Mass and charge assignment for electrospray ions by cation adduction

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Biochemistry

Background:

• Determining ion mass (m) and charge (z) from m/z values in electrospray mass spectra is crucial.
• Traditional methods rely on multiple charge states or isotopic peaks, often requiring high resolution or specific conditions.

Purpose of the Study:

• To introduce and validate a new approach for mass and charge assignment using copper(II) ion (Cu2+) adducts.
• To demonstrate the utility of Cu2+ adduction in complex mixture analysis, including tandem mass spectrometry (MS/MS).

Main Methods:

• Utilizing the mass shift caused by replacing protons with Cu2+ ions (61.5 Da) to establish a mass scale.
• Comparing Cu2+ adduction with sodium adducts (Na+, 22.0 Da) for mass assignment accuracy and utility across different resolving powers and mass ranges.
• Investigating the stability of Cu2+ adducts during collisional dissociation in MS/MS experiments.

Main Results:

• Cu2+ adduction provides a significant mass separation, enabling accurate m and z assignment even with lower resolving power.
• The 61.5 Da mass shift from Cu2+ adduction is more effective than the 22.0 Da shift from Na+ adducts for mass determination, especially for larger molecules.
• Cu2+ adducts exhibit greater stability during collisional dissociation compared to Na+ adducts, making them more suitable for MS/MS sequence analysis.

Conclusions:

• Cu2+ adduction represents a valuable and previously unhighlighted method for assigning mass and charge in mass spectrometry.
• This technique enhances the analysis of complex samples and sequence-specific fragment ions in MS/MS studies.
• Cu2+ adduction offers improved accuracy and applicability over traditional methods, particularly for challenging samples.