E-M-AwTherm-V1.1
Rotronic AG
Bassersdorf, Switzerland
Document code
Unit
AwTherm: Water Activity at Controlled Temperature
Instruction Manual for Software
Version 1.1
Document Type
Page
21
Document title
4
Sample preparation
4.1
Protection from environment
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 vapour may condense on the sample, and
render any measurement invalid.
4.2
Sample size and temperature equilibration time
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.
4.3
Best Practices
4.3.1
Precondition samples to measurement temperature
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.
4.3.2
Avoid condensation
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
© 2012; Rotronic AG
E-M-AwTherm v1.1
