Richard Bartlome

High-temperature multipass cell for infrared spectroscopy of heated gases and vapors

We present a novel design of a high-temperature multipass cell for laser-based spectrometers. Its performance is demonstrated with mid-infrared spectral measurements on hot bands of methane and on condensed compounds in the vapor phase.

Laser-based human breath analysis: D/H isotope ratio increase following heavy water intake

Following the ingestion of only 5.1 mL of D2O, a mid-infrared laser spectrometer determines the D/H isotope ratio increase in exhaled water vapor for the first time, to the best of our knowledge. This increase is still detectable several weeks after the heavy water intake. Collected breath samples are directly transferred into a high-temperature multipass cell operated at 373 K. No breath sample preparation is required. Aside from the capability to hinder unwanted condensation, measurements at elevated temperatures offer other advantages such as a lower temperature dependence of the delta value or the possibility to vary the intensity of absorption lines. We lay the foundation for many laser-based clinical applications. As an example, we measure a total body water weight of 55.2%+/-1.8% with respect to the total body weight, in agreement with the normal value of the male population.

Vapor-Phase Infrared Laser Spectroscopy : From Gas Sensing to Forensic Urinalysis

Numerous gas-sensing devices are based on infrared laser spectroscopy. In this paper, the technique is further developed and, for the first time, applied to forensic urinalysis. For this purpose, a difference frequency generation laser was coupled to an in-house-built, high-temperature multipass cell (HTMC). The continuous tuning range of the laser was extended to 329 cm(-1) in the fingerprint C-H stretching region between 3 and 4 microm. The HTMC is a long-path absorption cell designed to withstand organic samples in the vapor phase (Bartlome, R.; Baer, M.; Sigrist, M. W. Rev. Sci. Instrum. 2007, 78, 013110). Quantitative measurements were taken on pure ephedrine and pseudoephedrine vapors. Despite featuring similarities, the vapor-phase infrared spectra of these diastereoisomers are clearly distinguishable with respect to a vibrational band centered at 2970.5 and 2980.1 cm(-1), respectively. Ephedrine-positive and pseudoephedrine-positive urine samples were prepared by means of liquid-liquid extraction and directly evaporated in the HTMC without any preliminary chromatographic separation. When 10 or 20 mL of ephedrine-positive human urine is prepared, the detection limit of ephedrine, prohibited in sports as of 10 microg/mL, is 50 or 25 microg/mL, respectively. The laser spectrometer has room for much improvement; its potential is discussed with respect to doping agents detection.

Infrared laser-based sensing in medical applications

Laser-spectroscopic applications in medicine increase in importance. We present two medical applications of laser-based analyses of trace gases. The analysis of exhaled breath concerns the determination of the D/H isotope ratio after intake of a small amount of heavy water. The D/H isotope ratio can be used to deduce the total body water weight and lays the foundation for many other laser-based clinical applications. An elevated D/H ratio could be monitored in breath samples up to 30 days after ingestion of only 5 ml of D2O. A second example concerns the analysis of surgical smoke produced in minimally invasive laparoscopic surgery with electroknives. The quantitative determination of harmless and hazardous compounds down to the ppm level is demonstrated. A specific example is the presence of sevoflurane at concentrations of 80 to 300 ppm, an anesthetic, which to our knowledge is measured for the first time in an abdominal cavity.

Optoacoustic detection of different doping substances commonly used by athletes with an optical parametric generation laser source

In this paper, we present first results of a spectral characterisation of doping substances using a resonant optoacoustic cell and a Nd:YAG laser pumped optical parametric generation (OPG) laser source in the mid-infrared wavelength range between 3.0 and 4.0 μm with periodically poled LiNbO3 as nonlinear medium for the frequency conversion. Single spectra covering a wavelength range of about 220 nm can be conducted within less than 2 hours (3s averaging time, 7s between consecutive data points, about 0.3nm step-width). Despite the large linewidth of the OPG source of 240 GHz (8 cm-1), the laser spectrometer is well suited for the spectral analysis of these large organic molecules as they exhibit structured continuum absorption over a wide spectral range rather than isolated absorption peaks. We present measured spectra of ephedrine, alprenolol, ethacrynic acid, etc. and discuss the potential of laser-based detection of doping substances both as a supplement to existing methods and in view of a fast in situ screening technique at sporting events.

First laser-based determination of deuterated water vapor in human breath

Following the ingestion of only 5 mL D2O, an infrared laser spectrometer determines the D/H isotope ratio increase in exhaled water vapor for the first time. No preliminary breath sample preparation is required.