Formation of unexpected ions from a first‐generation polyamidoamine dendrimer by use of methanol: an artefact due to electrospray emitter corrosion?

Abstract

We report the formation of unexpected ions during the analyses of a first-generation polyamidoamine dendrimer in negative ion mode using an ion trap equipped with an electrospray ionisation source. These surprising ions corresponded to an increase of 12 m/z units over those expected. The formation of the unexpected ions was dependent on the tuning of the solution flow rate and the capillary high voltage. In addition, measurements of unusual value of the current suggested that a reaction was occurring in the corona plasma. The influence of methanol in this phenomenon was demonstrated by using CD(3)OH in the sample preparation. We propose two structures to explain the observed adduct based on the results of MS(2) experiments and by referring to previous work dealing with 12 m/z units addition. We showed that a corona discharge caused by alterations taking place to the electrospray capillary emitter was the origin of these unexpected ions. Finally, we discuss the mechanism involved in the formation of the ions and we propose means to control such artefacts.

Desulfurization of phosphorothioate oligonucleotides via the sulfur‐by‐oxygen replacement induced by the hydroxyl radical during negative electrospray ionization mass spectrometry

“…In the course of negative ESI, however, the heterogeneous electron transfer from neutral species to the negative electrospray emitter is not expected to occur. In addition, the corona discharge is expected to occur more readily in the negative ion mode than in the positive ion mode . Therefore, one most likely rationale is that the occurrence of desulfurization of phosphorothioate oligonucleotides is induced by •OH during negative ESI‐MS.…”

Identification and quantification of poly(amidoamine) PAMAM dendrimers of generations 0 to 3 by liquid chromatography/hybrid quadrupole time‐of‐flight mass spectrometry in aqueous medium

“…As the production of PAMAMs is based on divergent synthesis, the most probable fragmentation pathway was via a retro‐Michael reaction. Most of the investigations on structure defects or metal/ion complexes that were carried out using a unit mass resolution spectrometer in full scan and MS/MS modes proposed that the dendrimer precursor ions fragmented via retro‐Michael reactions, in both positive and negative ionization mode . He and McLuckey demonstrated that ion/ion proton transfer reactions facilitated the interpretation of the product ion mass spectra of PAMAM generation 0.5, through manipulation of the charge states of the PAMAM precursor ions to form lower charge states than those initially formed by ESI.…”

Charge inversion via concurrent cation and anion transfer: application to corticosteroids

“…The chloride ion transferred to the steroid upon charge inversion must originate from the reagent anion population, presumably due to adventitious salts in the electrospray solution, if the reactions proceed via process (1) of Scheme . Full‐generation PAMAM dendrimers have been shown previously to adduct chloride ions in the negative ion mode to form singly charged anions 37. The full‐generation dendrimers are terminated in amino groups and therefore lack the ability to bind anions via proton‐ or metal‐ion‐bound interactions.…”