Letter: Influence of Experimental Conditions on Electrospray Ionization Mass Spectrometry of Ferrocenylalkylazoles

Abstract

The influence of experimental conditions on electrospray/ionization (ESI) mass spectra of ferrocene derivatives FcCH(R)Az (Fc=ñ5–C5H5–Fe–ñ5–C5H4; R=H, Az=benzimidazole; R=Ph, Az=2-methylimidazole) has been investigated. The spectra of all the compounds revealed [M]+·, products of its fragmentation [FcCHR]+ as well as products of ion/molecular interactions (protonated molecule [MH]+, binuclear ion [(FcCHR)2 Az]+, dimeric ion [M2]+· and its protonated form [M2H]+). Relative abundances of these ions appreciably (more than one order) depend on experimental conditions: analyte concentration, temperature of heated capillary, spray voltage, flow rate of mobile phase and polarity of solvents. Established correlations allow the selection of optimum experimental conditions for registration of ESI mass spectra, as required by the application. If an unknown compound is to be identified, it is necessary to operate by using polar solvents, small concentrations, low temperature of heated capillary, high spray voltage and flow rates. There are high-intensity binuclear and protonated dimeric ions in mass spectra under other conditions. These can give rise to the wrong interpretation of the structure of the investigated compound. At the same time, for the study of ion-molecular processes by ESI-MS, it is necessary to use concentrated samples in non-polar solvents. In this case, the dependence of reaction product yields on temperature and flow rate of the mobile phase must be investigated.