Modeling cationic adduction of oligonucleotides using electrospray desorption ionization

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Biochemistry

Background:

• Cationic adduction in mass spectrometry (MS) reduces sensitivity and increases spectral complexity for oligonucleotides.
• Alkylamines are used to mitigate cationic adduction, but the influence of their physiochemical properties remains unclear.

Purpose of the Study:

• To investigate the impact of alkylamine physiochemical properties on reducing cationic adduction during MS analysis.
• To develop predictive models for selecting optimal alkylamines to enhance MS sensitivity and spectral clarity.

Main Methods:

• Samples were analyzed using a Synapt G2 HDMS quadrupole time-of-flight (TOF) hybrid mass spectrometer.
• Negative ion electrospray ionization mode was employed with direct infusion at a flow rate of 50 μL/min.
• TOFMS parameters were optimized, including capillary voltage, cone voltage, and temperatures.

Main Results:

• A quantitative model was developed to predict optimal alkylamines, identifying proton affinity, gas-phase basicity, and pKa as key properties.
• A qualitative model highlighted physiochemical properties influencing adduction reduction, including boiling point, molecular weight, Henry's Law Constant, and logP.
• The quantitative model successfully predicted cationic adduction trends for RNA (microRNA) and phosphorothioate samples.

Conclusions:

• Two models were established to elucidate the physiochemical drivers of adduction and guide alkylamine selection.
• These models offer a mathematical tool for users to predict the most effective alkylamine for reducing cationic adduction.
• The findings aim to decrease spectral complexity and enhance sensitivity in mass spectral analysis.