Sieve analysis analytical technique

Particle size is one of the principal determinants of powder behavior such as packing and consolidation, flow ability, compaction, etc., and it is therefore one of the most common and important areas of powder characterization. Typically, one refers to particle size or diameter as the largest dimension of its individual particles. Because a given powder consists of particles of many sizes, it is preferable to measure and describe the entire distribution. While many methods of size determination exist, no one method is perfect (5) two very common methods are sieve analysis and laser diffraction. Sieving is a very simple and inexpensive method, but it provides data at relatively few points within a distribution and is often very operator dependent. Laser diffraction is a very rapid technique and provides a detailed description of the distribution. However, its instrumentation is relatively expensive, the analytical results are subject to the unique and proprietary algorithms of the equipment manufacturer, and they often assume particle sphericity. The particle size distribution shown in Figure 1 was obtained by laser diffraction, where the curves represent frequency and cumulative distributions. 

Sieving is probably the most widely used and abused method of particle size analysis because the equipment, analytical procedures and basic concepts are so deceptively simple. Its popularity is due the relative simplicity of the technique, low capital investment and low level of expertise required to carry out the analyses. Sieve analysis presents three major difficulties [1]. With woven wire sieves, the weaving process produces three-dimensional apertures with considerable tolerances, particularly for fine-woven mesh [2]. The mesh is easily damaged in use [3]. The particles must be efficiently presented to the sieve apertures. 

CGE is suitable for the analysis of synthetic polyelectrolytes. Fast separations of high repeatability-when analyte interactions with the capillary wall are excluded-help to decrease separation time and solvent consumption compared with SEC. The only restriction is that CGE is only an analytical technique for small sample sizes. Selection of the optimal separation system with respect to molecular mass of the sieving polymer and its concentration is possible by applying simple rules and available data like intrinsic viscosity of potential sieving polymers. Non-UV-absorbing polyelectrolytes can be analyzed by applying indirect detection techniques. In various applications it has been shown that determination of molecular mass averages and molecular mass distribution is possible with CGE. 

Specificity is the most important requirement in gas analysis. Techniques dependent on the physical properties of the gas molecules, such as thermal conductivity, density, viscosity, and sound velocity, generally have insufficient specificity to differentiate a single gas in a mixture of gases, and therefore must incorporate in the procedure some type of preliminary separation. Vapor phase fractionation (gas chromatography) is an example of a popular analytical technique based upon a physical property (thermal conductivity) of the gas that requires preliminary separation of the gases by means of special columns (molecular sieve, silica gel, etc.). 

This sample handling and preparation scheme has been subjected to various tests, and proved to result in reproducible spectral signals (see e.g., Dabakk et al, 1999). As suggested by Malley Williams (1997), the sample could be sieved prior to NIR analysis in case the sediment contains coarse grained particles (>2 mm). Apart from the possible effects of grinding, the sample preparation and the subsequent NIR-analysis is non-destructive. This means that the sample can be used for further physical, chemical or biological analyses using conventional analytical techniques. 

We also described the different analytical techniques used to characterize powders both in terms of their size and composition. To determine particle size it is necessary to choose a method that has sufficient sensitivity. Sieving is a low-cost method and is reliable when the particle size is greater than about 60 pm. But if the particles are smaller than this, as is often the case, then the use of light scattering or X-ray diffraction should be considered. In determining both particle size and chemical composition it is essential that the specimen we choose for analysis is representative of the entire powder sample. 

This particle size control methodology should be monitored with an appropriate analytical technique. This is typically done with either a laser scattering based approach, by means of a sieve analysis of the milled material, or by means of a microscopic examination. It should be noted that each technique can result in a very different measured particle size distribution, because of the different fundamental properties that are observed by each technique. The differences of each technique are outlined elsewhere. 

Soil and molecular sieve adsorbent samples must be degassed for analysis. Useful analytical results may be obtained by simply heating the sample in an air-tight system and driving the evolved gases into the gas chromatograph. However, this technique does not yield very reproducible results, a limitation which is sometimes minimised by the analysis of several replicate samples. 

A second analytical measurement of protein purity, which should be conducted, is HPLC analysis. Various chromatography columns can be utilized to verify the purity of the protein. The most commonly employed methods are ion exchange chromatography, molecular sieve chromatography (also known as gel permeation chromatography), and hydrophobic interaction chromatography (HlC). Each of these techniques probe a different chemical aspect of the protein and provide excellent independent check of purity and homogeneity. 

Capillary zone electrophoresis is not only the simplest form of CE, but also the most commonly utilized. Discussion of this mode permits the presentation of a generic design for the instrumentation for CE. The addition of specialized reagents to the separation buffer readily allows the same instrumentation to be used with the other modes mentioned in the previous section addition of surfactants with MEKC, ampholines for CIEF and a sieving matrix (linear polymers, entangled matrices) for CGE. The discussion on CZE in the following subsections allows for analysis of some of the basic principles governing analyte separation by this technique. 

---