Particle Characterisation
How to perform fully automated static image analysis simply and accurately
Kai Dueffels, Retsch Technology GmbH,
technology@retsch.com
Imaging techniques are superior to traditional particle analysis methods in terms of information content and accuracy. Depending on the application, the particle size distribution can be based on the most appropriate size defi nition such as length, width, circle-equivalent diameter, stretched length, etc. In addition, only image analysis can determine and quantitatively describe important shape parameters like aspect ratio, circularity, or roundness. The laser diffraction technique only provides an equivalent diameter relative to a sphere model; in analytical sieving, the resolution of the distribution is limited to the sieves available, and the method is not reasonably applicable for samples in the lower micrometer range.
What is static and dynamic image analysis?
In particle characterisation, a distinction is made between static and dynamic image analysis. Dynamic image analysis is ideal for the routine analysis of bulk solids. Thanks to high sample throughput and low susceptibility to errors, this method is a great alternative to conventional sieve analysis.
Static image analysis is more likely to be used for narrow size distributions, with a focus on the precise characterisation of mostly fi ne particles. This method acquires high-resolution particle images which allow for size and shape measurement with highest accuracy. Static image analysis is based on a microscopic procedure in which a slide is photographed step by step and the particle images are evaluated automatically. With the CAMSIZER M1 Retsch Technology introduces a new analyser which is based on this principle.
How does the new CAMSIZER M1 work?
The CAMSIZER M1 (Figure 1) uses the principle of static image analysis to determine the particle size and particle shape. The fi ve different objective lenses of the analyser cover different size ranges so that an overall measuring range of 0.5 µm to 1500 µm is achieved. At the start of each measurement, the particle size / particle shape analyser CAMSIZER M1 determines the focal plane for the measurement area which ensures that all particle images in the selected area are pin-sharp (tilt compensation). All image data and measurement data are stored during analysis, providing manifold possibilities for subsequent data evaluation with the Particle X-Plorer software module. When the measurement is fi nished, an overview image gives the user a good idea of the particle quality. Particles stretching over more than one measurement fi eld can be pieced together by using the innovative stitching algorithm and may thus be evaluated although their size is larger than 1500 microns.
Technical Features • 18 Megapixel colour camera
• Five objective lenses: 2.5x, 5x, 10x, 20x, 50x • Illumination: transmitted light / refl ected light • Large sample stage (up to 8 standard slides) • High-performance dispersion module M-Jet
Application Example: Paracetamol
Static image analysis is ideal for the characterisation of fi ne pharmaceutical ingredients and excipients.
The CAMSIZER M1 software allows the evaluation of individual images and clear visualisation of single particle images. The distribution of the particle width, particle length and the circle-equivalent diameter can be put out separately.
Figure 1. CAMSIZER M1 with dry dispersion unit M-Jet.
Figure 2. Analysis of paracetamol with the CAMSIZER M1. Upper left: image acquired at 10 x magnifi cation, transmitted light. Upper right: Particles in the image are recognized and all relevant size and shape parameters are displayed. Clear and comprehensive graphical representation of the size distribution (lower left diagram) and the particle shape (lower right diagram). Measuring time: 9 minutes, number of images: 1600, number of particles: 120 000.
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