Skip to content

Colorado Seed Lab Purity

The Purity Process


The first step in a purity test is dividing.  This ensures a non-discriminate sample of roughly 2500 seeds for this test.  Most kinds of seeds have predetermined weights that equal near that quantity.  The Gamet Divider mechanically divides samples in half again and again using centrifugal force.   Sometimes seeds are too big, too fragile or too fluffy for the mechanical divider, so we divide these things by hand.  Shown here is the pie method.  The sample is divided into halves and halves again to attain the proper weight.

Sample Separation

A purity board is the surface used to make a separation of a large portion of seed.  Pure seeds are scraped into the drawer, and other components are left on top for further analysis.  A blower can be used to separate components of a sample based on density.  The light-weight material (chaff, empty seeds, light inert material etc.) will blow over the top and into a collection cup, while the heavier material (full seeds, rocks, sticks etc) will stay in the lower portion.

Taking a closer look

A binocular scope is used to get a closer look at a sample.  Light from the top allows the analyst to see the external features of the seed while light from the bottom provides a view through the seed components to help determine purity.

Final separation and identification

The goal of the purity process is to separate the sample into pure seed, other crop, weeds and inert material categories.  The other crop and weeds all need to be properly identified for the test.  Our seed library or herbarium, contains positively identified seeds of hundreds of species of seeds of both crops and weeds.  All weeds found in a sample need to be determined as common or noxious, and if noxious, restricted or prohibited, so we use our herbarium to double check a positive identification.

Weights and Measures

Once all of the components are verified, each part is weighed and recorded.  A purity report can now be generated.  If a germination test is requested, the pure seed moves on to be planted.




Leave a Comment

Contact CSU Equal Opportunity Privacy Statement Disclaimer

2018 Colorado State University, Fort Collins, Colorado 80523 USA