On-line supercritical fluid extraction and chromatography of organotins with packed microbore columns and formic acid modified carbon dioxide

Abstract

Supercritical fluid chromatography (SFC) using formic acid modified carbon dioxide and polymer encapsulated silica based stationary phases is suitable for the analysis with flame ionization detection of organotin compounds of general structure RnSnX4−n where n=4, 3 or 2. For ionic organotin compounds the retention time is independent of the identity of the anion, probably due to the formation of formate salts at the time of injection. A solventless injector is shown to be useful for injecting solvent volumes in the range of 0.5–50 μl, with solvent elimination prior to transferring the sample in the mobile phase to the column and as a simple in-line collection interface for SFC with supercritical fluid extraction (SFE). Various organotin compounds in a marine paint and spiked into a potato or almond matrix were determined on line, by SFE/SFC with flame ionization detection, with a limit of determination of about 1 ppm. The detection limit for typical organotin compounds using the flame ionization detector is about 0.5 ng in the chromatographic system described. SFC using formic acid modified carbon dioxide and flame ionization detection represents a considerable advance in the chromatographic analysis of ionic organotin compounds which are often time consuming and problematic to analyze by other methods.