Examination of Particulate Matter an Filter Membranes

Journal/Book: Reprinted from Nature Vol. 183 p. 1000 only; April 4 1959. 1959;

Abstract: ´Shell' Research Ltd. Thornton Research Centre P.O. Box 1 Chester. Feb.26. FINE filter membranes with maximum pore sizes lass than 1µ are now readily available for collecting solid material suspended in a liquid. As the membranes are of very uniform thickness they may be examined under a microscope for the determination of the sizes and nature of the particles deposited an them. We have used a simple and effective technique for preparing slides incorporating the sample membrane. The essential feature of the method is that the membrane is made transparent to permit the use of transmitted light without disturbing the particle distribution. A water ejector pump is usually used to assist filtration. By keeping this running the membrane may be dried in a few minutes. With the suction still applied a fixative is poured down the side of the filter funnel so as to spread steadily across the membrane and be drawn through it. The forces acting an the particles are such that these are held against the membrane and are not disturbed by the advancing liquid front. The fixing process is complete when the fixative has been drawn through the membrane and the latter is again dry. With the correct choice of fixative the membrane retains its porosity and is thus capable of being rendered transparent by saturation in Canada Balsam diluted with xylene. It can be mounted as desired without fear of disturbing the particles. We have used a solution of 0·5 per cent (w) ´Perspex' in chloroform as the fixative and found it to be eminently suited to our application. Where an automatic particle counter is used care must be taken to choose a membrane exhibiting negligible grain when treated and to ensure that the drying processes are carried to completion otherwise blotches caused by trapped air or liquid other than Balsam may result in counting-errors. We wish to thank the Directors of ´Shell' Research Ltd. for permission to publish this communication. ___MH

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