Effect of the addition of viscous matrices to the mobile phase on chromatographic performance in liquid chromatography-fast atom bombardment mass spectrometry

Abstract

The effect of the pre-column addition of a viscous matrix to the mobile phase in liquid chromatographic-fast atom bombardment mass spectrometric experiments was studied with respect to the chromatographic process. A series of experiments, designed to discriminate against the mass spectral components, were conducted with six compounds, ranging in mass from 100 to 1100 daltons and distributed into three chemical classes. Several chromatographic indicators such as retention times, capacity ratios, number of theoretical plates, peak widths, resolution and separation impedance were monitored as a function of the glycerol content of the mobile phase. The results obtained indicate that the retention times and the capacity ratios decrease with increasing glycerol content of the mobile phase. Increasing concentrations of glycerol also reduce the number of theoretical plates in the chromatographic system and generally have a detrimental effect on peak widths for glycerol contents above 5%. However, lower glycerol contents produce negative effects on compounds with smaller capacity ratios but not on compounds with higher capacity ratios such as peptides. Furthermore, the increase in glycerol concentrations reduces the chromatographic resolution for all classes of compounds studied and creates a significant increase in the separation impedance of the system, resulting in higher operation pressures. The overall effect of a viscous matrix in the chromatographic system can be rationalized in terms of the modification of the analyte distribution between phases and changes in the kinetics of the system created by an increase in mobile phase viscosity.