Sartorius MA35, Руководство по эксплуатации

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14
Basic Principles
Purpose
The moisture analyzer can be used for
quick and reliable determination of the
moisture content of materials of liquid,
pasty, and solid substances using the
thermogravimetric method .
Material
The moisture of a material is often
mistakenly equated to its water content .
In fact, the moisture of a material
includes all of the volatile components
which are emitted when the sample is
heated, irrespective of the type of
material . Among such volatile
substances are:
– Water
– Fats
– Oils
– Alcohols
– Organic solvents
– Flavorings
– Volatile components, products of decom-
position (when a sample is overheated)
There are many methods for determining
the moisture content of a substance .
Basically, these methods can be divided
into two categories:
When absolute methods are used, the
moisture content is directly determined
(for example, as a weight loss registered
during the drying routine) . These
methods include oven drying, infrared
drying, and microwave drying . All three
of these methods are thermogravimetric .
When deductive methods are used, the
moisture content is indirectly deter-
mined . A physical property related to the
moisture in the substance is measured
(e .g ., conductivity) . These methods
include capacitive and spectroscopic
approaches .
Thermogravimetry is the process of
determining the loss of mass that occurs
when a substance is heated . In this pro-
cess, the sample is weighed before and
after being heated, and the difference
between the two weights is calculated .
In a conventional drying oven, circulat-
ing hot air warms the sample from the
outside to the inside . Efficiency is lost
during drying because as the moisture
evaporates, it cools the sample surface .
By contrast, infrared rays (IR rays) pene-
trate the substance . The majority of the
rays reach the interior of a sample, and
then directly heat the sample .