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

Abstract

Influence of experimental conditions on electrospray/ionization (ESI) mass spectra of ferrocene derivatives FcCHRAz (Fc = eta5-C5H5-Fe-eta5- C5H4; R = H, Az = benzimidazole; R = Ph, Az = 2-methylimidazole) has been investigated. The spectra of all the compounds revealed [M]+*, product 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 concentration, 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. It can give rise to wrong interpretation of the structure of investigated compound. At the same time, for 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 products yields on temperature and flow rate of mobile phase must be investigated.

The reactivity of ferrocenylalkyl azoles under the conditions of electrospray ionization

“…In this article, the results of the investigation of mechanisms of ionoformation of 1-ferrocenylmethyl-1H-pirazole FcCH 2 Pz (1), 2-methyl-1-(1-ferrocenylethyl)-1H-imidazole FcCH(Me)Im (2) Recently, we have discovered, that the shape of the ESI mass-spectra of ferrocenylalkyl azoles and ferrocenylalkanols essentially depends upon the conditions of the experiment (the analyte concentration, the solvent phase flow rate, solvent, temperature, electric potential) [1,10]. Thus in order to preserve the same ionization conditions the mass-spectra of an equimolar mixture of the compounds 1 and 2 was registered.…”

“…Other ions do not comprise deuterium. Using the mixture ACN/D 2 O (1:1 w/w) as a solvent but in the absence of D 2 O vapors (experiment 6) also brings to the enrichment of protonated molecules by deuterium [M 1 Two alternative explanations of these results can be suggested: (1) the protonation occurs in solution, and the isotope change of hydrogen takes place in the ions [M 1 +H] + in the gas phase; (2) protonation takes place mainly in the gas phase.…”

“…3) (Table 6) show that, these values, as expected, are in an antibate dependence (Eqs. (1) and (2)), i.e. the lower the reaction heat is, the higher the yield of the corresponding ion is.…”

“…It has been shown recently by us [1,2] that under the conditions of ionization electrospray (ESI) ferrocenylalkyl azoles FcCH(R)X (Fc -g 5 -C 5 H 5 Fe-g 5 [3] giving rise to bisferrocenylalkyl azole cations [(FcCHR) 2 Az] + ([MA] + ) also takes place (Fig. 1).…”

Reduction of matrix effects and improvement of sensitivity during determination of two chloridazon degradation products in aqueous matrices by using UPLC-ESI-MS/MS

“…An increase in intensity was still observed, however less significant than with the ammonia solution (data not shown). This behaviour could be attributed to the fact that electrospray ionisation is also strongly influenced by the flow rate and therefore by the spray geometry during postcolumn infusion of modifier [26]. Finally, the greatest intensity was obtained at a concentration of 10 mmol/L in the ammonia solution at an injection flow of 25 μL/min into the mobile phase (0.7 mmol/L ammonia totally in the mobile phase).…”