Tunable Laser Absorption Spectroscopy System Research Articles

Detection of methyl mercaptan with a 3393-nm distributed feedback interband cascade laser

Attention has been focused recently on the harmful effects and malodor of methyl mercaptan (CH3SH), so it is desired to detect CH3SH in situ, sensitively, and selectively. We detected methyl mercaptan via tunable laser absorption spectroscopy (TLAS) with a room-temperature distributed feedback interband cascade laser emitting around 3393 nm and a hollow waveguide gas cell with 5 m length. The fundamental characteristic fingerprint absorptions of CH3SH from 3260 to 3400 nm were examined, and the spectral line 3393.584 nm (corresponding to the ν2 C–H symmetric stretch) was determined to be the optimum for CH3SH detection. The response characteristics of the TLAS system were established by implementing a set of CH3SH concentration gradient experiments with wavelength-scanned direct absorption spectroscopy. The results show that CH3SH TLAS spectra are in excellent agreement with spectra from the Pacific Northwest National Laboratory database; the TLAS response linearity is 0.987, and the detection limit is as low as 25 ppbv (parts per billion by volume, 10−9) with integrated time 1.84 s, corresponding to an absorbance of 1.34 × 10−4 (near the theoretical detection limit). Overall, the TLAS system is a robust method for CH3SH monitoring of industrial waste gas emissions.

Nitric oxide breath testing by tunable-diode laser absorption spectroscopy: application in monitoring respiratory inflammation.

We used a high-resolution mid-IR tunable-laser absorption spectroscopy (TLAS) system with a single IV-VI laser operating near 5.2 microm to measure the level of exhaled nitric oxide (eNO) in human breath. A method of internal calibration using simultaneous eNO and exhaled CO2 measurements eliminated the need for system calibration with gas standards. The results observed from internally calibrating the instrument for eNO measurements were compared with measurements of eNO calibrated to gas standards and were found to be similar. Various parameters of the TLAS system for eNO breath testing were examined and include gas cell pressure, exhalation time, and ambient NO concentrations. A reduction in eNO from elevated concentrations (approximately 44 parts in 10(9)) to near-normal levels (<20 parts in 10(9)) from an asthmatic patient was observed after the patient had received treatment with an inhaled glucocorticoid anti-inflammatory medication. Such measurements can help in evaluating airway inflammation and in monitoring the effectiveness of anti-inflammatory therapies.