Irène Ventrillard

Frequency Comb Based Spectrometer for in Situ and Real Time Measurements of IO, BrO, NO2, and H2CO at pptv and ppqv Levels

We report an instrument designed for trace gas measurement of highly reactive halogenated radicals, such as bromine oxide and iodine oxide, as well as for nitrogen dioxide and formaldehyde. This compact and robust spectrometer relies on an alternated injection of a frequency-doubled femtosecond radiation at 338 and 436 nm into two parallel high-finesse cavities, for measuring BrO + H(2)CO, and IO + NO(2), respectively. The transmission of the broadband radiation through the cavity is analyzed with a high resolution, compact spectrograph consisting of an echelle grating and a high sensitivity CCD camera. The transportable instrument fits on a breadboard 120 × 60 cm size and is suitable for in situ and real time measurements of these species. A field campaign at the Marine Boundary Layer in Roscoff (in the northwest of France, 48.7°N, 4.0°W) during June 2011 illustrates the outstanding performance of the instrument, which reaches a bandwidth normalized minimum absorption coefficient of 1.3 × 10(-11) cm(-1) Hz(-1/2) per spectral element, and provides detection levels as low as 20 parts per quadrillion of IO in 5 min of acquisition.

Introduction to Cavity Enhanced Absorption Spectroscopy

In this introductory chapter we will begin with an historical outline of the development of cavity enhanced absorption methods, with just enough attention to the applications that either motivated them or became conceivable after their development. Given the number of publications in this domain, we will consider only the first demonstrations, and those works leading to substantial improvement or innovation in the state of the art.

Real-time measurements of endogenous carbon monoxide production in isolated pig lungs.

Abstract. Ischemia-reperfusion injuries are a critical determinant of lung transplantation success. The endogenous production of carbon monoxide (CO) is triggered by ischemia-reperfusion injuries. Our aim was, therefore, to assess the feasibility of exhaled CO measurements during the ex vivo evaluation of lungs submitted to ischemia-reperfusion injuries. Five pigs were euthanized and their lungs removed after pneumoplegia. After cold storage (30 min, 4°C), the lungs were connected to an extracorporeal membrane oxygenation circuit, slowly warmed-up, and ventilated. At the end of a 45-min steady state, CO measurements were performed by optical-feedback cavity-enhanced absorption spectroscopy, a specific laser-based technique for noninvasive and real-time low gas concentration measurements. Exhaled CO concentration from isolated lungs reached 0.45±0.19  ppmv and was above CO concentration in ambient air and in medical gas. CO variations peaked during the expiratory phase. Changes in CO concentration in ambient air did not alter CO concentrations in isolated lungs. Exhaled CO level was also found to be uncorrelated to heme oxygenase (HO-1) gene expression. These results confirm the feasibility of accurate and real-time CO measurement in isolated lungs. The presented technology could help establishing the exhaled CO concentration as a biomarker of ischemia-reperfusion injury in ex vivo lung perfusion.

A transportable spectrometer for in situ and local measurements of iodine monoxide at mixing ratios in the 10−14 range

We present a robust, compact, and transportable instrument that measures the iodine monoxide atmospheric radical at extremely low concentration, down to 40 ppqv (parts per quadrillion by volume, 1:1015). As nitrogen dioxide is strongly absorbed in the same spectral region it could be simultaneously measured down to 4 pptv (parts per trillion by volume, 1:1012). Relying on “mode locked cavity-enhanced absorption spectroscopy,” the instrument makes use of a free-running commercial femtosecond Titane Saphir laser. We demonstrate that this multiplex detection scheme provides shot noise limited spectra for acquisition times as long as 5 min. Moreover, this instrument is very versatile as it can be potentially tuned from the infrared to the ultraviolet (1080-340 nm) to reach various molecular absorptions. It has been recently deployed at the Station Biologique de Roscoff on the North West Atlantic coast of France.

Exhaled carbon monoxide is correlated with ischemia reperfusion injuries during ex vivo lung perfusion in pigs

Measurement of exhaled carbon monoxide (eCO) might help in the selection of lung grafts during ex vivo lung perfusion (EVLP) since its endogenous production is increased under ischemia reperfusion. The objective of this study was to measure eCO variations depending on the extent of lung ischemia reperfusion injuries. Using a porcine model and a laser spectrometer instrument, eCO was measured during EVLP. eCO was compared after 30 min (D0) or 24 h (D1) of cold ischemia. The ability of eCO to distinguish lungs deemed suitable for transplantation was evaluated. Six lungs were studied at D0 and compared to six lungs studied at D1. eCO was systematically higher on D1 (1.35 ± 0.26 ppmv versus 0.95 ± 0.31 ppmv, p = 0.01). The best threshold concentration for eCO to select lungs was 0.86 ppmv (area under the receiver operating characteristic curve: 0.65 [95% confidence interval: 0.34-0.97], p = 0.40). These results show that eCO varies during EVLP. The interpretation of this variation and the role of eCO as a biomarker of ischemia reperfusion injuries during EVLP should be tested in further clinical studies.

Nitric Oxide Analysis Down to ppt Levels by Optical-Feedback Cavity-Enhanced Absorption Spectroscopy

Monitoring nitric oxide at the trace level is required in a large range of applications. We report on a trace gas analyzer optimized for nitric oxide measurements by Optical Feedback Cavity Enhanced Absorption Spectroscopy with an interband cascade laser at 5.3 µm. The short response time of the instrument allows for reaching the level of 50 ppt in only 180 ms. Its stability enables averaging up to 12 min to reach a detection limit of 0.9 ppt. Absolute concentration calibration requires to account for the optical saturation effect that results from the intense absorption line intensity addressed here, in the mid infrared region, in contrast to instruments that are operating in the near infrared region.