Quantitative Analysis and Determination of Molecular Weight of siRNA Type Oligonucleotides by LCMS™-8060

Importance of the Topic

Nucleic acid therapeutics are gaining prominence due to their ability to modulate gene expression at the RNA level. Among these, siRNA oligonucleotides require precise quantification and mass verification during drug development and quality control. Sensitive and accurate analysis of these molecules is crucial for evaluating pharmacokinetics, ensuring batch consistency and supporting regulatory compliance.

Objectives and Study Overview

This study aimed to demonstrate a reliable method for quantitative analysis and molecular weight determination of double-strand siRNA oligonucleotides using a Shimadzu LCMS-8060 triple quadrupole mass spectrometer. Key goals included establishing calibration curves in a femtomole range and validating molecular weight measurements via spectral deconvolution.

Methodology and Instrumentation

A reverse phase ion pair LC method was developed on a Nexera system equipped with a C18 column (100 × 2.1 mm, 1.7 µm). The mobile phase comprised 200 mM 1,1,1,3,3,3-hexafluoro-2-propanol with 7.5 mM triethylamine in water and methanol. A linear gradient from 4 % to 20 % methanol over 8 minutes at 75 °C and a flow rate of 0.2 mL/min was applied.
Instrumentation

• LC system Nexera with C18 column
• LCMS-8060 triple quadrupole mass spectrometer
• ESI source in negative ion mode
• SIM acquisition at m/z 1659.9 and 1666.0
• Q3 scan range m/z 500–1800

Main Results and Discussion

Selected ion monitoring provided linear calibration from 1 to 10 000 fmol for both sense and antisense oligonucleotides. Limits of detection and quantitation were 1 fmol and 5 fmol, respectively, corresponding to approximately 3 ng/mL for a 10 µL injection. Coefficients of determination exceeded 0.995. Multiple reaction monitoring was less sensitive, failing to detect the 5 fmol calibration point. Spectral deconvolution using LabSolutions software yielded average molecular weights of 6645.6 Da for the antisense strand and 6667.1 Da for the sense strand, with mass errors below 2 Da.

Benefits and Practical Applications of the Method

This workflow enables ultra-sensitive quantitation of siRNA oligonucleotides in a simple SIM experiment, facilitating pharmacokinetic studies and manufacturing quality control. The ability to determine molecular weight accurately with a triple quadrupole instrument expands its utility beyond quantitation, reducing the need for additional high-resolution measurements.

Future Trends and Opportunities

Advances in ion pair reagents and chromatographic media may further enhance separation efficiency. Emerging high-sensitivity detectors and optimized ESI sources could push detection limits into the attomole range. Integration of automated data processing and real-time deconvolution tools will streamline workflows for genomic medicine applications. The combination of high-throughput LC–MS platforms with bioinformatics is poised to accelerate oligonucleotide therapeutic development.

Conclusion

The presented SIM-based LCMS-8060 method offers robust quantitation and reliable molecular weight determination of siRNA oligonucleotides in the femtomole range. It provides a cost-effective alternative to high-resolution instruments for both analytical laboratories and the pharmaceutical industry.

Reference

M. Yamada Quantitative Analysis and Determination of Molecular Weight of siRNA Type Oligonucleotides by LCMS-8060 Shimadzu Application News No C219 First Edition Aug 2020