Andreasen pipette
An Andreasen pipette is a glass laboratory device used in physical chemistry . It is used to determine the grain size distribution of particles up to a size of approx. 1 μm and is named after Alfred Andreasen . The method belongs to sedimentation analysis and is used in process engineering and the like. a. used in the pharmaceutical industry.
principle
The particles to be examined (e.g. a powder ) are first suspended in a suitable liquid and distributed evenly.
Initially, it can be assumed that the suspended particles are equally concentrated in all transverse layers of the suspension. As time progresses, however, the particles sediment, with the larger particles sedimenting more quickly than the smaller ones , according to Stokes' equation . A modification of the above Equation, the descent rate equivalent diameter can be determined at any given sedimentation time.
The Andreasen pipette has a device for withdrawing the liquid and a scale that provides information about the filling level of the liquid, so the height of the liquid level after each sample withdrawal and the withdrawal time result in a rate of descent that can be equated with the rate of descent in Stokes' equation is. After a change, the modified equation results:
or.
The size d is called the sinking velocity equivalent diameter and, during the measurement, depends on the height of fall (or liquid level) h and the time t of the sampling - thus every h and t has a certain particle diameter, which represents the maximum particle size in the sample volume. The sample volumes are then evaporated and the mass of the respective residue is determined in order to create a run-through sum curve for further evaluation.
The validity of Stokes' equation is decisive for evaluable data, which must be ensured with a Reynolds number Re <0.2 (area of creeping flow). Furthermore, the substance to be examined must neither swell, dissolve nor chemically change in the dispersing liquid.
literature
- Alfred N. Martin (founder), Hans Leuenberger (revision), Ottheinrich Eichhorst and Michael Lanz (collaboration): Martin Physikalische Pharmazie. Physico-chemical principles applied pharmaceutically. 4th edition, Wissenschaftliche Verlagsgesellschaft, Stuttgart 2002, ISBN 3-8047-1722-5
Individual evidence
- ↑ AHM Andreasen and JJV Lundberg: An apparatus for determining the fineness using the pipette method with a special focus on operational inspections . In: Reports of the German Ceramic Society. Volume 11, 1930, pp. 312-323. For Alfred (Herman Munch) Andreasen (June 1, 1896– March 2, 1978) see: JC Poggendorffs biographical-literary concise dictionary for mathematics, astronomy, physics with geophysics, chemistry, crystallography and related fields of knowledge. Volume 6, Part 1, Berlin 1936, pp. 54-55; Volume 7b, Part 1, Berlin 1967, pp. 84-85; Volume 8, Part 1, Berlin 1999, pp. 94–95 (with further references and list of works).
- ↑ Alfred N. Martin (founder), Hans Leuenberger (revision), Ottheinrich Eichhorst and Michael Lanz (collaboration): Martin Physikalische Pharmazie. Physico-chemical principles applied pharmaceutically. 4th edition, Wissenschaftliche Verlagsgesellschaft, Stuttgart 2002, ISBN 3-8047-1722-5 , Chapter 16: Powder and agglomerate systems. Sedimentation analysis section . Pp. 634-636.