Interactions supercritical fluid chromatography

Young and Weber [397] presented an equilibrium and rate study of analyte-matrix interactions in SFE in aqueous matrices, while correlation of SFE with supercritical fluid chromatography (SFC) in aqueous media has been reported by Yu et al. [398]. Tena et al. [399] screened PAHs in soil by on-line fiber-optic-interfaced SFE spectrometry. 

Mobile fluid interaction with the stationary phase in SFC was investigated with mass spectrometric tracer pulse chromatography (96). Using capillary supercritical fluid chromatography, the effect of methanol as an additive was studied on the partition behavior of n-pentane into 5 % phenylmethylsilicone stationary phase. The results showed that the mobile fluid uptake by the stationary phase decreased with increasing temperature and pressure. Thus suggests that stationary phase swelling, may occur in SFC. 

The effect of temperature, pressure and density on solute retention (k1) in supercritical fluid chromatography (SFC) has been well studied.(1-6) Retention in SFC depends upon both solute solubility in the fluid and solute interaction with the stationary phase. The functional relationship between retention and pressure at constant temperature has been described by Van Wasen and Schneider. ( 1 ) The trend in retention is seen to depend on the partial molar volume of... 

Retention and selectivity in supercritical fluid chromatography (SFC) are a complex function of many experimental variables and are not as easily rationalized as in the case of gas and liquid chromatography. Retention in SFC is dependent on temperature, density (and pressure drop), stationary-phase composition, and the mobile-phase composition. Many of these variables are interactive and do not change in a simple or easily predicted manner [1]. 

Condo PD, Sumpter SR, Lee ML, Johnston KP. Partition coefficients and pol5uner-solute interaction parameters by inverse supercritical fluid chromatography. Ind Eng Chem Res 1996 35 1115-1123. 

CE = capillary electrophoresis, SFC = supercritical fluid chromatography, HILIC = hydrophilic interaction chromatography. 

Porous graphitic carbon (section 4.2.5) is an inert but highly retentive sorbent under supercritical fluid chromatography conditions. Supercritical carbon dioxide is a weak eluent for porous graphitic carbon and even compounds such as naphthalene are difficult to elute in a reasonable time [72]. Low molecular mass polar compounds generally have poor peak shapes, but in this case most likely due to limited solubility in tbe mobile phase rather than undesirable interactions with active sites on the stationary phase. The flat surface of porous graphitic carbon leads to preferential adsorption of... 

Condo, P.D., Sumpter, S.R., Lee, M.L. and Johnston, K.P. (1996) Partition Coefficients and Polymer-Solute Interaction Parameters by Inverse Supercritical Fluid Chromatography, Ind. Eng. Chem. Res. 35, 1115-1123. 

If the analyte is soluble in a SF yet cannot be extracted from the matrix, the analyte matrix interactions may be too strong. The problem may be overcome by the addition of modifiers to the supercritical fluid, or by the direct addition of a modifier to the extraction vessel. Several papers dealing with the use of modifiers for supercritical-fluid chromatography (SFC) (89-91) and SFE have been published (92-94). Modifiers have two basic effects on the SFE of analytes from a matrix. They can interact with the surface of the matrix displacing the analyte into the SF. To distinguish between the two types of modifiers, they are commonly termed solvent modifiers and matrix modifiers, respectively. 

JD Wechwerth, PW Carr. Study of interactions in supercritical fluids and supercritical fluid chromatography by solvatochromic linear solvation energy relationships. Anal Chem 70 1404, 1998. 

The mobile phase is the phase which moves in a definite direction. It may be a liquid (LC and CEC), a gas (GC), or a supercritical fluid (supercritical-fluid chromatography, SFC). The mobile phase consists of the sample being separated/analyzed and the solvent that moves the sample through the column. In the case of HPLC the mobile phase consists of a non-polar solvent(s) such as hexane in normal phase or polar solvents in reverse phase chromotagraphy and the sample being separated. The mobile phase moves through the chromatography column (the stationary phase) where the sample interacts with the stationary phase and is separated. 

Weckwerth, J.D. Carr, P.W. (1998).Study of Interactions in Supercritical Fluids and Supercritical Fluid Chromatography by Solvatochromic Linear Solvation Energy Relationships. Anal. Chem., 7, 70,1404-1410. 

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