Moisture Content, Water Content, Loss on Drying, Part 2: Special Possibilities Using the TGA

The presence of water in polymers, pharmaceutical substances or foodstuffs is often unwanted. The determination of the water content in different materials is therefore of great importance. Besides “water content”, the terms “moisture content” or “loss on drying” (LOD) are also often used. In Part 1 of this series, we defined what the terms mean and Introduction described some of the methods used to determine these quantities. In this second part, we want to discuss special possibilities using the TGA. In addition, we will discuss the relationship between LOD, sample weight and the accuracy of LOD in thermogravimetric measurements.

Introduction

In Part 1 of this series [1], we described two gravimetric techniques (TGA and the halogen moisture analyzer) and the Karl-Fischer titration for determining the water content in materials. In contrast to the Karl-Fischer titration, we saw that gravimetric methods are not selective because the mass losses measured during drying can be also be caused by the loss of other volatile substances or decomposition products and not only by the loss of water. Gravimetric methods are only selective with regard to water if the gaseous products released during the drying process are continuously identified. This is possible if the TGA is combined with a suitable evolved gas analysis system. If decomposition processes begin during drying, decomposition and drying can be differentiated by carrying out the drying process under reduced pressure. This can be done by operating the TGA at low pressure.

_{Moisture Content, Water Content, Loss on Drying, Part 2: Special Possibilities Using the TGA | Thermal Analysis Application No. UC 521 | Application published in METTLER TOLEDO Thermal Analysis UserCom 52}