Comparison of Eluents in Supercritical Fluid Chromatography

Abstract

The chromatographic behavior of a number of low boiling eluents has been compared in supercritical fluid chromatography ( S F C ) with packed columns. Unmodified silica gel has been used as the stationary phase and a test mixture of polycyclic aromatic hydrocarbons ( P A H I S ) as the substrate. Carbon dioxide, nitrous oxide, trifluoromethane, chlorotrifluoromethane, n-pentane, n-butane, 1-butane, propane, ethane, dicthylether, and dimcthylethtr have beon investigated as mobile phases. LEYENDECKER ET ALOf the mobile phast -C O L , N 2 0 , C 2 t f 6 , C H F 3 , and C C I F J , which a l l possess low c'r? ticdl ternp(.ratur<s, comparisons were made at the bamc pressure and at similar reduced pressure. Poor transport properties were observed f o r C C l F 3 , exemplified by extremely high capacity ratios for the P A H ' s . Of the remaining tour mobile phases, at the same pressure, the highest capacity ratios were found for C L t I 6 , followed by C O L , N 0 a n d C I i F 3 . T h y highest 'esolution was obtained with C2H6, followed by C H F 3 , N 0 , and C 0 2 . A t 5iniilar reducca pressure, C2t16shched again thc3 hiyh2st capacity ratios, while CHF' C 0 7 , and N , O ndd lowtr values. I h e resolution sliowed a similar o r d e r . 2 2 3 ' 2For a given mobile phase, capacity ratio and resolution were correlated. 7'0 d first approximation, a hi<!hi%r capacity ratio leads to higher resolution. This correlation differs, however, f o r d fferent eluents. F o r instance, among all mobile phases the highest resolutions at a glven k ' were found f o r CHF3.

Temperature effects for chiral separations using various bulk fluids in near-critical mobile phases

“…This behavior is typical of near-critical mobile phases. 11,12 When carbon dioxide was replaced by HFC-134a, comparable behavior was observed (Fig. 2).…”

Comparison of eluents in supercritical fluid chromatography as based on density and free volume

“…On comparing retention between chemically similar mobile phases at the same temperature and pressure in SFC it is observed that the transport ability decreases with decreasing boiling temperature (and critical temperature) of the eluent. This has been reported for a comparison of alkanes from pentane to propane [2,3], and the still higher retention obtained with an ethane mobile phase [4] corresponds to this trend. Similarly, retention was higher with dimethyl ether than with diethyl ether [l].…”

Optimization of chiral resolution using packed columns with carbon dioxide-based mobile phases

“…This effect is well known and can mainly be attributed to the increased solvating ability of the mobile phase at higher density, although other factors are important. [16][17][18][19] This effect is not specific to the chiral recognition process since a similar effect is observed when the same analytes are chromatographed on a cyano bonded phase.…”