Challenges of Assessing Number-based Particle Concentration and the Development of a Quantitative Method using DCS

Analytik reports on a poster presented at the Royal Society of Chemistry’s Formulation Science and Technology Interest Group’s Particle Dispersion in Liquid Formulation.

The Formulation Science & Technology (FST) and Particle Technology (PC) interest groups of the Royal Society of Chemistry organised a conference on Particle Dispersion in Liquid Formulations which took place virtually on 16th December 2020.

The meeting was based on the premise that for many liquid formulations which include particles, the final state of the particles is not just determined by classic colloid science particle dispersion considerations, but also by a number of other factors.  Rarely are fluid flows so intense in liquid formulations that primary particles are broken up. The initial state of agglomeration of multiple primaries, their break-up in the fluid flow and potential coagulation through process, storage and application are all important in determining the final state of the formulated product and thus its properties. For coatings and inks they determine the final colour / opacity and other functional properties, for food they influence mouth feel, for cosmetics they influence skin feel, for drugs they influence efficacy etc..

For more information about the event and presentation recordings, please visit: https://www.formulation.org.uk/partliq-home.html

Number-based particle concentration is an important attribute of industrial particle formulations which enable assessment of product batch-to-batch variability, and measurement of dosage for therapeutic and medical applications. However, its measurement accuracy and precision remain a challenge to industry due to the lack of relevant reference materials and standards. Collaboration between OxSonics and NPL has resulted in the development of a method to measure number-based particle concentration using Differential Centrifugal Sedimentation (DCS), with lower variability than reported by Particle Tracking Analysis (PTA).

Challenges of assessing number-based particle concentration and the development of a quantitative method using DCS – View poster

Beth A. Hinchliffe¹, Annhelen Lu², Mohammed Alkattan², Caterina Minelli¹
1 National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW
2 OxSonics Therapeutics, The Magdalen Centre, Oxford Science Park, Oxford, OX4 4GA

DCS can be used to analyse particle size distribution. The technique utilises a modified version Stokes’ Law to determine an unknown distribution of particle sizes by measuring the time it takes for particles to settle from a known distance in a liquid of known viscosity and density.

Exposure to high g-force through a centrifuge allows the sedimentation of even very small particles down to just a few nanometres in size to occur quickly, enabling real-time analysis.

The CPS Disc Centrifuge allows the measurement of highly poly-dispersed particles within an approximate size range of 3nm to 60 microns depending on particle density; the CPS can measure particles with as little as 2% size difference from one another. Rather than rely on a predictive algorithm, the CPS physically separates particles and measures them as they pass a light source detector.