How many methods are there for sampling?

Laser diffraction particle size analysis is a process that characterizes the particle size distribution of a large number of substances by testing and analyzing a small number of samples. Representative and convincing measurement results are inseparable from a reasonable sampling process. Accordingly, sampling is the first and most important part. The sampling is a process of obtaining a “laboratory sample (10ⁿg)” from a “large amount of sample (10ⁿkg)”, and then obtaining a “measurement sample (10ⁿmg)” from the “laboratory sample”.

Acquisition of Laboratory Sample from the Process Stream: 

The best method of sampling from the process is to remove the sample from a flowing powder stream rather than from a static pile like a silo or a drum. If the only possibility is a static powder pile, samples should be removed from different positions and different depths in the pile or drum, which will be mixed to obtain a representative laboratory sample. 

Acquisition of Test Sample: 

Users can use a spinning riffler to acquire a representative test sample from the laboratory sample. A spinning riffler is a device that divides the laboratory sample into many fractions whose characteristic composition corresponds exactly to that of the original laboratory sample. Each fraction can be used as a test sample. If the fraction is excessive, it needs to be further split by the spinning riffler again to make sure that the entire subsample will be used for a single measurement. A spatula or spoon can be used to sample from the laboratory sample if the sample is held in a solid glass jar with a screw cap. However, the jar must be at least 30% empty to allow the rest of the powder in the jar (70% or less) to be tumbled for rehomogenization. The tumbling should be done seven times in succession before taking the sample from the jar. The jar must never be shaken as vibration creates stratification causing the user to sample coarse particles from the top of the jar. This will not be representative and will lead to a test producing a larger particle size analysis.

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