About pycnometric density measurements.

Pycnometric density is at the moment the closest approximation of true density calculated from the molecular weight and crystalline lattice of the product. It is determined by using helium pycnometers that offer the advantage of being easy-to-use and rapid, especially fully automated apparatus. If the accuracy and the reproducibility of the technique are sufficient to reveal minute variations, this data is of interest for characterisation of crystalline structures (polymorphs, pseudopolymorphs, amorphous state), detection of defects, pores or impurities, and possible changes in crystal density during compaction. The aim of this article is to investigate on the confidence that can be expected when measuring density with an AccuPyc 1330 pycnometer. The experiments carried out on glass beads, quartz and mannitol have shown that operating parameters can affect the accuracy of pycnometric density to the nearest 0.01 g cm(-3). If measurements are performed in optimal conditions, 0.02% accuracy can be obtained, otherwise it can fail to 0.1% or less, depending on the material and the variations in the standard volume.