Preservation of column efficiency when using solvent vent injection in open tubular column supercritical fluid chromatography

Abstract

Abstract. The use of small internal diameter precolumns (11-25-pm i.d.) helped solute focussing when using solvent vent sample introduction in open tubular column supercritical fluid chromatography (SFC). Column efficiencies were similar to those obtained with split injection (3000-5000 plates m-l). Trace analysis in SFC was improved because large volumes (1 pL) could be introduced for analysis with little sacrifice in column efficiency.

Supercritical Fluid Chromatography and Extraction

“…Koski and Lee reviewed solute focusing techniques useful for injection in open-tubular SFC (128). Koski et al showed how the addition of a small-inner-diameter precolumn could improve solute focusing when using a solvent-vent injection technique (129). Koski et al described a solvent-venting injector using a short packed column as the solute focusing device, allowing injections up to 3 fiL onto 50-jun open-tubular analytical columns (130).…”

Solute focusing in supercritical fluid chromatography

“…A solvent that was not readily soluble in supercritical CO, has been used to dissolve the sample from the precolumn and focus it at the beginning of the analytical column [16]. Benzene (0.1-0.2 pL) was chosen for evaluation as a "chaser."…”

“…The length of the precolumn, and hence the possible sample plug length, is not the main reason for high efficiency [16]. A sample of n-alkanes (C,,,,) was analyzed with 25-pm i.d.…”

“…In SFC, there have been several different methods that have been used to focus the solutes. Focusing of nonvolatile compounds occurs (a) when the solvating power of the supercritical fluid suddenly decreases either by decreasing the pressure [l-71 or by increasing the temperature [8-121, (b) when a mixing chamber is used in front of the analytical column [13-151, (c) when samples are introduced with solvent vent injection [16,17], (d) when a small volume of solvent is introduced as a "chaser" to refocus the sample after solvent venting [16], and (e) when an uncoated precolumn (retention gap) is used in front of the analytical column [18].…”