Particle size, measurement laser diffraction

Photon correlation spectroscopy (PCS), also referred to as dynamic light scattering, is a technique that is used to measure particles in the size range of 1 -0.001 p,m. Unlike particle sizing by laser diffraction, the sample, dispersed in a diluent, is not circulated, stirred, or sonicated during the measurement. The technique is dependent upon a stable suspension of particles that are in constant random motion due to collisions with molecules of the suspending liquid. 

Particle Size Measurement. The best way to evaluate an emulsion s stability is probably to measure its particle size distribution. A number of methods are available for droplet size determination (see Sec. VIII.A). Optical microscopy, although a time-consuming technique, is a direct way of measuring droplets larger than 1 pm. Nowadays, laser lightscattering, diffraction, and transmission methods are becoming popular for routine determination of particle size [151, 152],... 

Laser diffraction equipment, in particle size measurement, 18 153—154 Laser diffraction methodology, 23 193—194 Laser diodes, 14 699 22 172, 173-176. 

By electron microscopy the size of the primary particles in the aggregates is estimated to be about 10 nm. Particle size measurements using a nanosizer show the size of aggregates dispersed in a well wetting solvent to be in the range of 100 nm. Laser diffraction of fumed silica dispersed in air provides sizes of agglomerates larger than 5 pm. 

Starch gelatinization up to peak viscosity studied by various techniques such as vis-cometry and particle size measurement by laser diffraction, is essentially a first order kinetic process whose extent is determined principally by pasting temperature and time (Kubota et. al., 1979 Lund, 1984 p. 59 Okechukwu et al., 1991 Okechukwu and Rao, 1995). 

Sensors for particle size characterization used for crystallization include ultrasound attenuation measurement/ " laser diffraction/ and laser backscatteiing/ commercially called focused beam reflectance measurement (FBRM). Ultrasonic attenuation spectroscopy has been used to monitor the crystallization process parameters such as the crystal size distribution, concentration, and the onset of nucleation during batch crystallization of L-glutamic acid/ Off-line laser diffraction has been used to measure the crystal size distribution in the development of the crystallization process for a pharmaceutical intermediate/ ... 

In addition,there are several experimental options available for particle size measurement alone. They include single particle optical sensing (SPOS), laser diffraction (LD), and ultrasound attenuation (UA). 

Figure 7 (a) Inhalation measurement cell with Malvern Spraytec laser diffraction analyzer, combined with Andersen cascade impactor (76). (b) Time-history showing the mean particle size measured during the actuation of the Clickhaler containing the micronized (M-SX) and supercritically produced (S-SX) salme-terol powders in formulation with lactose and at the airflow rate 49 L/min. 

Figure 6.5 SEM of a micronized powder and particle size measured by laser diffraction.

Figure 7-12 Distribution of the equivalent size of spherical and non-spherical particles obtained by laser diffraction measurements and a microscope, a) polystyrene spheres, b) copper particle, c) aluminum oxide...

Particle agglomerate sizes can be determined using a laser diffraction particle size analyzer, such as a Brinkmann PSA-2010. With this instrument, the principle of particle size measurement is based on various light scattering angles generated by paiTicles of... 

The particle size distribntion of microcapsules can also be measured using laser diffraction particle sizing, Mastersizer andZetasizer. For microcapsules prepared for inhalation, particle size measurement of the dry powders formnlated can be measured more accurately by the dry dispersion method. The Scirocco accessory of the Malvern Mastersizer allows particle size measurement of dry powders, with particle flow controlled by a variable feed-rate vibrating tray. 

Particle size measurement techniques (Fig. 1) with various higher dispersion energies at very low (time-of-flight method) and at high silica aerosol concentrations (cascade impactor, laser diffraction method with air-jet injection) seem to be a powerful tool to investigate particle interactions. 

Terray [4] examined laser diffraction as a method for the in-line measurement of particle size, and examples of the application of Insitec laser granulometers developed by Malvern Instruments are described. These include their use for particle size measurement in the cryogenic grinding of plastics. 

Nathier-Dufor et al. Comparison of Sieving and Laser Diffraction for the Particle Size Measurements of Raw Materials used in Food Stuffs, Powder Technology, 76 (1993) 191-200. 

Merkus [136] gives a thorough discussion of the possible error sources related to laser diffraction particle size measurements. An outline of such error sources are provided below ... 

The surface mean diameter is the diameter of a sphere of the same surface area-to-volume ratio as the actual particle, which is usually not a perfect sphere. The surface mean diameter, which is sometimes referred to as the Sauter mean diameter, is the most useful particle size correlation, because hydrodynamic forces in the fluid bed act on the outside surface of the particle. The surface mean diameter is directly obtained from automated laser light diffraction devices, which are commonly used to measure particle sizes from 0.5 to 600 p.m. X-ray diffraction is commonly used to measure smaller particles (see Size TffiASURETffiNT OF PARTICLES). 

The particle size analyzer, based on laser light diffraction, consists of a laser source, beam expander, collector lens, and detector (Fig. ] 3.45). The detector contains light diodes arranged to form a radial diode-array detector. The particle sample to be measured can be blown across the laser beam (dry sample), or it can be circulated via a measurement cell in a liquid suspension. In the latter case, the beam is direaed through the transparent cell. 

This is a universally applicable instrument for determining particle-size distributions of all kinds of solids which can be analysed either in suspension in a measuring cell or dry by feeding through a solid particle feeder. In the Fritsch Analysette 22 laser diffraction apparatus the measured particle-size distribution is displayed on the monitor in various forms, either as a frequency distribution, as a summary curve or in tabular form and can be subsequently recorded on a plotter, stored on hard disk or transferred to a central computer via an interface. The time required for one measurement is approximately 2min. 

Methods for analysis of the particle size distribution in the aerosol cloud include techniques such as time of flight measurement (TOE), inertial impaction and laser diffraction. Dynamic light scattering (photon correlation spectroscopy) is confined to particles (in suspension) in the submicron range. In addition to the size distribution, the particle velocity distribution can be measured with the Phase Doppler technique. 

Laser diffraction is a fast alternative for analysis of the size distribution of particles in an aerosol cloud. The theory of laser diffraction is well understood [124,125]) but this technique requires special measures to test inhalation devices and to interpret the results correctly. One of the major problems is that flow adjustment through the inhaler is not possible. Furthermore, the presence of carrier particles from adhesive mixtures may disturb the measurement of the fine drug particles and the size distribution obtained is of an unknown dehvered mass fraction of the dose. These practical problems and limitations have been solved by the design of a new modular inhaler adapter for the Sympatec laser diffraction apparatus (Figure 3.6). 

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