Moisture content in a wide variety of products is an essential indicator of product quality – so essential that in many cases moisture content is regulated by government authorities. Google “moisture content regulations” and see for yourself. A useful if not essential tool to comply with these regulations is a moisture analyzer or moisture balance.
Elegant in design and simple in principle, a moisture analyzer replaces cumbersome drying ovens with a halogen heater mounted on a precision scale. The difference in sample weight before and after drying determines the moisture content of what is being tested. But while the principle is simple, correctly operating a moisture balance requires careful sample preparation and programming consistent with the product being analyzed.
A good example of a moisture analyzer is Kern’s MRS 120-3 model available from Tovatech. It uses the thermogravimetric process to determine moisture content with readability of 0.001 gram or 0.01 percent moisture content.
In this process ‘moisture’ includes all substances that volatilize during heating. This means moisture content is not restricted to water, but can also include, as examples, fats, oils, alcohols and solvents.
Sample Preparation to Determine Moisture Levels
Because different materials react differently to a moisture analyzer, sample preparation is important. For example, to prevent samples from exchanging moisture from the immediate environment they should be prepared just before analysis. Otherwise pack them in air-tight containers.
Distribute samples evenly and thinly on the moisture balance weighing pan to assure homogeneous heating and avoid encrustations that may develop in upper layers of the samples, thereby lowering evaporation rates. Coarse samples should be made finer by using a mortar or grinder – taking care not to heat them during this process. Light-colored samples react differently than dark samples in absorbing heat.
When determining moisture content of liquids, pastes or slurries spread the sample on a fiberglass filter or sandwich the sample between two filters to help assure even distribution, prevent the formation of drops and to increase surface area to speed evaporation. The fiberglass filters also prevent splashing or splattering of samples.
Accompanying instruction manuals detail steps to program moisture balances such as the Kern MRS 120-3 in accordance with samples being analyzed. Also included are tables of representative materials being analyzed, the sample weight, drying temperature and drying time.
How does your organization measure moisture content? What steps are outlined in the company operations manual concerning record-keeping?