Abstract
In this whitepaper, we provide some helpful tips on how to develop a robust method that will deliver reliable and reproducible data, efficiently, every time it is used. ISO13320, the standard for laser diffraction places considerable emphasis on the importance of method development, arguably ‘the last expert task’ associated with laser diffraction, and there is a wealth of helpful information in the public domain. Here we focus on what you really need to know to develop a new method, to troubleshoot if things go wrong, and the tools that can be helpful.
Introduction
Particle size defines the performance of a wide range of different products, including cement, paints, inks, metal powders, cosmetics, foods and drinks. Measuring relevant particle size data is therefore essential in many industries, with laser diffraction usually the technique of choice. Fast, highly automated and suitable for measurement across a broad size range, 0.01 to 3500 μm, modern laser diffraction systems have reduced particle sizing to a matter of sample loading and push button operation, providing that a suitable method is in place.
Control sampling
Sampling, the first step in any analysis, is now the greatest potential source of error for a laser diffraction measurement. Exerting control at this stage is essential to measure representative data. Obtaining a representative sample from a larger bulk is a key challenge with any laboratory-based particle characterization technique. With modern laser diffraction particle size analyzers sampling is now the greatest potential source of error, especially when measuring large particles and/or when the specification is based on size parameters close to the extremes of the distribution. This is because the technique is volume-based and consequently extremely sensitive to small changes in the amount of coarse particles within a sample. The effect of sampling on reproducibility increases with particle size and with the width of the size distribution, as the volume of sample required to ensure representative sampling of the coarse particle fraction increases. For this reason, it can become necessary to measure a relatively large sample (often greater than 1-2 g) in order to ensure reproducible results. Further detailed discussion of sampling, a topic in its own right, is beyond the scope of this paper but Sampling for particle size analysis [2] is a great source of information for those requiring more detail.>> Download the full Application Note as PDF
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