A Predictive Model for Matrix and Analyte Effects in Electrospray Ionization of Singly-Charged Ionic Analytes

Abstract

In electrospray ionization (ESI), droplets with a surface excess charge are created. The rate of production of surface excess charge is a constant and is equal to the rate of ion production. The ions appearing in the mass spectrum are postulated to be those that formed the surface excess charge at the time of droplet formation (or their collision products). An equilibrium model based on competition among the ions in the solution for the limited number of excess charge sites has been developed. This model accurately predicts the response curves of singly-charged ionic analytes as a function of the concentration of electrolyte and other analytes and provides an explanation for the selective effectiveness of ESI. At low concentrations of total analyte (micromolar and less), the response curves are linear, indifferent to the presence of other low concentration analytes, and suppressed by electrolyte concentrations in excess of the minimum required. At higher analyte concentrations, the response becomes independent of analyte concentration but highly affected by the presence of other analytes.

1,2-Dimethylimidazole-4-sulfonyl chloride, a novel derivatization reagent for the analysis of phenolic compounds by liquid chromatography electrospray tandem mass spectrometry: Application to 1-hydroxypyrene in human urine

“…Firstly, compared with the calculated pK a of 3.3 for the acid form of the dansyl group [16], the pK a of dimethylimidazole acid form is 8.0 [25]. Thus, at many values of pH typically used in LC-ESI-MS/MS analyses, a DMIS derivative will show a higher degree of ionization than will the comparable dansyl derivative, and thus higher ionization efficiency in ESI [26], possibly leading to lower detection limits. A second advantage of derivatization with DMISC was observed in the MS/MS spectra of OHPAH derivatives.…”

Relative importance of basicity in the gas phase and in solution for determining selectivity in electrospray ionization mass spectrometry

“…The relationship between surface activity and response was observed as early as 1983 in the investigations of Iribarne et al of atmospheric pressure ion evaporation mass spectrometry [20]. Increased response for surface active analytes was predicted by Enke's equilibrium partitioning model based on the enhanced ability of such analytes to compete for the surface excess charge phase in electrospray droplets [21]. Indeed, the Enke group observed electrospray response to correlate linearly with the nonpolar surface area of small peptides, which was taken as a measure of surface activity [22].…”

A simple model for the disintegration of highly charged solvent droplets during electrospray ionization

“…After these emission "bursts", the charge-depleted residual parent returns to an approximately spherical shape [15,16,18]. Repeated evaporation and breakup of the fission products ultimately result in the formation of nanometer-sized droplets from which gas-phase analyte ions are produced [1].Progeny droplets are formed predominantly from the outermost layers of their parent, leading to an enrichment of species with high surface affinity [13,19,20]. In contrast, compounds with low surface affinity accumulate in the charge-depleted residual parent, from where ionization is inefficient [21,22].…”

“…Progeny droplets are formed predominantly from the outermost layers of their parent, leading to an enrichment of species with high surface affinity [13,19,20]. In contrast, compounds with low surface affinity accumulate in the charge-depleted residual parent, from where ionization is inefficient [21,22].…”