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Fundamentally any sample will try to come into equilibrium with its environment, so it is vitally important to keep samples as protected from the ambient environment as possible – to avoid its water activity changing before loading into the instrument. This is best achieved by placing the sample in a Rotronic PS14 or PS40 sample cup with a lid in place until the sample is ready to be placed in the instrument and its lid closed.
This is particularly important if the sample is chilled as vapor may condense on the sample, and render any measurement invalid.
Adequate time should be allowed for the sample to reach temperature in order to make a valid measurement. The time taken depends on the size, weight, and specific heat capacity of the sample. Difficulties in knowing the sample has reached the required temperature throughout are mitigated by consistency in procedures and practices as described in the following sections.
If the samples being tested are part of a process, if at all possible, make measurements at the temperature that the sample comes out of the process, and minimize the time taken to load the sample into the AwTherm.
If your sample is chilled below ambient or you need to make measurements at low temperatures, there is a risk of condensation forming. Condensation can form on chilled samples or on the inside of the AwTherm when the lid is open. As a guide in normal laboratory conditions, condensation can form on surfaces that are <15°C. It may be necessary to place the AwTherm in a cooler (drier) environment to prevent this occurring
Water activity is a qualitative measurement of product consistency, and so to record useful data, it is vitally important to make measurements in a consistent way. Define procedures: dwell times, tolerances, etc, and be consistent with their implementation.