Limits and effects of precolumn addition of thioglycerol in liquid chromatographic-fast atom bombardment mass spectrometric systems

Abstract

A series of experiments were conducted in order to determine the effect of the precolumn addition of a viscous matrix such as thioglycerol on the chromatographic performance of liquid chromatographic-fast atom bombardment mass spectrometric (LC-FAB-MS) systems. In those experiments, the concentration of thioglycerol in a mobile phase consisting of acetonitrile-water-trifluoroacetic acid was varied and important chromatographic parameters such as retention times, capacity factors, number of theoretical plates, peak widths, resolution and impedance of separation were monitored for analytes such as met-enkephalin, leu-enkephalin and p-hydroxybenzoic acid. The results obtained indicate that for concentrations of thioglycerol in the mobile phase below 3% most chromatographic indicators are only slightly affected. However, for concentrations of the viscous matrix above that value the capacity factors are significantly decreased, indicating that thioglycerol is behaving as an efficient organic moderator, and peak broadening becomes important, having a detrimental effect on the performance of the system. Van Deemter plots obtained for the analytes at concentrations of thioglycerol in the mobile phase of 0-15% reveal that the major effect of thioglycerol is to reduce the mass transfer efficiency in the chromatographic system at high velocities and concentrations of thioglycerol above 3%. Comparison of the effects of viscous matrices such as thioglycerol and glycerol on the chromatographic performance of LC-FAB-MS systems indicates that the chromatographic efficiency is almost independent of the matrix concentration when the systems are operated near their optimum linear velocities and that high matrix contents and high linear velocities can be used with little decrease in efficiency if the systems are operated at higher temperatures.