Coupling Charge Reduction Mass Spectrometry to Liquid Chromatography for Complex Mixture Analysis

Abstract

Electrospray ionization (ESI) of solution mixtures often generates complex mass spectra, even following liquid chromatography (LC), due to analyte multiple charging. Multiple charge state distributions can lead to isobaric interferences, mass spectral congestion, and ambiguous ion identification. As a consequence, data interpretation increases in complexity. Several charge reduction mass spectrometry (MS) approaches have been previously developed to reduce the average charge state of gaseous ions; however, all of these techniques have been restricted to direct infusion MS. In this study, synthetic polyols and surfactants separated by liquid chromatography and ionized by positive mode ESI have been subjected to polonium-210 α-particle radiation to reduce the average charge state to singly charged cations prior to mass analysis. LC/MS analysis of 5000 molecular weight poly(ethylene glycol) (PEG5000) generated an average charge state of 5.88+; whereupon, liquid chromatography/electrospray ionization/charge reduction/mass spectrometry (LC/CR/MS) analysis of PEG 5000 generated an average charge state of 1.00+. The PEG5000 results demonstrated a decrease in spectral complexity and enabled facile interpretation. Other complex solution mixtures representing specific MS challenges (i.e., competitive ionization and isobaric ion overlap) were explored and analyzed with LC/CR/MS to demonstrate the benefits of coupling LC to CR/MS. For example, polyol information related to initiator, identity/relative amount of monomer, and estimated molecular weight was characterized in random and triblock ethylene oxide/propylene oxide polyols using LC/CR/MS. LC/CR/MS is a new analytical technique for the analysis of complex mixtures.

Overcharging Effect in Electrospray Ionization Mass Spectra of Daunomycin-Tuftsin Bioconjugates

“…Numerous methods for reducing the number of charges has been developed in the last few years. Ion/ion gas-phase reactions [29], 210 Po α-particle source-based charge reduction [30,31], and interface acid vapor leak-in [32] have already been used successfully for multiply-charged proteins. Charge reduction can also be achieved by using basic buffer salts, such as ammonium acetate, or solution additives with strong gas-phase basicities that can decrease the acidification during ionization [33].…”

Recent Developments in Gas-Phase Ion/Ion Reactions for Analytical Mass Spectrometry

“…Recently, there have been several reports of modified or repurposed commercial ionization sources used for front-end ion/ion reactions. [11][12][13] Two reports of instrumentation highly analogous to that described by L. M. Smith and coworkers 14,15 involved the modification of commercial ionization sources. In one report, the ESI source of a LC/MS platform was outfitted with a polonium-210 ( 210 Po) α-particle source.…”

“…Other ion/ion charge reduction strategies have been reported for polymer characterization, though it is unclear if the charge reduction occurs via proton transfer. 11,17 Most examples described above (i.e. product ion analysis and polymer analysis) utilize proton transfer reactions to charge reduce analyte ions to mainly the 1+ charge state.…”

Funktionelle Polymere mittels kontrollierter Polymerisationstechniken: Von der Massenspektrometrie endfunktionalisierter Polymere und den mechanischen Eigenschaften photovernetzbarer Blockcopolymere

“…2.9). [86][87][88][89][90] Die Coronaentladung hat dabei den Vorteil, dass keine radioaktive Quelle benötigt wird und dass das Ausmaß der Ladungsreduzierung durch die variable Spannung einge-2 Theorie und Kenntnisstand stellt werden kann. Eine Photoionisationsquelle und die Zugabe eines geeigneten Dopantmoleküls können ebenfalls zur Ladungsreduzierung der Ionen innerhalb des Elektrosprays verwendet werden.…”

“…[91] Mit diesen Methoden ist es möglich einfach geladene Ketten des Poly(ethylenglycol)s (PEG) mit mittleren Molmassen von 5-10 kg mol -1 zu erzeugen. [88,91] Abb. 2.9.…”