11
Sample Analysis
Proper sample preparation and testing are critical to obtaining accuracy and
precision. Each sample has a specific characteristic composition; therefore, each
sample may require an individual method of analysis. However, guidelines can be
established for analysis of general sample types.
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Sampling – A representative sample is critical to obtain proper analysis.
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Preparation – As with any chemical analysis, a homogeneous sample is
critical to obtaining precision and accuracy.
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Weight – A consistent sample size helps ensure precision and accuracy.
Most CEM applications specify a sample size of 2-5 grams, emphasizing
the importance of a homogeneous sample.
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Holders – Absorbent pads to which a sample can be applied are used for
most analyses. Glass fiber pads are recommended because glass fibers do
not absorb microwaves. Other holders include Teflon coated glass fiber
mesh, a drying basket and a thermapad.
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Application – Most samples should be spread smoothly, avoiding lumps,
peaks or any uneven areas. Sample spread must be consistent.
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Drying Time – The drying time is determined by the type of sample and its
microwave absorbency. Constant weight drying permits drying of a sample
until a constant weight is achieved. Set time drying permits the control of
the sample analysis by entering a specified time and power level.
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Infrared Temperature – The infrared temperature measurement may be
used to operate at temperatures used in standard or vacuum oven
procedures.
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Microwave Power – The power necessary to dry a sample is determined by
sample composition. A sample should be tested at the highest possible
power without burning or degradation of the sample.
Sampling
Proper sampling of a product or process is critical in achieving proper moisture/
solids analysis. A representative sample is required to ensure that the test results
are representative of the entire batch or lot of material.
Many standard procedures such as AOAC, USDA and ASTM methods reference
sampling techniques. It is extremely important to follow techniques outlined in
these procedures for a particular sample type.
Proper handling and storage of the sample prior to analysis is also critical in
achieving accurate and representative results. Samples should not be exposed to
the air for long intervals prior to analysis. Proper storage also ensures that no
moisture is lost.