Nanospray 'taxation' and how to avoid it

Area of Science:

• Analytical Chemistry
• Biochemistry
• Mass Spectrometry

Background:

• Nanospray ionization (NSI) is a crucial technique in mass spectrometry.
• Analyte loss and delayed detection have been observed in NSI, impacting data reliability.
• The cause of these losses, particularly concerning charged analytes, requires further investigation.

Purpose of the Study:

• To investigate the cause of analyte loss and delayed detection in NSI mass spectrometry.
• To understand the role of the capillary surface charge in analyte interactions.
• To assess the impact of these losses on protein identification and characterization.

Main Methods:

• Mass spectrometric analysis using nanospray ionization with glass and quartz capillaries.
• Cation-exchange chromatography principles applied to understand surface interactions.
• Analysis of peptide mixtures and bovine serum albumin (BSA) tryptic digests at sub-micromolar concentrations.

Main Results:

• Analyte loss and delayed detection were correlated with the negative charge on glass nanospray capillary surfaces.
• Peptides and proteins with localized positive charges, particularly blocks of basic amino acids, showed higher affinity for the glass surface.
• Approximately 20% fewer tryptic peptides were identified using glass capillaries compared to quartz or conventional electrospray.

Conclusions:

• The negative surface charge of glass nanospray capillaries causes cation-exchange interactions, leading to analyte loss.
• This phenomenon primarily affects peptides and proteins with localized positive charges.
• While general protein identification may be unaffected, detailed analyses like mutation or PTM studies could suffer from reduced sequence coverage.