Influence of Ethanol on Breath Acetone Measurements Using an External Cavity Quantum Cascade Laser

Abstract

Broadly tunable external cavity quantum cascade lasers (EC-QCLs) in combination with off-axis integrated cavity enhanced spectroscopy (OA-ICOS) provide high molecular gas sensitivity and selectivity. We used an EC-QCL in the region of 1150-1300 cm´1 in both broadband scan mode, as well as narrow scanning mode around 1216 cm´1, respectively, for detection of acetone in exhaled breath. This wavelength region is essential for accurate determination of breath acetone due to the relative low spectral influence of other endogenous molecules like water, carbon dioxide or methane. We demonstrated that ethanol has a strong spectroscopic influence on the acetone concentration in exhaled breath, an important detail that has been overlooked so far. An ethanol correction is proposed and validated with the reference measurements from a proton-transfer reaction mass spectrometer (PTR-MS) for the same breath samples from ten persons. With the ethanol correction, both broadband and narrowband molecular spectroscopy represent an attractive way to accurately assess the exhaled breath acetone. The importance of considering spectroscopic ethanol influence is essential, especially for the narrowband scans, (e.g., 1216 cm´1), for which the error in determining the acetone concentrations can rise up to 39% if it is not considered.

Sensitive Spectroscopy of Acetone Using a Widely Tunable External-Cavity Quantum Cascade Laser

“…Note that all of these three spectroscopy options are available with the same setup without any physical change in the source or other parts of the spectrometer. In comparison to OA-ICOS with ~1000 m effective interaction length [ 15 , 38 ], we obtain a similar sensitivity with WMS-2f and a multipass cell. In addition, the measurement time of the current WMS-2f system is substantially faster than OA-ICOS system.…”

“…However, the cost of MS instruments is very high, they need sample preparation and do not offer portable operation. Laser spectroscopy provides an alternative to MS methods with lower cost, portable operation, compactness and ease of use; which has been already employed (e.g., QCLs or EC-QCLs based systems) for acetone detection in human breath or its stand-off detection [ 38 , 48 , 53 , 54 ]. Acetone has broadband absorption features in the mid-infrared region with a large amount of closely spaced ro-vibrational transitions.…”

“…Other researchers followed for the detection of other gases using single or multiple molecular absorption lines [ 20 , 35 , 36 , 37 ]. However, achieving high sensitives for larger molecules via scanned WMS is still remain a demanding task [ 38 ].…”

Real-time breath gas analysis of CO and CO2 using an EC-QCL

“…The performance of narrowband WMS detection is comparable to recent EC-QCL-based WMS setups [8,9,12] and close to cavity-enhanced spectrometers [10,13]. The sensitivity was ultimately limited by fluctuations in the wavelength-dependent background caused by fringes.…”

“…Such external-cavity QCLs (EC-QCLs) also offer a large (~100 cm −1 ) mode-hop-free tuning range and high-bandwidth fine tuning via piezoelectric elements and laser injection current [1,5]. Consequently, EC-QCLs have been used for highresolution broadband absorption spectroscopy [6,7], as well as for sensitive narrowband detection in environmental, combustion and medical applications [8][9][10][11][12][13]. Given the high output power, EC-QCLs are also well-suited for photo-acoustic spectroscopy [14].…”