Focused beam reflectance measurement method

Since the inherent growth rate of many organic compounds is relatively slow, addition times may be long in order to achieve supersaturation control within the metastable zone. Higher addition rates can result in nucleation and the creation of a bimodal distribution. Experimentation to determine acceptable addition rates can be evaluated by focused beam reflectance measurement (FBRM) and other in-sim, online methods (Chapter 2) or microscopic observation of the crystal slurry which could reveal the presence of fines. These issues are highhghted in the examples below. 

Su et al. [24] studied the polymorphic transformation of n-mannitol by in situ Raman spectroscopy coupled with FBRM (focused beam reflectance measurement) and PVM (particle vision measurement). In this way, relationships between fine particles and metastable-form dissolution, and also between coarse particles and stable-form crystallization, could be defined. The different polymorphs were identified by Raman spectroscopy. FBRM provided a method for independently verifying these observations. PVM, in turn, verified the data interpretation strategy employed for FBRM. 

In addition to the characterization of the product, the characterization of the system during the crystallization process may be very important as it may help to ensure a stable and controlled crystallization process leading to material of the desired quality. A number of methods have been adapted for online use. These include XRPD, IR, ultrasound absorption, and Fraunhofer diffraction. The most commonly and conveniently used ones are turbidity, NIR, Raman, FBRM (focused beam reflectance measurement), and PVM (particle vision measurement). 

Along with the ever increasing demand for on-line or in-line particle characterization in process control, requests for direct measurements of particles in pipelines or reactors are on the rise. In process control, any bias of the characterization method or precise physical meaning of the parameters determined are not of the utmost importance. Robusmess, reliability, and precision of measurement are often the primary concerns. Besides focused beam reflectance and fiber optical PCS probe, back scattering intensity measurement is among the optical techniques preferred for in-process measurement due to the obvious reasons that when the concentration of a suspension is high, the... 

The coil (wound on a light metal former) can be suspended by a fine strip of phosphor bronze between the pole pieces. Attached to this suspension is a small mirror which reflects on to a scale a beam of light which is focused upon it. An instrument of this kind is known as a D Arsonval galvanometer and is used in potentiometer circuits and various methods of measurement of resistance. 

Fig. 6. Experimental arrangement for lifetime measurements by the phase-shift method, using laser excitation. The laser beam is amplitude-modulated by a Pockel cell with analysing Nicol prism and a small part of the beam is reflected by a beam splitter B into a water cell, causing Rayleigh scattering. This Rayleigh-scattered light and the fluorescence light from the absorption cell are both focused onto the multiplier cathode PMl, where the difference in their modulation phases is detected. (From Baumgartner, G., Demtroder, W., Stock, M., ref. 122)).

This is a technique used to measure the IR adsorption or reflection spectra of very small samples. In this method, a sample is placed on a KBr disc and a microscope is then used to focus the IR beam onto Ae material. 

Another method of measurement of diffuse reflectance does not require an integrating sphere. In this method, the sample beam is focused onto the sample by means of ellipsoidal or spherical mirrors and collected by another ellipsoidal mirror, at either 180 or 90° from the incident beam. This method has been used for many years in the infrared, since proposed by Fuller and Griffiths (1978, 1980). The advantage is very high collection efficiency and the ability to measure very small samples. Such geometry is known by a number of names, including biconical, Praying Mantis (a trade-... 

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