Vapor zone velocities measurement using a capillary optical fiber sensor with an application to gas chromatography

Description of the response of a fiber optic velocity sensor applied to capillary gas chromatography

“…Fig. 1 shows that this frequency increases with time, because the vapor zone accelerates, due to a decompression of the helium carrier gas [1]. One can also observe that the amplitude of the oscillation decreases with time, from about 7% of the average signal at the beginning to less than 1% at the end.…”

“…2. In our previous studies [1], the emphasis was mostly on the position of the velocity peak, on the abscissa; here, the focus will be on the height of this peak, on the ordinate.…”

“…Hereafter, this optical fiber will be referred to as the capillary fiber. The operating principle of the sensor, which is polarization modes coupling caused by a rotation of birefringence axes induced by vapor absorption in the stationary phase, and the first results of velocities measurement, permitting the identification of the analytes, have been published recently [1]. The present paper is instead focused on the quantitative aspect of the sensor's signal.…”

“…In this paper, we present results of a theoretical modeling of the mode coupling mechanism that forms the basis of the operational principle of the migration velocity sensor that was presented earlier [1]. The sensor, initially developed for capillary gas chromatography (GC), is a distributed fiber optic sensor that measures the velocity of vapors zones in real time, as they migrate inside the capillary.…”

“…All of these fiber optic sensors are not distributed sensors, and once decoded, the information provided by these detectors is not much different from those of other detectors used in GC: they measure the amount of analyte passing in the detector over time. The polarimetric sensor that we developed [1,[6][7][8][9][10] differs from the previous ones in that it is really a distributed sensor. Light is injected at the entrance of the capillary fiber, propagates along the entire length of the capillary, where it interacts with the analyte present in the column, and is then detected at the capillary output.…”