~ an Advanced Laboratory Imaging and Analysis System ~
Sample Size
ALIAS uses an optical process involving an optical scanner to measure particle dimensions. But several characterisitcs of the scanning process and of the particles that are scanned--especially the two-dimensional viewing geometry of three-dimensional particles, the roughness of particles which have jagged boundaries, and the displacement of particles from the centerline of the scanner--all set limits on the accuracy that can be achieved.
Accordingly ALIAS makes certain assumptions to maximize accuracy. One of those assumptions is that there'll be several particles present when it conducts a scan, and that they'll be scattered somewhat randomly over the scan area. Consequently discussions about ALIAS accuracy will always be in regard to the average measurements of a sizeable sample of particles, not to the measurements of individual particles.
ALIAS can scan a single particle, of course. If you choose to do so, note that the accuracy will generally be greatest if you align the long axis of the particle parallel with the long axis of the scanner glass, and if you place the particle close to the centerline of the scanner.
But ALIAS, when used as it's designed, should be shown at least 40 particles in a sample. You can of course run ALIAS with smaller samples, but ALIAS will warn you of that fact. ALIAS will also alert you if the sample is not randomly placed. ALIAS will also warn you when the standard error recommends a larger sample size than was present during the scan.
As a rule of thumb, Cascade Data Systems recommends sample sizes of about 200 particles. With practice, an experienced ALIAS user can distribute and separate 200 particles over the "large" scan area in a minute or so. As you gain more familiarity with how ALIAS measures a given species of catalyst, and as you understand the population of particles from which you draw your samples, you might adjust this desired sample size upwards or downwards.
Cascade Data Systems makes no assertions about the accuracy of ALIAS outside of its intended operating limits. Before using ALIAS outside of its intended use, it is strongly recommended that you thoroughly test ALIAS to ensure that it provides the level of results that you seek. And even then, Cascade Data Systems makes no assertions about the accuracy of ALIAS when operated outside of its intended operating limits.
