Universal electromagnetic suspension balance with nanogramme mass resolution for measurement of sorption on small samples in top and bottom loading configurations

Abstract

Determination of mass increase or decrease of very small amplitude is a task which goes hand in hand with gravimetric adsorption and absorption measurement and thermogravimetry. Samples are subjected to various process conditions and as such can experience a change in mass, i.e. when adsorbing gas from the process atmosphere, or can decrease in mass, such as when being dried or when thermal decomposition takes place. Current instruments used for such analysis, especially at high pressures, are often based on magnetic suspension balances, and have a maximum mass resolution of a few 10−6 g. This necessitates more often than not quite significant sample quantities, which can sometimes not easily be manufactured, e.g. in the case of metal organic framework adsorbents, or which in other cases do not have a sufficient specific surface area resulting in low measuring effect. A new apparatus based on a high resolution thermogravimetric analyser has been developed. This new apparatus combines very high resolution of up to a few 10−8 g with a relatively high sample mass of up to 1.5 g, whilst eliminating many of the disadvantages of the microbalances previously used in magnetic suspension balances. An interface was developed which permits free configuration of the new balance as top or bottom loading. Validation measurements of known adsorbents were subsequently performed, with sample quantities up to a factor of 174 smaller than in literature.