Laser-spectrometric gas analysis: CO₂–TDLAS at 2 µm

Abstract

View the article online for updates and enhancements. Related contentMetrological quantification of CO in biogas using laser absorption spectroscopy and gas chromatography Javis A Nwaboh, Stefan Persijn, Karine Arrhenius et al. Abstract Employing direct absorption spectroscopy and using a spectrometer comprising a single-pass and a multipass white cell, we probed the R(12) line of carbon dioxide (CO 2 ) in the combination band around 2 μm. Gravimetric gas standards containing CO 2 , between 300 and 60 000 μmol mol −1 (0.03% to 6%), in N 2 were quantified by means of the TILSAM method. The spectrometric results were compared with the gravimetric reference values. We describe our implementation of the 'Guide to the Expression of Uncertainty in Measurements' to infrared laser-spectrometric gas analysis. Data quality objectives are addressed by uncertainty and traceability flags. Uncertainty budgets are presented to show the quality of the results and to demonstrate software-assisted uncertainty assessment. The relative standard uncertainties of the spectrometrically measured CO 2 amount fractions at, e.g., ambient levels of 360 μmol mol −1 and at exhaled breath gas levels of 50 mmol mol −1 were 1.4% and 0.7%, respectively. Our detection limit was 2.2 μmol mol −1. The reproducibility of individual results was in the ±1% range. Furthermore, we measured collisional broadening coefficients of the R(12) line of CO 2 at 4987.31 cm −1 . The relative standard uncertainties of the measured self-, nitrogen-, oxygen-and air-broadening coefficients were in the ±1.7% range.

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

“…[10] showed that uncertainty figures do not suffer when CO2 and H2O amount fraction measurements are combined by scanning the laser wavelength over two neighboring CO2 and H2O absorption lines. Here, the relative expanded uncertainties were estimated as 2 % to 3 % for nominal amount fractions of 100 μmol/mol, documenting a slight improvement for CO2 upon the earlier work [17]. Finally, ref.…”

The gas temperature compensation research based on TDLAS technology

“…Among them, the tunable diode laser absorption spectroscopy technology (TDLAS) has become one of the core technology of gas detection. TDLAS has been widely applied in the fields of air pollutants detection, environmental supervision, commercial manufacture and the source of energy and electricity, for its high sensitivity, short response time , non-contact measurement and so on [1] [2] . However, due to the dependency between the absorption line type and temperature of the gas, the absorption line intensity and line width will change with the change of the temperature and the concentration of the gas, which has a direct impact on the line type and amplitude of the second harmonic signal and therefore brings about the measurement error.…”

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

“…Traceability in absolute, laser-based amount fraction measurements is feasible and described by the TILSAM protocol [4]. 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.…”

“…time) to wavenumbers. The latter is derived from the transmission curve of laser light passing through a Fabry-Pérot etalon [17]. The absorption line area is retrieved via a non-linear least squares fit of the absorbance spectrum using an appropriate line profile (e.g.…”

“…For example, ref. [17] reported measurements from 60 mmol/mol to 360 μm/mol CO2 in N2 gas mixtures and yielded relative expanded uncertainties in the range 1.4 % to 2.8 %, respectively. A study presented in ref.…”