Purged Splitless Injection in Microcolumn Supercritical Fluid Chromatography

1991

Abstract. Solute focusing is an important topic in chromatography, but it has not been discussed extensively in the recent supercritical fluid chromatography literature. The purpose of this paper is to review the different methods that have been used to focus solutes in supercritical fluid chromatography. The theoretical basis for phase ratio and partition coefficient focusing is described. Different solute focusing devices that are used in on-line supercritical fluid extraction and chromatography are shown. The methods and principles of removing the solvent from the solutes prior to the analytical column, and hence reducing band broadening in the column due to the solvent, are discussed in context with the use of a retention gap or a mixing chamber, and in solvent vent injection.

Section: Solvent Ventmentioning

confidence: 76%

“…Hirata et al [13,14] described a splitless injection method where up to one microliter of sample was injected. The principle of the mixing chamber injection method is to dilute the organic sample solvent so that the solvating power of the solvent is less than that of supercritical CO,.…”

Section: Mming Chambermentioning

confidence: 99%

Solute focusing in supercritical fluid chromatography

Koski

1991

“…The solutes are carried down the column with the solvent until the dissolving power of the solvent decreases due to the mixing of the solvent and the mobile phase. In SFC, the same phenomenon occurs during injection if the solvent is not readily soluble in the supercritical mobile phase [13,14]. In solvent vent injection in which the venting gas pushes the liquid solvent into the precolumn (similar to injections in gas chromatography), the precolumn is dynamically coated with the sample, while the solvent is evaporated into a flow of nitrogen gas.…”

Section: Resultsmentioning

confidence: 99%

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

Koski

Markides

1991

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.

“…Hirata et aE. [5] recently showed that the most significant factor leading to peak splitting in direct injection is the concentration of sample solvent in the mobile phase. As a result, they have developed a purged splitless injector that allows mixing before the solvent and solutes enter the column.…”

Section: Injection Solvent Considerations the Injectionmentioning

confidence: 99%

Optimization of internal valve injection in open tubular column supercritical fluid chromatography

Tuominen

Markides

1991

Abstract. As in the case of all chromatographic methods, the ideal sample introduction method for supercritical fluid chromatography (SFC) would provide a narrow and sharp solvent peak (or no solvent peak), quantitative transfer of the sample into the column, and high reproducibility. Elimination of the solvent before the solutes enter the column would be preferred; however, this practice is always associated with the risk of partial solute elimination. In open tubular column SFC, samples are normally introduced using a smallvolume internal loop valve. These valves can be operated such that none, some, or all of the solvent is eliminated. Several approaches were quantitatively evaluated, and optimized conditions were determined. Particular attention was given to trace analysis. The minimum detectable levels (S/N >4) achievable using a flame ionization detector were determined to be approximately 30 ng (150 ppm) for split injection, 4 ng (20 ppm) for delayed split injection, and 1 ng (5 ppm) for direct injection.