Source of band broadening in liquid chromatographic-fast atom bombardment mass spectrometric systems with precolumn addition of viscous matrix to the mobile phase

Abstract

The factors affecting band broadening in liquid chromatographic-fast atom bombardment mass spectrometric (LC-FAB-MS) systems using precolumn addition of glycerol to the mobile phase were investigated and their relative importance evaluated. The integrated LC-MS system is subject to three sources of band broadening, namely the chromatographic system, the interface and the mass spectrometer. The individual variances associated with these components can be used to estimate the total variance of the system. The factors affecting broadening in the chromatographic system were identified by examination of the Van Deemter plots obtained for several types of compounds at glycerol concentrations ranging from 0 to 20%. The plots reveal that the C term is significantly affected by an increase in glycerol concentration and that the main factor affecting broadening is a change in the diffusion coefficient, D m. The increase in the variance associated with the dead volume of the chromatographic system, as measured with a non-retained species, indicates that the increase in the viscosity of the mobile phase on addition of glycerol also results, to a lesser extent, in band broadening as a consequence of the change in flow dynamics within the system. Investigation of the factors affecting band broadening in the interface show that the main source of broadening is the wetting of the probe tip, which is far more important than the dead volume introduced by the transfer capillary. The band broadening induced by the mass spectrometer in the LC-FAB-MS system is essentially related to the scanning speed used for the analysis.