Ethylene and CO2 emission rates and pathways in harvested fruits investigated, in situ, by laser photothermal deflection and photoacoustic techniques

Abstract

CO2 laser photothermal deflection (limit 1 nl I-') and photoacoustic detection (limit 6 pl I-') systems were used to measure ethylene emission rates from point sources of a wide range of mature nonclimacteric and climacteric fruits. In addition, an infrared gas analyzer was used to measure CO2 from the same samples. As well as total rates, the percentages emanating from the skin, tissue at the distal end (floral scar) and the pedicel were established. Possible links with fruit behaviour during abscission are discussed.

Multi-gas sensing based on photoacoustic spectroscopy using tunable laser diodes

“…Sensitivity for HCl was a little worse, due to the lower optical power injected into the PA. A detection limit of only 3 ppm of HCl in nitrogen was reached in the present configuration. Detection limit for H 2 O has not been measured at this time, but a value of approximately 0.2 ppm of H 2 O in nitrogen has been estimated from the sensitivity obtained for CH 4 . A reduction of the residual background noise is expected in the future by proper acoustic isolation, and a sub-ppm detection limit for the three hydrogenated compounds (in nitrogen) is expected.…”

“…Schematic representation of our experimental set-up for the measurement of CH 4 , H 2 O and HCl using three near-infrared DFB lasers and a PA cell operated in its first longitudinal resonance. Lasers for CH 4 and H 2 O are fibre-coupled and their emission is directly launched into the PA cell using a fibre collimator. Laser for HCl detection is used in free-space configuration.…”

“…6 and shows a good linearity. From the noise level, a sensitivity of 0.5 ppm (corresponding to a signal-to-noise ratio SNR = 1) is obtained for CH 4 detection in nitrogen with an average laser power of 10 mW and using the small R c = 3 mm resonator. The detection limit of CH 4 in pure helium is reduced to 2 ppm, due to the much smaller cell constant (see Fig.…”

“…Detection limit for H 2 O has not been measured at this time. However, a value of approximately 0.2 ppm of H 2 O in N 2 is estimated from the sensitivity obtained for CH 4 and taking into account the ratio of the absorption coefficients of the corresponding absorption lines and the different laser power.…”

“…A precise monitoring of a large variety of species in different gas mixtures and at various concentration levels, ranging from parts per billion (ppb) to several hundreds of parts per million (ppm), is required in various fields of applications. Relevant domains include, for example, atmospheric researches [1], combustion processes [2], medical diagnostic by breath analysis [3], food industry [4] or pollution monitoring [5]. Industrial process control is also of great importance, as extremely high purity gas mixtures are usually employed and level of impurities or contaminants must be precisely controlled at trace levels.…”