Selecting the optimal sample size when characterizing a material using rapid loss-on-drying technology can be difficult to do.
Each material has unique characteristics that may influence how it should be tested.
Total Volatile Content – How much material is going to come off during a test? Is it 20%? Is it 2%? Is it 200ppm? The answer to this question will greatly influence the amount of material needed for an accurate test with an acceptable test time. For materials that expect losses greater than 20% only a few grams of material are needed. 5.0g ± 0.5g is a good initial testing sample size for materials with higher volatility. Once the initial analyses is finished the mass can be adjusted up or down to increase repeatability or reduce testing time, which is dependent on what condition is more desired by the user.
For materials that have a small amount of volatile content a larger sample size is needed. For materials with losses between 1 and 20% a good initial sample size is 10.0g ± 1.0g, and for materials with an expected loss less than 1% a samples size of 20.0g ± 2.0g is recommended. From these sizes the sample size can be adjusted for optimum instrument performance.
Sample Layering – Another factor to consider when selecting a sample size is sample layering. If the initial sample size selected is too large it could lead to sample material piling up. This causes the sample near the pan to be insulated from the heat source, which would cause a lower than expected result. Often times technicians attempt to compensate for this by increasing the temperature, which often leads to burning the top layer of sample material (similar to scorching the outer layer of food in an oven that is set too hot). If this is the case, try returning the testing conditions to a lower temperature and reducing the sample size while increasing surface area.
Flammability – When working with materials that can ignite, the amount of sample is a critical parameter of testing. Too much material could damage the instrument if it ignites, but too little material can hinder good repeatability from test to test. For samples that fall into this category it is best to start with 1.0g ± 0.2g of material, and increase the sample size in 0.5g increments until good testing conditions are achieved.
There are certainly other criteria that can influence the amount of sample needed, and each material will provide its own challenges for determining the optimal sample size.