03/17/2005 • Analytics • Focus on Products at Analytica

Qualifying of Particle Sizing Instruments by Particle Standards

Particle sizing instruments do have a hard life. They have to operate all the time and they have to give correct particle size distributions under all circumstances. But what could one expect from such an instrument really? In fact that it simply works. Not more!

If one demands more then that a particle sizing instrument has to be qualified. This means it has to be proofed (and documented) that the instrument is working correctly and that it measures data which are very close to the "true values". This will be assumed as mandatory by all quality concepts and organizations like e.g. DIN ISO, GMP/GLP, ASTM, PMA, FDA, ISPE... for any used scientific instrument of a quality control department.

How can I qualify a particle sizing device? Well, this depends on my expectations due to the typical task the instrument has to perform.
I have to validate wether these tasks will be accomplished by the instrument or more precisely what are the differences between my expectations and the measurable results.
To realize this it is worth to apply particle size standards which have been characterized by the manufacturer very carefully. The indicated mean diameters normally are traceable to national authorities like the National Institute of Standards and Techchnology (NIST) and documented in the accompanying certificate.

As a first step it is important to determine the precision of the measured diameters by comparing them with the data of the certificates. A second test should show how repeatable these results are and a third test how reproduceable they are under different measuring conditions, e.g. different "warming-up-periods", sensitivity adjustments, flow rates, etc. A very important item to look at is the size resolution which reflects the capability to distinguish and to detect similar particle diameters. It can be established by preparing binary or ternary mixtures of particle size standards and applying them under observation wether the resulting peaks will be detected as separated single peaks or just as one broadened signal.
In some cases a further quality criteria could be the resolution of relative quantities of particle numbers or volumes/masses.

This test and other qualification tests can be conducted by applying particle size or particle count standards as well.

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