Measurement sieve methods

Various grades of sorbitol are available that differ in their pcuticle size distribution. Most of the particle size measurements reported for sorbitol are by sieve methods [1,7,26,27], and permit direct comparison with the vendor s specifications. For the samples used in this study, the vendor specified sieve limits for the various grades are listed in Table 1. 

The best method of the determination of the particle size distribution of the different crospovidone types is the light diffraction measurement (e.g. Malvern Master Sizer, see Fig. 63 and 64). The particle size distribution of normal crospovidone also can be measured by sieving or air jet screening. In this dry sieving method more than 50 % of the particles are coarser than 50 pm without any swelling. Therefore even with this dry method it corresponds clearly to the definition of Type A of the Ph.Eur. monograph. 

The third shortcoming centers around the need for a good method for the determination of stable aggregates. The wet-sieve method, now commonly used, is generally recognized to be far from satisfactory. This is illustrated by the experiments of Harris et al. (1963), discussed below and shown in Fig.16.1. If a method had been used that measured true stable aggregates, as occur in nature, the values obtained would doubtless have been zero, or near zero, instead of values ranging up to 100%.. 

The size of particles in a sample can be measured by microscope analysis or by the use of a set of sieves. Typically, a sample of particles is passed through a set of vibrating sieves arranged with downward decreasing mesh diameters. The mass of particles retained on each sieve is measured. This method is quick and sufficiently accurate for most purposes. 

Analyzed by ultrasonic sieving method Measured by nitrogen adsorption method... 

AppHcations of soHd-state nmr include measuring degrees of crystallinity, estimates of domain sizes and compatibiHty in mixed systems from relaxation time studies in the rotating frame, preferred orientation in Hquid crystalline domains, as weU as the opportunity to characterize samples for which suitable solvents are not available. This method is a primary tool in the study of high polymers, zeoHtes (see Molecular sieves), and other insoluble materials. 

An alternate method for predicting the flood point of sieve and valve plates has been reported by Kister and Haas [Chem. Eng. Progi , 86(9), 63 (1990)] and is said to reproduce a large data base of measured flood points to within 30 percent. It applies to entrainment flooding only (values of Flc less than about 0.5). The general predictive equation is... 

The major gaseous components were analyzed by a gas chromatograph equipped with a TCD and a molecular sieve 13X column. The specific surface areas of carbon produced were measured by the BET method(ASAP 2010, Micromeritics). The morphology and particle size of the formed carbon were investigated by the scanning electron microscopy(S-4200, Hitachi... 

The dynamic methods involve the placement of particles to be measured in an environment which is subsequently disturbed. The members belonging to the particle set react differently to these imposed environmental impulses. These different reactions are observed and therefrom deductions are made as regards the size characteristics. As examples of dynamic methods mention may be made of sieving, streaming, elutriation, and sedimentation. 

Various techniques and equipment are available for the measurement of particle size, shape, and volume. These include for microscopy, sieve analysis, sedimentation methods, photon correlation spectroscopy, and the Coulter counter or other electrical sensing devices. The specific surface area of original drug powders can also be assessed using gas adsorption or gas permeability techniques. It should be noted that most particle size measurements are not truly direct. Because the type of equipment used yields different equivalent spherical diameter, which are based on totally different principles, the particle size obtained from one method may or may not be compared with those obtained from other methods. 

The most common method for measuring bulk density is to pour the powder into a tared graduated cylinder and measure the bulk volume (Vb) and mass of the material. Other methods, however, have been employed to ensure reproducibility, and a standard procedure has been reported [62,64]. For this testing, a sample of 50 g is passed through a U.S. Standard No. 20 sieve and is poured into a 100-ml graduated cylinder. The cylinder is then dropped from a height of 1 inch onto a hard surface three times at 2-second intervals. The volume of the powder is then read and used to calculate the bulk density. This three-tap method was found to give consistent results between laboratories. 

The frozen-drop technique was naturally adopted in measuring molten metal droplet size before any other methods became available. Similarly to the methods for normal liquids, the freeze-up and collection of molten metal droplets may be carried out in many different ways. For example, metal droplets can solidify during flight in gaseous or liquid medium in a spray chamber. 13H51 The solidified particles are subsequently sieved to obtain the size distribution. 

In the method, a weighed portion of a sample of coke dried at 110°C (230°F) and crushed to pass a No. 200-mesh sieve, mixed with stearic acid, and then milled and compressed into a smooth pellet. The pellet is irradiated with an x-ray beam and the characteristic x-rays of the elements analyzed are excited, separated, and detected by the spectrometer. The measured x-ray intensities are converted to elemental concentration by using a cahbration equation derived from the analysis of the standard materials. The K spectral lines are used for aU the elements determined by this test method. This test method is also apphcable to the determination of additional elements provided that appropriate standards are available for use and comparison. 

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