Protocol for determination of seed moisture content

Monday, November 10, 2003

Description
Protocol for determination of seed moisture content

Procedure
General Considerations

1. The total weight of seeds used for a moisture content determination should be sufficient to make the test accurate and yet not be wasteful of seeds. The sample should be fully representative of the accession and a minimum of 100 mg should be used to prepare the samples for the test. Accurate results were obtained using approximately 200 mg of seeds.

2. The lower the weight of seed used, the more accuracy is required to achieve a true result. Small samples should be weighed with an analytical balance to four decimal places using light-weight dishes (small aluminum dishes or petri dishes), so that the ratio of the weight of the seeds and the dish is not too disproportionate.

3. It is suggested that a minimum of three replicates of 100 mg of seeds or two replicates of 200 mg of seeds per sample be used for the moisture content determination.

4. Always work with care and finish one sample at a time. Do not leave the dishes open in the laboratory between weighings because the seeds will either lose or absorb water from the air and small changes in weights can result in large differences in the calculations when the amount of seed used is small.

5. High temperatures cannot be used to determine the moisture content because the oil will also vaporize and give a false result of water plus oil content. Temperatures of just over 100C allow evaporation of water and minimal vaporization of oils.

Equipment

Heat resistant dishes with cover, analytical balance, forced draft oven, desiccator with silica gel, tongs and oven cloth

Method

1. Weigh one clean numbered dish and cover accurately to 4 decimal places using an analytical balance. Write the weight (W1) in the notebook.

2. Add approximately 100 or 200 mg of seeds distributed evenly over the base of the dish, replace the cover and accurately weigh the dish and cover. Write this weight (W2) in the notebook.

3. Place the dish in a safe place and continue to do the second and/or third replicates in the same way.

4. When all samples have been weighed into numbered dishes, place each dish on top of its numbered lid in the oven at 100-105 C.

5. Wait for the oven to reach this temperature and heat the samples for 15-17 hours.

6. Remove the dishes from the oven, replace their covers and place in a desiccator to cool for 30 to 45 minutes at room temperature. After heating, make sure that the dishes are put directly into the desiccator so that the dry seeds do not absorb more moisture.

7. Remove the dishes one by one from the desiccator and immediately weigh each dish and cover, and write the weight (W3) in the notebook. Do not leave the desiccator open during the weighings.

8. Moisture content is calculated as the loss in weight as a percentage of the original weight of seeds. This is known as wet basis or fresh-weight basis, and is expressed to one decimal place. Algebraically, if W1 is the weight of the dish, W2 the weight of dish and seed before drying, and W3 the weight of dish and seed after drying, then:

% Moisture Content = 100 x ( W2 - W3 ) / ( W2 - W1 )

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Protocol for determination of seed moisture content