Packed-column supercritical fluid chromatography—mass spectrometry and supercritical fluid chromatography—tandem mass spectrometry with ionization at atmospheric pressure

The combination of packed-column supercritical fluid chromatography (SFC) with atmospheric pressure ionization mass spectrometry (SFC—API-MS) is reported. This approach is novel in that the adiabatic expansion of total SFC effluent is subjected to atmospheric pressure chemical ionization (APCI) via a corona discharge with the aid of a heated region around the restrictor. The latter is a laser-drilled stainless-steel pinhole diaphragm which is commercially available, rugged, and easily handled. Supercritical carbon dioxide was modified with methanol to produce protonated molecular ions via APCI of representative steroids in synthetic mixtures and biological extracts. The separation time for these compounds was within a few minutes so that rapid analyses are possible. The single MS spectra readily indicate the molecular weights of these compounds although little structural information is provided. In those instances where structural information is desired the technique of tandem mass spectrometry (MS—MS) may be utilized. Thus SFC—MS—MS characterization of trenbolone produced a collision-induced dissociation product ion mass spectrum containing numerous structurally useful fragment ions. SFC—MS—MS analysis of a complex tissue extract fortified with low ppb levels of the same growth-promoting steroid and an internal standard readily revealed the target compound by this technique. It is suggested that SFC—API-MS is a practical approach to routine SFC—MS. The APCI technique reliability and good sensitivity for many classes of compounds while the pinhole diaphragm restrictor is much more rugged and easier to work with than those associated with capillar columns.