Read everything about the acquisition of Quantachrome by Anton Paar here

Representative Sampling

Is the entire size distribution represented in the small scoopful you just put into your analyzer?  Probably not, unless you split the original sample on a Rotary (spinning) Riffler.

Particle Segregation

Large particles roll over smaller particles, as in this heap of coal.

It is often found that divided solids (powders, granules, etc) segregate by size when they are agitated or shaken. Small particles tend to collect towards the bottom of the container, larger ones on top (the so-called “Brazil Nut Effect”. Heaps tend to accumulate larger particles towards the outside as they roll over smaller particles. Therefore, when taking sub-samples it is important to eliminate the effects of such segregation. If this precaution is not taken, the results of particle sizing, surface area measurements and, at times, porosity measurements can be severely biased. When inaccurate results are scaled up to industrial sized applications, entire processes can fail to achieve their desired end results.



Good Sampling Practice

Large particles “rise” to the top of a shaken container
(the “Brazil Nut Effect”)

The “Golden Rules” for sub-sampling put forth by Allen [1] simply state that the sample(s) should be taken when the powder is in motion (i.e. a powder stream), and the entire cross section of the entire stream shall be sampled many times. If this is not done when the container is loaded, it should surely be done when the container is emptied. A Rotary Riffler does just that.


A Superior Sampling Device
The superior performance of rotary riffling over all other methods of powder sampling is demonstrated by the data below [1]:

Sampling Device Est. Maximum Error (%) 
Cone and quarter  22.7
Scoop  17.1
Table splitter 7.0
Chute splitter 3.4
Rotary riffler 0.42 


When compared to the random variation of 0.075, the rotary riffler is clearly superior, and should be used whenever possible [1], and is probably the best instrument available for the subdivision of powders having heterogeneous particle-size distributions[3], and produced the smallest overall inaccuracy levels of five protocols assessed for splitting soil samples [4].

[1] T.Allen (1981) Particle Size Measurement , 3rd ed, Chapman & Hall.
[2] A.A.Khan (1968) MSc Thesis, Bradford University
[3] H.G.Brittain (2002) Pharm. Tech., July ‘02, 67-73 [external link]
[4] R.W.Gerlach et al (2002) J. Chemometrics, 16 , 321-328

  Scoop sampling a fine powder selectively removes material from an already segregated mass.

Instruments for Representative Sampling

Rotary splitting (spin riffling) conforms to the Golden Rules of Sampling.

Anton Paar offers the Quantachrome Micro Rotary Riffler, automated representative sampler. For more details click here.