INTERFACE FOR OPEN-TUBULAR COLUMN SUPERCRITICAL-FLUID CHROMATOGRAPHY ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION MASS-SPECTROMETRY

A new interface for open tubular column supercritical fluid chromatography (SFC) to atmospheric pressure chemical ionization mass spectrometry (APCI-MS) is described. The interface was designed to permit transport of the supercritical mobile phase into the ionization region of the mass spectrometer while maintaining its temperature to within +/- 1-degrees-C of the chromatographic oven temperature. Temperature control of the interface-transfer line was achieved using preheated gas streams from the chromatographic oven and an active electrical insulation. Ionization was achieved by a point-to-plane corona discharge. The performance of the SFC/MS interface is demonstrated using a number of selected analytes showing preserved chromatographic resolution, inertness in the transfer line, and independence of mobile-phase flow rate on ionization, as well as characterization of ionization and fragmentation patterns for compounds from different chemical classes. Test analytes included a polarity mixture over the solubility range of carbon dioxide. Minimum detectable quantities for anthracene and trilaurin were about 1 ng (S/N = 3) and 10 pg, respectively, while selected ion monitoring was used. An average retention time reproducibility of 0.24 % RSD was displayed with an average 2.6 % RSD in relative peak height. Retention time correlation between chromatograms obtained with flame ionization detection and mass spectrometric detection is also demonstrated.