Is it possible for someone to explain the best way to interpret the distribution obtained from the CPS disc centrifuge.
Typically I would expect the following for PSD: D[v,0.1] value indicates that 10% of the particles are smaller than that size and therefore that the D[v,0.9] value indicates that 90% of the particles are smaller than that size. However recently obtained data from the disc centrifuge has given data which indicates the opposite. Is this to be expected for this equipment?
According to the protocol for particle size distribution by centrifugal sedimentation (CPS) ⁴, the CPS Disc Centrifuge separates particles by size using centrifugal sedimentation in a liquid medium. The particle concentration is measured by transmitted light intensity: when particles approach the outside edge of the rotating disc, they scatter a portion of a light beam that passes through the disc. The change in light intensity is continuously recorded, and converted by the operating software into a particle size distribution using Stokes law and assuming spherical particles.
The protocol also states that the D [v,0.1] value indicates that 10% of the particles are smaller than that size and therefore that the D [v,0.9] value indicates that 90% of the particles are smaller than that size. This is consistent with your expectation.
However, if you obtained data that indicates the opposite, it might be due to some factors such as:
- The sample preparation: the suspension should be dilute, cloudy but not opaque, and well dispersed using suitable wetting and/or dispersing agents. An ultrasonic treatment is useful in breaking up loosely-held agglomerates.
- The instrument calibration: the instrument should be calibrated using a standard suspension of known particle size and density before each measurement. The instrument should also be checked for proper balance and alignment.
- The data analysis: the operating software should be set with the correct parameters such as particle density, refractive index, viscosity, and optical properties of the medium. The data should also be corrected for any background noise or baseline drift.
(1) Protocol Particle size distribution by centrifugal sedimentation (CPS). https://www.epfl.ch/labs/lmc/wp-content/uploads/2018/06/CPS_E.pdf.
(2) CPS Disc Centrifuge | CPS Instruments Europe l cpsinstruments.eu. https://www.cpsinstruments.eu/cps-disc-centrifuge.
(3) CPS Instruments | Particle Size Analysis. https://cpsinstruments.com/.
(4) Our Products | CPS Instruments. https://cpsinstruments.com/products/.
(5) Data interpretation for CPS disc centrifuge? | ResearchGate. https://www.researchgate.net/post/Data_interpretation_for_CPS_disc_centrifuge.
(6) Differential Centrifugal Sedimentation Particle Size Analysis - Intertek. https://www.intertek.com/analysis-differential-centrifugal-sedimentation/.
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