NIR results of unground samples better reflect true actual variation in every
sample of any given product. They have a more accurate value for the original
sample/product than the analytical results from ground samples. Let me explain
why.
Most people accept a single analytical result as absolute and representative
of the consignment or production batch. There is often not an understanding of
the true variation that occurs within a product.
To get the most value from an analysis and decide on actions based on the
results, it is important to know the actual variation that can occur for that
specific product and also the factors that can contribute to variable analytical
results.
Recently, an extensive analytical exercise was conducted on a large amount of
raw materials and final products to evaluate the variations that exist and
factors causing those variations within these products/ingredients.
A large representative sample was taken from each product. Each sample was
well mixed and 50 different unground portions of that sample were scanned
separately on a NIR analyzer and also sent to an accredited laboratory for
analyses of all relevant components.
From the data it was concluded that the NIR results for the various
components were much more repeatable (lower standard deviation) and therefore varied less than
the laboratory’s chemical results.
A major reason for this can be due to the fact that the variation created in
the laboratory due to grinding and other steps in the analytical process has
been eliminated when analysing unground samples through the NIR.
To further demonstrate the effect of grinding, repeated chemical analyses
were also done on a small portion of ground samples. This would illustrate how
the actual nutrient content of a ground sample will vary from its original
unground sample after performing all the normal steps (including grinding)
during the chemical analytical process.
When the chemical results of these ground samples were compared to each other
an expected smaller variation was experienced than with the unground samples due
to the more homogenous nature of the final sample at the time when it was
analysed just after grinding.
In practice however, the greater variation experienced in the laboratory
results on unground samples is not, as often believed, a reflection of poorer
sample representation due to less homogeneity.
Because the unground samples are analysed "as is", the difference to ground
values actually indicates the undesirable variation that is created as a result
of additional handling and grinding of the original sample before analyses.
Therefore, unground samples are more representative of the true actual
variation that exists in every sample of any given product and is therefore a
more accurate value to be used for the original sample/product than the
analytical value that is reflected by ground samples.
Another advantage with NIR analyses is that a much larger portion of the
sample is scanned on the NIR, which results in a better representation of the
whole sample or batch.
Human error of handling, weighing and various other analytical handling
procedures are also not present in NIR analyses.
Finally, it must be noted that some NIR equipment also require grinding
before product can be analysed, which will result in similar problems
experienced during the wet chemistry process in that the result will not
represent the true value of the original product.
Author: Dr Hinner Köster
