Microplasma emission spectroscopy of carbon dioxide using the carbon monoxide Ångström system

Abstract

The present paper describes a system and method for indirect emission spectroscopy of CO2 in the visible spectrum. This is achieved by using a microplasma spectrometer that first converts CO2 into CO and then measures emissions from the CO Ångström system (B1Σ + → A1Π) at 560 nm. The experiments were performed on gaseous samples of CO2, mixed in both N2 and air, to concentrations between 0.01% and 100%. In addition to the microplasma spectrometer, the process was monitored by mass spectrometry with a residual gas analyzer. The CO2 to CO conversion efficiency was found to be very high, reaching a maximum of 41% at close to 100% selectivity. Furthermore, the CO Ångström system was shown to facilitate excellent spectroscopic measurement of CO2 concentrations below 10%, with a linearity of R2 > 0.99 and an expected limit of detection in the parts-per-thousands range. The most promising aspect of the results was that the analysis was performed on extremely small total sample amounts where the gas flow through the systems was in the 0.1 µmole/s range. Hence, the present system has the prospect of filling a void in current sensor technology, where inexpensive and easy-to-use optical systems, such as nondispersive infrared sensors, cannot handle small sample amounts, while mass spectrometers, which can handle such samples, still are expensive, complex, and bulky.

Partial least squares modelling of spectroscopic data from microplasma emissions for determination of CO2 concentration

“…We have previously reported a microplasma based system for optical emission spectroscopy of CO2 [4]. This system utilizes both the physics and the chemistry of the plasma, where CO2 first is converted to CO in a chemical process, after which optical emissions from the CO Ångström system are recorded by a spectrometer.…”

“…Even though the emission process is very specific, the conversion process is not, and may vary depending on the composition of the sample. For example, the conversion process was shown to be significantly influenced by the presence of O2 [4].…”

Compliance of a microstructured, soft sampling device for transcutaneous blood gas monitoring

“…The complete system is thoroughly described by Persson and Berglund. 19 Before a measurement began, the OES system was initialized and allowed to stabilize for >30 min. Then, the capillary was inserted into the patch, aer which the OES system was allowed to stabilize for another minute, before the patch was attached to one of the authors' lower arm with a piece of tape.…”

“…The data was recorded and analyzed by the same soware used by Persson and Berglund, 19 where the CO 2 content of the sample was estimated by studying the 0-3 band of the CO Angström system. The intensity of this emission bandcentered at 560 nmwas linearly dependent on the CO 2 content.…”

“…The intensity of this emission bandcentered at 560 nmwas linearly dependent on the CO 2 content. 19 The spectroscopic signal was extracted in three steps where, (i) the spectrum was ltered with respect to both wavelength and time with smoothing average lters of power 2 and 7, respectively, (ii) the background was subtracted by tting a fourterm Gaussian model to the spectrum in the wavelength interval 552-564 nm, but excluding points between 558 and 562 nm, i.e. the CO 2 -dependent interval, and (iii) the spectroscopic signal was then dened as the integral of the latter interval.…”