QCLAS and CRDS-Based CO Quantification as Aimed at in Breath Measurements

Abstract

Laser-spectrometric methods to derive absolute and traceable carbon monoxide (CO) amount fractions in exhaled human breath could be of advantage for early disease detection as well as for treatment monitoring. As proof-of-principle laboratory experiment, we employed intra-pulse and continuous wave (cw) quantum cascade laser spectroscopy (QCLAS), both at 4.6 μm. Additional experiments were carried out applying cw cavity ring-down spectroscopy (CRDS) with a CO sideband laser and a QCL. We emphasize metrological data quality objectives, thatis, traceability and uncertainty, which could serve as essential benefits to exhaled breath measurements. The results were evaluated and compared on a 100 μmol/mol CO level using the two QCLAS spectrometers, and the cw CO sideband laser CRDS setup. The relative standard uncertainties of the pulsed and the cw QCLAS CO amount fraction results were ±4.8 and ±2.8%, respectively, that from the CO sideband laser CRDS was ±2.7%. Sensitivities down to a 3 nmol/mol CO level were finally demonstrated and quantified by means of cw CRDS equipped with a QCL yielding standard uncertainties of about ±2.5 that are exclusively limited by the available line strength figure quality. With this study we demonstrate the achieved comparability of CO quantifications, adhering metrological principles.

Carbon monoxide in exhaled breath testing and therapeutics

“…At the experimental stage, several novel techniques based on infrared laser spectroscopic methods have been recently developed which report enhanced sensitivity for CO in the parts per billion (ppb) range. Variations on these techniques include cavity leak out spectroscopy (CALOS), integrated cavity output spectroscopy (ICOS), cavity ring-down spectroscopy (CRDS) and quantum cascade laser absorption spectroscopy (QCLAS) [78][79][80][81][82][83][84].…”

Traceable amount of substance fraction measurements in gases through infrared spectroscopy at PTB

“…Absolute TDLAS measurements based on TILSAM have been shown to yield relative expanded uncertainties in the low percent range [5,17] and TILSAM instrumentation may be used to certify gas mixtures or as optical transfer standard [10]. TILSAM can also be applied for absolute measurements based on CRDS [30,31], extending its scope to the measurement of trace concentrations. PAS is another technique well suited for trace gas detection but needs calibration with reference gases and is thus not yet addressed by the TILSAM method.…”

Applications of Absorption Spectroscopy Using Quantum Cascade Lasers

“…A time resolution of less than 1 s and a detection limit of 7 ppb Hz −1/2 were obtained, 146 and different spectroscopic techniques for CO quantifications were compared. 147 In 2011, Rubin et al 148 used a pulsed DFB-QCL in the spectral region around 2300 cm −1 in a flow-through system for 12 CO 2 / 13 CO 2 isotope ratio determination in human breath. The analysis was based on a Lorentzian fit of single rotational-vibrational lines for 12 CO 2 and 13 CO 2 within a spectral window of 2 cm −1 providing parts per billion sensitivity for the determination of the absolute 13 CO 2 concentration.…”