Optical fibre probes

The application of near-IR spectroscopy for real-time monitoring of glucose, lactic acid, acetic acid and biomass in liquid cultures of microorganisms of the genera Lactobacillus and Staphylococcus has been recently published [76]. The NIR spectrum acquired by the optical-fibre probe immersed in the culture is exploited using a partial least squares (PLS) calibration step, a classical method for IR techniques. 

M. Olazar, M.J. San Jose, S. Alvarez, A. Morales, J. Bilbao, Measurements of particle velocities in conical spouted beds using an optical fibre probe, Ind. Eng. Chem. Res. 37 (1998) 4520 4527. 

Molecular beacons (MBs) are hairpin-shaped oligonucleotides that report the presence of specific nucleic acids. The MBs have been immobihzed by Tan and co-workers [27] onto ultrasmall optical fibre probes through avidin-biotin binding. The MB-DNA biosensor detected its target DNA molecules, in real time, with selectivity for a single base-pair mismatch. This MB-DNA-biosensor was used by Perlette and Tan [28] for real-time monitoring of mRNA-DNA hybridization inside a living cell. 

Optical fibre probe. ATR is used for the study of samples at a distance from the optical bank of the apparatus through the use of suitable optical fibres, that is,... 

Meanwhile, several important developments have been recently proposed either for instruments and accessories (for example, diode array spectrophotometers or optical fibre probes) or for spectra exploitation (for example, chemometric software). These improvements have led to a lot of applications, based on the exploitation of a large part of the UV spectrum. 

UV-Vis process analysers can be used in a noncontact mode as the source radiation can be passed though a window in a process pipe, for example, and the emitted radiation detected on the other side of the pipe. This means that the sample can be subjected to a measurement without its flow being impeded or its composition changed in any way. Optical fibres are used to transmit the radiation to and from the sample, which can be in a distant location, a hazardous area or in a harsh environment such as a high temperature reaction vessel. The most common forms of optical fibre probes used for UV-Vis measurements are of the transmission and ATR types (Figure 9.12). The petroleum and chemical industries use UV-Vis spectroscopy for monitoring many of their processes ... 

The Raman technique has been readily adapted for on-line process analysis, especially in the pharmaceutical industry ". It has the benefits of mid IR, e.g. the ability to identify compounds from the vibrational fundamentals, without the constraints of mid IR, e.g. the limitations of the optical materials that can be used. Its popularity is also due in part to the excellent throughput of optical fibres for the radiation required for Raman, i.e. in the Vis and NIR regions. This use of optical fibre probes (Figure 9.14) facilitates easy in-line analysis because the sample can be remote from the instrumentation, even to hundreds of metres in distance. Fibre optic multiplexers are also available, allowing many samples to be analysed sequentially. Small laser diode sources and CCD detectors can be attached to the optical fibres and changed as required, rendering the overall device small and flexible. Radiation from the laser diode light source is transmitted to the sample by optical fibre... 

Narayanaswamy, R., Sevilla F., An Optical Fibre Probe for the Determination of Glucose Based on Immobilized Glucose Dehydrogenase , Anal. Lett. 21 (1988) 1165-1175. 

Figure 2.15. Optical fibre probe foam analysis showing schematic representations of (a) the foam analyser (b) the fibre tip with light reflected in the gas and liquid phases (c) the events which take place when the probe is moved through a foam. In the latter, the path of the probe and the chord lengths are shown at the top, while in the middle and at the bottom, respectively, the analog and digitized signals are shown (from ref. (12)), with permission from Elsevier Science...

Full NIR spectra of a set of 74 neat polymer additives, measured with an optical fibre probe and taken in diffuse reflectance mode, have been used for qual-... 

In churn-turbulent flow, in the core of the column the bubble velocity and chord length distributions are alike at different radial positions, but in the wall region they are very different from the core of the column. A few reports on the application of optical fibre probes for phase holdup measurements in three-phase fluidized beds have be found, in which the local bubble frequency, the local phase holdups and the local bed porosity were measured [108, 159, 177]. Time-average local gas holdups and bubble frequency were measured independently by an optical fiber probe. 

Razzak SA, Baighi S, Zhu J-X, Mi Y (2009) Phase holdup measurement in a gas-liquid-solid drculating fluidized bed (GLSCFB) riser using electrical resistance tomography and optical fibre probe. Chem Eng J 147 210-218... 

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