Microwave Oven Technique
The microwave drying technique utilizes microwave energy to evaporate the water from the sample.
The LabWave
9000TM microwave moisture analyzer is a microwave oven developed
by the CEM Corporation (Matthews, NC) for "rapid" measurement of moisture
in materials such as food products. An internal balance is tared while
it is supporting two disposable glass fiber pads. The sample is spread
evenly between the pads and then heated at a certain intensity for a specified
time. The analytical balance periodically measures the sample weight allowing
the user to plot the slope of the drying curve. The test is terminated
after the sample has been heated for a specific time or when the slope
of the heating curve determined from two consecutive points falls below
a specified level (typically 0.2 mg of weight loss over a period of 10
seconds is considered satisfactory).
A table of LabWave 9000TM
drying times for several products can be found on the next page.
The LabWave 9000TM is capable of measuring the moisture or total solids of liquids, slurries, and solids containing between 0.01% to 99.99% moisture. According to the manufacturer, it has a resolution of 0.01%.
The inherent difficulty with microwave technology is that the microwave energy focuses on the center of the oven. Unless the sample is centrally located and evenly distributed, some portions may burn (oxidation) while other portions may be underprocessed.
