Peer Reviewed: Unified Chromatography with CO2-Based Binary Mobile Phases

Abstract

C hromatographic methods are usually classified according to the physical state of the mobile phase-for example, GC, supercritical fluid chromatography (SFC), and LC. This admittedly oversimplified classification scheme exists partly because of the similarity of most chromatographic stationary phases, which are usually either polymers or solid adsorbents and are often deactivated by some chemically bonded moiety. Because of the banality of stationary phases, any attempt to unify the various forms of chromatography will naturally center on the mobile phase (1-4). To date, many researchers consider the most promising approach to unification to be the use of CO 2 as the mobile phase because of the "tunable" solvent strength of this fluid.

Supercritical fluid chromatography for the enantioseparation of pharmaceuticals

“…In practice modifier concentrations are kept below 50%. One reason is that using higher concentrations of modifier might alter the critical point of the mixture with carbon dioxide too much and a situation might occur in which the mobile phases no longer exists in a sub-or supercritical state but in a liquid-vapor state, that no longer displays the supercritical-fluid characteristics [73][74][75]. A second reason is that small concentrations of polar modifiers already can dramatically increase the solvent strength [35,73].…”

Synthesis of dimethyl carbonate in supercritical carbon dioxide

“…Data available for the conditions defined in our study (423 K, 60 < CO 2 < 76 mol%) point to a corresponding critical pressure of around 16 MPa (Wells et al, 2003). In order to discover to what extent the addition of tin compounds affects the system, the phase behavior of the three-component mixture was visually examined by conducting the reaction in a 30 cm 3 stainless steel autoclave equipped with sapphire windows (Top Industrie S.…”

Determination of thermodynamic properties by supercritical fluid chromatography

“…Experimental evidence has been accumulated of irreproducible retention times in SFC [126][127][128] and extraction efficiencies in SFE [129][130][131] suggesting that the entrained helium acts as a negative modifier (antisolvent). Other unexpected deleterious effects that might occur with HHPCO 2 were discussed by Parcher and Xiong [132] and by Wells et al [133]. Although thermodynamic implications of entrained helium may simply and fairly accurately be treated by a cubic EOS [134], the principal cause of the unexpected effects of HHPCO 2 is probably the lack of thermodynamic equilibrium in HHPCO 2 tanks [135].…”