Can a repeatable particle result still be misleading?
Yes. Repeatability does not rule out biased sampling, inappropriate dispersion or an unsuitable size definition. Review the complete measurement method, not just repeated scans of the same sample.
A useful investigation separates the material selected for testing from the way it was dispersed and measured. Changing several steps at once makes the cause harder to identify. Keep the original result and conditions, then compare one defined change using representative portions and the same reporting basis.
Ten error areas to check
- Sampling bias
- Unrepresentative sample division
- Unsuitable dispersion
- Inconsistent size definitions
- Incorrect sample amount
- Ignored measurement tolerances
- Assumed oversize sensitivity
- Misread distribution density
- Mixed number, volume or intensity weighting
- Undocumented procedures
How can a lab locate a sampling error?
Start with the same prepared portion and repeat its measurement. Then divide fresh portions from the bulk material and prepare each independently. If the fresh portions scatter more widely, investigate division and dispersion before adjusting the analyzer.
Method details to record
| Consideration | What to record |
|---|---|
| Sampling from one location | Collect increments across the bulk material to account for segregation |
| Taking a convenient scoop | Divide the laboratory sample reproducibly before choosing the test portion |
| Changing the dispersion state | Check for remaining agglomerates or unintended particle breakage |
| Comparing different dimensions | State which particle dimension each method reports |
| Using an unsuitable test amount | Select a loading appropriate to the sample and instrument |
| Overlooking method variability | Estimate the variation between independently prepared portions |
| Expecting detection of every rare particle | Check whether the sampled quantity and method can reveal the fraction of interest |
| Misreading distribution density | Check the size intervals and axis scale before comparing peak heights |
| Mixing distribution bases | Identify whether results are weighted by number, volume or intensity |
| Leaving the method undocumented | Record preparation, measurement and evaluation steps in the laboratory procedure |
Which report details can hide an apparent difference?
Check whether both reports show density or cumulative values and use the same weighting. A change from a number distribution to a volume distribution can make a coarse fraction appear more prominent even when the particles are unchanged.
Explore particle characterization equipment
Review the equipment details and discuss the supported configuration for your sample.