AbstractFiltration is defined as the separation of solid particles from a liquid or gas by passing the suspension through a porous, fibrous or granular substance. In science and industry, filtration is commonly used for the concentrating and/or removal of particulate matter or for the separation of particles into size classes for subsequent physical, chemical or biological analysis. Separation of particles into multiple size classes is often required for the assessment of particle size. There are many different types of filters available (e.g. fibrous, membrane, polycarbonate) for particle characterization through filtration. The type of filter to be used for particle size characterization is dependent on a number of considerations such as sample (particle) characteristics, collection efficiency, pore size and structure and analytical compatibility. Filtration has the advantage of being one of the few techniques which allow for the physical separation of particles into different size classes for distribution or chemical–biological analysis. If appropriate precautions are taken to minimize sample perturbations (e.g. select appropriate filter for the application, filter in the field, avoid overloading a filter, ensure a low flow rate and stir if possible), a reasonably accurate estimate of particle size can be obtained. Generally, errors associated with filtration arise from filter clogging and when attempting to characterize flocculated/aggregated particles. The basic nature of a suspended aggregate (i.e. fragile, plastic, high water content) means that it is likely to be broken up or created owing to the often tortuous nature of filtration, or be deformed on the surface or within the filter owing to pressure effects. This has implications if optical image analysis of the filter is to be used for particle size analysis as the true particle morphology and size will have been altered. In such an instance, if only a grain size distribution is required, it is suggested that optical image analysis be employed in conjunction with a plankton chamber settling technique rather than with filtration.
