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

2June 21, 2010

Cavity ring-down spectroscopy (CRDS)

Absorption enhancement due to cavity: 103 to 105

CRDS independent of laser power fluctuations

No calibration needed

int0

1 1 1Sn

c

Laser

Scan

Detector

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3June 21, 2010

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 laserOI = optical isolatorAOM = acousto-optic modulatorMFC = mass flow controller

4June 21, 2010

Experimental CRDS setup

5June 21, 2010

Motivation to measure acetylene

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

6June 21, 2010

Spectra from breath and ambient air

Air acetylene concentration 0.93 ppbv; Scan time 20 min; Detection limit 120 ppt

7June 21, 2010

System response to C2H2 absorption

8June 21, 2010

Outdoor air – continuous flow

F. M. Schmidt, O. Vaittinen, M. Metsälä, P. Kraus, L. Halonen, Appl. Phys. B (2010)

9June 21, 2010

Day – Night comparison

F. M. Schmidt, O. Vaittinen, M. Metsälä, P. Kraus, L. Halonen, Appl. Phys. B (2010)

10June 21, 2010

Indoor – outdoor air comparison

F. M. Schmidt, O. Vaittinen, M. Metsälä, P. Kraus, L. Halonen, Appl. Phys. B (2010)

11June 21, 2010

Breath collection and sample handling

No adsorption/desorption phenomena in the bags, the gas system tubing and the quartz-coated ring-down cavity

Acetylene can be collected and stored in aluminum breath bags (statistical error for 10 bags: 0.4 ppb)

Acetylene concentration stays within 0.4 ppb for 5 days in the bag

No quantitative difference between alveolar/full breath samples and nose/mouth breathing (non-smokers)

Thus: static measurements were possible

Spectrometer temperature: 22 degrees (room temperature)

Sample pressure in the cavity: 0.1 bar

12June 21, 2010

Study - Background level of C2H2 in breath

40 healthy volunteers

22 male, 18 female, 20 to 63 years old, 31 non-smokers, 9 smokers

Subjects requested to have stayed at sampling location for 30 min prior to breath collection

One full breath sample collected to a breath bag

At the same time: one ambient air sample collected to a second bag

Samples were analyzed on the same day or at least within 48 hours.

13June 21, 2010

Results – Breath acetylene minus air acetylene

Breath C2H2 baseline = Ambient air C2H2 level

Smokers could be identified with a sensitivity and specifity of 100 %

14June 21, 2010

Timer after smoking

15June 21, 2010

Exposure studies

Subject smokes a cigarette or takes a puff

Continuous breathing into CRDS system for up to 30 min

C2H2 decay recorded standing on peak of absorption profile (3 points per second)

For long-term decay: bag samples or shorter intervals of continuous breathing

Fit exponential functions to decay

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

CRDS suitable for fast and direct detection of C2H2 in air and breath

Mean C2H2 mixing ratio in Helsinki outdoor air of ~1 ppbv

C2H2 correlates with CO, human activity and temperature

Strong fluctuations (up to 60 ppbv on a minute time scale) in urban outdoor air during daytime. Single bag measurements unreliable.

Breath C2H2 baseline is equal to ambient air C2H2 level

Smokers were identified with 100 % sensitivity and specifity

Breath acetylene returns to baseline level around 3 hours after exposure. Urban air pollution could impair smoking status assessment

High-time resolution decay measurements could improve knowledge about residence times of gases and related physiological processes

19June 21, 2010

Acknowledgements

Dr Olavi Vaittinen

Dr Markus Metsälä

Peter Kraus

Mirva Skyttä

Prof Lauri Halonen

Academy of Finland