Study of dead volume measurement in packed subcritical fluid chromatography with ODS columns and carbon dioxide-modifier mobile phases

Studies were done for providing a simple, rapid and reliable procedure of v oid volume measurement. in packed subcritical fluid chromatography (pSubFC) , with CO2-modifier mobile phases containing high modifier amounts. Methods used in RPLC with ODS columns were applied in pSubFC: gravimetric, homolog ous series linearisation and unretained marker injection. Results lead us t o propose the method of marker injection to determine the void volume in pS ubFC. Acetonitrile was chosen as the void volume marker among six tested ma rkers. Furthermore, void volume variations vs. the modifier volume (from 5 to 45%) were studied for nine organic modifiers. The void volume variations were related both to adsorption-desorption phenomena between the mobile ph ase and the stationary phase and to mobile phase density changes. These var iations allowed the classification of the modifiers into four groups on the basis of the molecular interactions. (C) 2000 Elsevier Science B.V. All ri ghts reserved.