Agriculture Reference
In-Depth Information
SubSAMPLInG In THE LAborATory
When the submitted sample arrives at the seed laboratory, it is entered into the oficial log, assigned a
number and the accompanying information is recorded. The sample then goes to the subsampling area of
the laboratory, where it is divided into a working sample for the various tests that will be performed. The
remaining portion is retained as an oficial or ile sample in case future tests are desired. The weight of the
working sample for purity analysis is determined by the weight of the seed required to comprise a minimum
of 2,500 seeds and will vary greatly in size and weight from small- to large-seeded species. The sample size
needed for a noxious weed test is ten times as much as that needed for purity analysis, e.g., 25,000 seeds.
The Importance of Subsampling
Dividing procedures must be absolutely precise and unbiased if the test results are to be meaningful. The
working sample must accurately represent the sample submitted to the laboratory, which in turn represents
the seed lot only if proper sampling procedures were properly followed.
Subsampling Techniques
The AOSA Rules for Testing Seeds state that the working sample shall be taken from the submitted sample
in such a manner that will result in a representative sample. The actual procedure may be either by manual
or mechanical methods. Several hand methods are used, including the hand-halving and hand mixing or
spoon method.
Mechanical halving devices, also called dividers (Figure 3.6), are most often used for subdividing
and are dependable for providing representative samples. These are devices that divide the sample into two
equal portions, both in size and content. The working sample is obtained by dividing the submitted sample
one to several times until the proper weight of the working sample is obtained. Any of the divided portions
may be combined and redivided to yield the proper-sized working sample.
Figure 3.6. Subsampling dividers: on the left is a Gamet Precision divider, in the middle is a Boerner divider,
and on the right is a chaffy grass rifle divider.
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