Schmidt_Ohio2010_talk

Report
Direct detection of C2H2 in
air and human breath by cw-CRDS
Florian Schmidt, Olavi Vaittinen, Markus Metsälä and Lauri Halonen
Laboratory of Physical Chemistry, University of Helsinki, Finland
Cavity ring-down spectroscopy (CRDS)
Laser
Detector
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1
Scan
 int  Sn    
c  0 
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Absorption enhancement due to cavity: 103 to 105
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CRDS independent of laser power fluctuations
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No calibration needed
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Experimental CRDS setup - schematic
Tuning range: 1520-1575 nm
(6350-6575 cm-1)
Cavity Finesse: 390 000
Sensitivity: 7×10-11 cm-1
Acquisition time: 1 s - 20 min
Detected at ppt level:
C2H2, NH3, HCN
Other detectable species:
CH4, N2O, CO, CO2, H2O
ECDL = external cavity diode laser
OI = optical isolator
AOM = acousto-optic modulator
MFC = mass flow controller
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Experimental CRDS setup
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Motivation to measure acetylene
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One of the most common hydrocarbons in the troposphere
Mostly anthropogenic sources (fossil- and biofuels, biomass burning)
Correlates with other combustions gases and VOCs
Trace pollution and exposure to combustion gases (exhausts, smoking)
Baseline of breath C2H2 in the healthy population? Is C2H2 a biomarker
for a medical condition (e.g. Proteus mirabilis bacterial infection)?
Not previously detected in ambient air with high time resolution and
without pre-concentration.
Not previously quantified in breath
GC-MS slow and expensive
Not measurable with PTR-MS and SIFT-MS with standard pre-cursors
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Spectra from breath and ambient air
Air acetylene concentration 0.93 ppbv; Scan time 20 min; Detection limit 120 ppt
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System response to C2H2 absorption
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Outdoor air – continuous flow
F. M. Schmidt, O. Vaittinen, M. Metsälä, P. Kraus, L. Halonen, Appl. Phys. B (2010)
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Day – Night comparison
F. M. Schmidt, O. Vaittinen, M. Metsälä, P. Kraus, L. Halonen, Appl. Phys. B (2010)
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Indoor – outdoor air comparison
F. M. Schmidt, O. Vaittinen, M. Metsälä, P. Kraus, L. Halonen, Appl. Phys. B (2010)
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Breath collection and sample handling
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No adsorption/desorption phenomena in the bags, the gas system
tubing and the quartz-coated ring-down cavity
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Acetylene can be collected and stored in aluminum breath bags
(statistical error for 10 bags: 0.4 ppb)
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Acetylene concentration stays within 0.4 ppb for 5 days in the bag
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No quantitative difference between alveolar/full breath samples and
nose/mouth breathing (non-smokers)
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Thus: static measurements were possible
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Spectrometer temperature: 22 degrees (room temperature)
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Sample pressure in the cavity: 0.1 bar
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Study - Background level of C2H2 in breath
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40 healthy volunteers
22 male, 18 female, 20 to 63 years old, 31 nonsmokers, 9 smokers
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Subjects requested to have stayed at sampling
location for 30 min prior to breath collection
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One full breath sample collected to a breath bag
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At the same time: one ambient air sample
collected to a second bag
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Samples were analyzed on the same day or at
least within 48 hours.
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Results – Breath acetylene minus air acetylene
Breath C2H2 baseline = Ambient air C2H2 level
Smokers could be identified with a sensitivity and specifity of 100 %
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Timer after smoking
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Exposure studies
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Subject smokes a cigarette or takes a puff
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Continuous breathing into CRDS system for up
to 30 min
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C2H2 decay recorded standing on peak of
absorption profile (3 points per second)
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For long-term decay: bag samples or shorter
intervals of continuous breathing
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Fit exponential functions to decay
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Simple 3-compartment model (respiratory tract,
blood, tissue)
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Breath cycles
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Acetylene residence times
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Summary
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CRDS suitable for fast and direct detection of C2H2 in air and breath
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Mean C2H2 mixing ratio in Helsinki outdoor air of ~1 ppbv
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C2H2 correlates with CO, human activity and temperature
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Strong fluctuations (up to 60 ppbv on a minute time scale) in urban
outdoor air during daytime. Single bag measurements unreliable.
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Breath C2H2 baseline is equal to ambient air C2H2 level
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Smokers were identified with 100 % sensitivity and specifity
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Breath acetylene returns to baseline level around 3 hours after
exposure. Urban air pollution could impair smoking status assessment
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High-time resolution decay measurements could improve knowledge
about residence times of gases and related physiological processes
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Acknowledgements
Dr Olavi Vaittinen
Dr Markus Metsälä
Peter Kraus
Mirva Skyttä
Prof Lauri Halonen
Academy of Finland
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