I.Purity Test:

.     The physical purity analysis of a seed sample in the seed testing laboratory refers to the determination of the different components of the physical purity viz pure seed, other crop seeds, weed seeds and the inert matter.

The objective of the purity analysis is to determine whether the submitted seed sample(by inference the seed lot)conforms to the prescribed quality standards in regard to purity components.

The purity analysis is done on the working samples of prescribed weight drawn from submitted sample (please refer table2.1 in Hand book of seed testing)  The  analysis may be made on one working sample of the prescribed weight or on two sub-samples of at least half this weight, each independently drawn.

            The number of decimal places to which the working sample and the components of the working sample should be weighed is given below:

Weight of the working sample in gram

The number of decimal places to which the working sample and its components should be weighed

Example

Less than 1

4

0.7534

1 to 9.9999

3

7.534

10 to 99.99

2

75.34

100 to 999.9

1

753.4

1000 or more

0

7534

 

PURE SEED: The pure seed means the seeds of kind/species stated by the sender, or found to predominate in the test. It includes all botanical varieties and varieties of that kind/species.

OTHER CROP SEED: It relates to the kinds of crops other than the kind being examined.

WEED SEED: It includes seeds of those species normally recognised as weeds or specified under a regulation of the Seed Act as a noxious weed.

INERT MATTER: Inert matter includes seed units and all other matter and structures that are not defined as pure seed.            

MAKING THE PURITY SEPARATION:

Place the working sample (or sub sample) on the clean surface of a purity work board and do the following.

 

1.      Examine the sample to determine whether it conforms to the variety/species name under which it has been submitted.  The file samples (authentic samples of the same variety) maintained in the seed herbarium are of great value in making this decision.  In case of any doubt the sample  under examination may be compared with the file samples of the same variety/species.

2.      Examine the sample to determine whether it contains small inert matter which could be removed sieving.

3.      Examine the sample to determine whether it contains light weight material which may be removed by blowing.

 

If small inert matter is present which can be removed by  sieving or a preliminary blowing, use the appropriate sieve to separate it.  If the light weight material is present blow the sample until all the light weight material is removed from the heavy fraction.

Check or Duplicate Tests

Purity analyst must  be  familiar  with  the  seed standards.  Analysis results near the border  line in relation to prescribed seed standards may be confirmed by one or more further tests and the average may be reported.

However, if a duplicate analysis is made of two half-samples, or whole samples, the difference between the two must not exceed the permissible tolerance.

If the difference is in excess of the tolerance, employ the following procedure:

1.      Analyse further pairs (but not more than four pairs in all), until a pair is obtained which has its members within tolerance.

2.      Discard any pair in which the difference between its members exceeds, twice the tolerance.

 

Calculation of Results

The percentage by weight of each of the component parts should be calculated to one decimal place.

 

Reporting results

The result of a purity analysis shall be given to one decimal place and the percentage of all components must total 100.  Components of less than 0.05% shall be reported as ‘Trace’.

 

The percentage of pure seed, other crop seed, weed seed and inert matter must be reported in the spaces provided on the Analysis  Certificate.  If the result for a component is nil, this must be shown as ‘0.0’ in the appropriate space.