Submicrometer Nanospray Emitters Provide New Insights into the Mechanism of Cation Adduction to Anionic Oligonucleotides

Abstract

The electrospray-MS analysis of oligonucleotides is hampered by non-volatile metal cations, which may produce adducts responsible for signal suppression and loss of resolution. Alternative to replacing metal cations with MS-friendly ammonium, we explored the utilization of nanospray emitters with submicrometer-diameter tips, which was shown to benefit the analysis of protein samples containing elevated salt concentrations. We demonstrated that such benefits are not limited to proteins, but extend also to oligonucleotide samples analyzed in the negative ion mode. At elevated Na + /Mg 2+ concentrations, submicrometer tips produced significantly greater signal-tonoise ratios, as well as greatly reduced adducts and salt clusters, than observed when utilizing micrometer tips. These effects were marginally affected by emitter composition (i.e., borosilicate versus quartz), but varied according to salt concentration and number of oligonucleotide phosphates. The results confirmed that adduct formation is driven by the concentrating effects of the desolvation process, which leads to greatly increased solute concentrations as the volume of the droplet decreases. The process promotes cation-phosphate interactions that may not have necessarily existed in the initial sample, but nevertheless shape the observed adduct series. Therefore, such series may not accurately reflect the distribution of counter-ions surrounding the analyte in solution. No adverse effects were noted on specific metal interactions, such as those present in a model drug-DNA assembly. These observations indicate that the utilization of submicrometer tips represents an excellent alternative to traditional ammonium-replacement approaches, which enables the analysis of oligonucleotides in the presence of Na + /Mg 2+ concentrations capable of preserving their structure and functional properties.

Modeling cationic adduction of oligonucleotides using electrospray desorption ionization

“…These tenets help to shape our understanding of the physiochemical properties of the electrospray solution and provide a rationale for increasing sensitivity and decreasing the complexity of spectra. Salt solutions can be useful in biological applications to study secondary structures of natively sprayed oligonucleotides . While this provides useful structurally relevant biological information, cationic adduction caused by these salt solutions is generally undesirable due to the significant decrease in signal sensitivity and the increased spectral complexity.…”

“…Salt solutions can be useful in biological applications to study secondary structures of natively sprayed oligonucleotides. [4][5][6] While this provides useful structurally relevant biological information, cationic adduction caused by these salt solutions is generally undesirable due to the significant decrease in signal sensitivity and the increased spectral complexity.…”

A microdroplet-accelerated Biginelli reaction: mechanisms and separation of isomers using IMS-MS

“…Recently, the groups of Cooks, [17][18][19][20][21][22][23][24][25][26] Zare, [27][28][29][30][31][32][33][34][35][36][37][38][39] and others [40][41][42][43][44][45][46] have reported the acceleration of reactions in microdroplet environments during the process of electrospraying reagents into a mass spectrometer. 32 Intrigued by the possibility of faster rates for multicomponent reactions, we explored the use of microdroplets as a means of enabling a rapid Biginelli reaction (Scheme 2).…”

High‐resolution ion mobility spectrometry‐mass spectrometry of isomeric/isobaric ribonucleotide variants

“…Analyses were performed on either a modified SYNAPT G2‐S i instrument equipped with the cIM separator (Scheme ) or a standard SYNAPT G2 HDMS, both from Waters Corporation (Wilmslow, UK). The analyses performed on the SYNAPT G2 HDMS were accomplished in static nanospray mode by using quartz emitters prepared in‐house as described in Kenderdine et al . A stainless‐steel wire was inserted into the emitter back end to provide typical spray voltages in the 0.9 to 1.2‐kV range.…”

“…The analyses performed on the SYNAPT G2 HDMS were accomplished in static nanospray mode by using quartz emitters prepared in-house as described in Kenderdine et al . 41 A stainless-steel wire was inserted into the emitter back end to provide typical spray voltages in the 0.9 to 1.2-kV range. Source temperature and desolvation voltages were finely adjusted by monitoring the incidence of ammonium adducts and water clusters.…”