Sample purification for spectroscopic high-pressure investigations by dynamic supercritical fluid extraction

A method for the high resolution purification of 1,4-bis-(n-alkylamino)-9,1 0-anthraquinone dyestuff samples based on a modified supercritical fluid ch romatography (SFC) equipment was developed to minimize errors in high-press ure solubility measurements. Impurities and by-products were eluted in a co ntinuous CO2 flow, the purification process could be observed by a diode ar ray spectrophotometer. The fact that both static and dynamic solubility exp eriments of a selected dyestuff gave consistent results turned out to be a credit point for this new method, which can be universally used for other p urifications, too. Besides, the necessity of calibrating directly in the so lvent gas is demonstrated, since some organic solvents lead to characterist ic spectral effects which can strongly disagree with those in CO2. Our expe riments showed a weakening of these effects towards longer alkyl chains of this substance class. In a separate section, some remarks are given concern ing the use of wavenumbers instead of wavelengths in such experiments. (C) 1999 Elsevier Science B.V. All rights reserved.