Particle Sizing Methods

The sizing methods involve both classical and modem instrumentations, based on a broad spectrum of physical principles. The typical measuring systems may be classified according to their operation mechanisms, which include mechanical (sieving), optical and electronic (microscopy, laser Doppler phase shift, Fraunhofer diffraction, transmission electron miscroscopy [TEM], and scanning electron microscopy [SEM]), dynamic (sedimentation), and physical and chemical (gas adsorption) principles. The methods to be introduced later are briefly summarized in Table 1.2. A more complete list of particle sizing methods is given by Svarovsky (1990). 

Sieving is the simplest and most widely used technique for powder classification. This method is based only on the size of the particles and is independent of other particle properties (e.g., density, optical properties, and surface roughness). 

The common sieves are made of woven wire cloth and have square apertures. The sizes of the sieve openings have been standardized, and currently two different sets of standard series, the Tyler Standard and the U.S. Series ASTM Standard, are used in the United States. The mesh number of a sieve is normally defined as the number of apertures per unit area (square inch). Thus, the higher the mesh number the smaller the aperture. Typical mesh numbers, aperture sizes, and wire diameters are given for the lyier sieves and the U.S. ASTM sieves in Table 1.3. Sieve analysis covers the approximate size range of 37 pm to 5,660 pm using standard woven wire sieves. Electroformed micromesh sieves extend the range down to 5 pm or less while punched plate sieves extend the upper limit. 

Mesh no. Tyler standard U.S. series ASTM standard  

Microscopy is often referred to as an absolute method for the determination of size and size distribution of small particles because it allows direct visualization and measurements of individual particles. Three commonly used types are optical microscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). 

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Comparison of Results From Four Particle Size Methods. 

This account of the kinetics of reactions between (inorganic) solids commences with a consideration of the reactant mixture (Sect. 1), since composition, particle sizes, method of mixing and other pretreatments exert important influences on rate characteristics. Some comments on experimental methods are included here. Section 2 is concerned with reaction mechanisms formulated to account for observed behaviour, including references to rate processes which involve diffusion across a barrier layer. This section also includes a consideration of the application of mechanistic criteria to the classification of the kinetic characteristics of solid-solid reactions. Section 3 surveys rate processes identified as the decomposition of a solid catalyzed by a solid. Section 4 reviews other types of solid + solid reactions, which may be conveniently subdivided further into the classes... 

TTiere are several particle sizing methods, all based upon sedimentation and Stokes Law. If a particle is suspended in a fluid (which may be gas, or any liquid), the force of resistance to movement by the particle will be proportional to the particle s velocity, v, and its radius, r, vis-... 

Many solid-liquid reactions are likely to benefit from the careful selection of the reactant (particle size, method of manufacture, etc.). Many reaction-crystallization systems may benefit from the use of seed crystals (see Section 5.4). 

Methods for making both forms solvent-soluble were the subject of many patents and closely guarded industrial secrets, but much of the mystery was cleared up in two papers by Gerstner [23] and Smith and Easton [24] published in 1966, by which time X-ray diffraction, electron microscopy and disc centrifuge particle sizing methods had been brought to bear on the problem. 

Agut et al. (2011) assessed the different technology transfer options and reported that within Sanofi-Aventis that option 1 (comparative testing) is the approach of choice for critical methodologies, i.e. assay, degradation products, and in some cases water content and dissolution. Option 2 (co-validation) is reserved for less-critical methodologies, i.e. residual solvents by gas chromatography (GC), water content, dissolution and particle size methods whereas, option 4 (transfer waiver) is restricted to pharmacopoeial compendial methods, i.e. appearance, pH, particulate matter, etc. 

Microscopy remains the principal standard method of particle sizing and of shape and morphological classification. Though often tedious and time consuming in its application, it remains a standard by which individual particles can be classified with confidence and most particle sizing methods are referenced. 

Hillbrick G.C., McMahon D.J., Deeth H.C. 1998. Electrical impedance particle size method (Coulter Counter) detects the large fat globules in poorly homogenized UHT processed milk. Aust. J. Dairy Technol. 53, 17-21. 

Particle Size Method of Method of Damage in in Microns Treatment Measurement Microns Ref. 

Detection limit, quantification limit, accuracy, and specificity are not normally considered appropriate for validation of particle sizing methods. 

The author of these recommendations added that the validation of particle sizing technique cannot be completed with the first batch of a sample, as data are insufficient to fully validate the procedure at this stage. It is not always important to know the absolute particle size of the first batch manufactured, but it is important to know how the second and subsequent batches compare with it. The validation of a particle size method should be in phases, with parts completed when the first sample is analyzed and other data completed or added later, for example, prior to the regulatory filing. Calibration or verification of an instrument being used is assumed to be normal part of GMP and may be used as a suitability assessment. " ... 

This paper focuses on the application of two particle sizing methods, laser diffraction spectroscopy and ultrasonic attenuation spectroscopy, to the characterization of suspensions of filmed powders. 

In most applications more than one particle is observed. As each individual may have its own particle size, methods for data reduction have been introduced. These include the particle-size distribution, a variety of model distributions, and moments (or averages) of the distribution. One should also note that these methods can be extended to other particle attributes. Examples include pore size, porosity, surface area, color, and electrostatic charge distributions, to name but a few. 

ESTIMATION OF AVERAGE PRIMARY PARTICLE SIZE METHOD OF CHARACTERISTIC TIMES... 

Esrinuirion of Average Primary Particle Size Method of Characteristic Times 347... 

Estimation of Average Primary Particle Size Method of Characteristic Times 346 Primary Particle Size Effects of Aerosol Material Properties 350 Particle Neck Formation 353 Particle Crystal Structure 355 Basic Concepts 355 Experimental Obsetyafions 355 Problems 356 References 357... 

Polydispersed aerosols are used for the efficiency-by-particle size method. Upstream and downstream measurements are made using optical particle counting devices at a variety of flow rates. The dust-holding capacity of a filter is a measurement of the synthetic dust loaded onto a filter under established procedures and a measurement of the pressure drop as the loading increases. 

Increasing interest in detailed experimental analysis of two-phase flows has led to a number of review papers on single point laser measurements. A more general overview on two-phase flow measurements was given for example by Taylor (1994) focusing on current activities in PDA development and PIV applications in two-phase flows. Applications of LDA and PDA for analyzing flows with combustion were reviewed by Heitor et al. (1993), and a more industrial orientated review on particle sizing methods can be found in Black et al. (1996). 

The specific, particle sizing method chosen depends on the type of. size information needed and the chemical and physical properties of the sample. In addition to the three techniques discussed here, molecular sieving, electrical conductance, microscopy, capillary hydrodynamic chromatography, light obscuration counting, field-flow fractionation, Doppler anemometry, and ultrasonic spectrometry-are commonly applied. Huch of the particle sizing methods has its advantages and drawbacks for particular samples and analyses. 

Before choosing a particle sizing technique, examination of the samples under a microscope is usually wise becau.se the range of sizes and shapes present can then he estimated. Most particle size methods are sensitive to particle shape and all are limited with respect to the particle size range. Particles with approximately spherical shapes are measured most accurately. Needles and other shapes that differ significantly from spherical are often analyzed by microscopy. 

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