is with Washburn University, Topeka, KS 66621.
James D. Mulik is the EPA Project Officer (see below).
The complete report, entitled "Analysis of Nitrite in NO2 Diffusion Tubes Using
Ion Chromatography," (Order No. PB 87-188 777/AS; Cost: $11.95) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer 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 $300
EPA/600/S4-87/013
0000329 P$
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