Supercritical fluid chromatography/chemical ionization/mass spectrometry of some anticancer drugs in a thermospray ion source

Abstract

A packed‐column supercritical‐fluid chromatograph was interfaced with a mass spectrometer via a modification of a thermospray probe. This modification allowed a capillary restrictor for the supercritical fluid (CO₂) and reagent gas for chemical ionization to be introduced directly into a thermospray source. Chemical ionization conditions were observed when either the filament or discharge electrode was used and the source pressure was above 0.5 torr. The discharge electrode produced more efficient ionization, resulting in approximately a tenfold larger signal than that observed in the filament mode. The usefulness of this instrumentation was demonstrated on several anticancer drugs. Methanol positive ion chemical ionization (PICI) spectra were recorded for cyclophosphamide, diaziquone, mitomycin C and thiotepa. Methane PICI spectra of thiotepa were obtained in the absence of methanol as a mobile‐phase modifier. A 50 ng on‐column injection of diaziquone produced approximately a 6:1 signal to noise ratio in the scanning mode.