Physical Purity Testing

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Physical Purity Testing Inquiry

Physical purity testing refers to the analysis for classifying the composition of a seed lot. It is important for evaluating whether the given seed sample conforms to the prescribed purity standards; and whether it can truly represent the seed lot.

Ideally, the working sample should roughly contain at least 2500 seeds. The components of the sample can be screened by naked eyes or using hand magnifiers, microscopes, or semi-automatic inspection stations. Usually, the working sample is separated into four parts (pure seeds, other crop seeds, weed seeds, and inert matters) by hand, blowers, or sieves; and the percentage of each component is then calculated by weight (Figure 1).

  • Pure seeds: portions of the working sample represented by the crop species being tested. The pure seeds portion includes all botanical varieties of that kind/species. It also includes immature, diseased, shriveled, damaged (>1/2 of the original size), or germinated seeds.
  • Other crop seeds: crop seeds other than the specific crop species being examined; usually less than 5% of the total sample weight.
  • Weed seeds: the portion of seeds that are recognized as weeds by laws, regulations or by general usage.
  • Inert matters: components that are not seeds, including materials like structures, stems, leaves, sand and stone particles, empty glumes, lemmas, paleas, chaff, awns, spikelets, and so on.

Figure 1. Classification of sample components in seed physical purity testing (Elias et al., 2012).

For tests that are conducted to determine particular components (e.g., noxious weeds) in the sample, the sample sizes are usually around 25000 seeds units, and the result calculation is based on the seed numbers, instead of weight, of specific components.

Lifeasible has rich experience and superior expertise of physical purity testing for variety of plant species, including grasses/forages, native seeds, canola, cereals, pulses, vegetables/flowers, and so on. Our advanced laboratories facilities and cutting-edge technologies ensure the quality and efficiency of our services. Aside from a broad range of testing options, our experienced plant scientists and crop specialists offer our clients with customized protocols to make sure the maximum output of each project.


  1. Elias, S. G., Copeland, L. O., Mcdonald, M. B., and Baalbaki, R. Z. (2012). Seed Testing: Principles and Practices. Michigan State University Press.