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The drying oven method is a thermogravimetric method (loss on drying) in which the sample is dried for a defined period of time at constant temperature. The moisture content is determined by weighing the sample before and after drying and determining the difference.
In the drying oven, samples are heated by convection. This means the samples are at the same temperature as the drying oven. When using a moisture analyzer, the sample heats up and dries by absorbing infrared radiation from the heating element. The sample's temperature and drying time depends on its absorption characteristics.
This is a common misconception. Everything which evaporates upon heating is named moisture. Water may be a part of this but there may be other substances which also evaporate, such as alcohol or solvents.
In general, all kinds of samples are suitable for both the drying oven and the halogen moisture analyzer. Which method is best for you, depends on how fast you need the result or if you need the result using an official method. Sometimes, for example, in goods-in or final product quality control, moisture analyzers are used in parallel with a drying oven. Fast analysis with the moisture analyzer is done to optimize processes and the drying oven is used for official documentation purposes.
Many industry regulations require manufacturers to follow a standard method. However, it is acceptable to use a moisture analyzer if you can prove its results are the same as those from the drying oven procedure and are of the same level of accuracy. This requires developing a drying method for the moisture analyzer and cross-validating it against the drying oven through a series of analyses. METTLER TOLEDO's application database contains over 100 free ready-to-use cross-validated drying methods. Contact us if you don't find what you need.
You can do this either through the ID management functionality on our moisture analyzers or in the differential weighing application on our balances. If your batch number is a barcode, you can even connect a barcode reader to scan it, or any other ID.
Manual processes are more prone to error so it's best to use the built-in balance application or a software solution (LabX) with a balance to capture all the results and do the calculations automatically. It's not only much faster but it's error-free too. Results can be printed out for your lab journal or saved on a USB stick to be saved electronically. LabX saves everything in a secure database so you can be sure your data is safe. The LabX report generator enables you to create elegant reports with charts which can be printed out or saved electronically.
Good labelling is key. Using barcode labels uniquely identifies each sample. A barcode reader attached to the balance ensures that no mix-ups occur and weighing results are correctly logged against each sample. Use of a barcode reader is fully supported by the differential weighing application on the balance and by LabX.
Moisture content is the amount of moisture in the sample given as a percentage of the sample's original (wet) weight. Dry content is the amount of solids which are left after drying given as a percentage of the sample's original (wet) weight. ATRO moisture (AM) is the amount of moisture in the sample given as a percentage of the sample's final (dry) weight. Different industries use different units e.g. in wood or pulp, ATRO is commonly used.
The loss on drying procedure can be used to determine moisture content (MC) or, alternatively, dry content (DC). A sample may undergo extensive drying to remove all the moisture. The dry content remaining may be termed the total solids (TS).
Dry content and total solids mean the same thing. They describe the amount of material remaining after all the moisture has been evaporated.
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