Packed-column supercritical fluid chromatography/mass spectrometry via a two-stage momentum separator

The practical utility of a two-stage momentum separator for combining packed-column supercritical fluid chromatography (SFC) with mass spectrometry (MS) is described. A Hewlett-Packard model 1084B liquid chromatograph modified for packed-column SFC is connected to a linear fused-silica capillary restrictor housed in a heated probe held at 60 degrees at the terminus. A makeup of coaxial helium gas (1.5 L/min) or dissolved solvent (0.2-0.4 mL/min) can be introduced at the point of supercritical fluid expansion. The latter SFC effluent (0.3-2.0 mL/min) is expanded into a heated (44 degrees) desolvation chamber and directed through a nozzle positioned at the entrance of a two-stage momentum separator. Enrichment of the analyte relative to the volatile gases allows the transfer of sample particles to the MS ion source to produce electron ionization of flash-volatilized eluates. On-line SFC/MS separation and detection of low microgram levels of involatile, thermally labile analytes in synthetic mixtures is accomplished. Identification of an unknown compound in a drug tampering incident and the identification of an unknown metabolite isolated from horse urine is also accomplished.