Beckman Coulter LS 13 320, User Manual

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PN B05577AC B-8
Sample Handling
Solid Sample Dispersion
Solid Sample Dispersion
Solid sample dispersion is an attempt to disperse a dry powder with the intent of suspending it in
air. As previously mentioned, dry powders encounter problems with solubility, reactivity and
suspendibility, when suspended in liquid media. Due to these problems, analysis of dry systems is
quite often preferred. In many instances, selection of solid sample dispersion is dependent on the
end use of the product. For example, particle size measurement of flour must be carried out using a
dry system, hence requiring solid sample dispersion. Dry powders that are free flowing, anti-caking
and anti-clogging require no external dispersion aids. However, if these conditions do not hold true,
external dispersion aids (additives that have a much lower or distinguishable size from sample) such
as fumed silica (size ~1 nm), tricalcium phosphate, and carbon black are available. Fumed silica,
when added to particulate systems (0.5-1 wt%), can help the flow of the dry powder because of its
“ball-bearing” effect. The same mixing ratio (0.5-1%) can be used for tricalcium phosphate. Also, its
overall effect on particle size measurement can be negligible. Sometimes, anti-static aids such as
sprays and a static bar are needed to eliminate static charges.
Diluent Selection
Consider Solvation Effects
•
If the sample dissolves, it may be necessary to use a saturated solution to perform the
measurement.
•
If the sample does not dissolve, then this may be a good diluent.
Consider Other Effects
•
Does the diluent react chemically with the sample to alter the sample?
•
Does the diluent react physically with the sample to cause agglomeration, flocculation,
aggregation, clumping, etc.?
•
Does the sample shrink or swell in the proposed diluent?
Consider the Effects the Diluent Has on the Sample's Suspension Fluid
•
Does the diluent react chemically with the sample's suspension fluid?
•
Does the diluent and the sample's suspension fluid act together to cause agglomeration,
flocculation, aggregation, clumping, etc.?