Adduct formation by coeluting endogenous biomolecules using ESI-MS : A comprehensive study on ESI efficiency.

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Chromatography

Background:

• Liquid chromatography-mass spectrometry (LC-MS) is vital for analysis.
• Electrospray ionization (ESI) is a common technique, but ionization mechanisms and signal interferences like ion suppression are not fully understood.

Purpose of the Study:

• Investigate adduct formation impacting hydrochlorothiazide detection in negative mode ESI.
• Identify adduct partners and elucidate factors influencing adduct formation.

Main Methods:

• LC-MS analysis using negative mode ESI.
• Systematic variation of coeluting compound concentrations (hippuric acid, indoxyl sulfate).
• Comparison of ESI with atmospheric pressure chemical ionization (APCI) and different ESI sources.
• Testing various mobile phase compositions.
• Analysis of structurally related and unrelated compounds.

Main Results:

• Adduct formation of hydrochlorothiazide with hippuric acid and indoxyl sulfate was observed, reducing the target analyte signal.
• Adduct formation was specific to ESI, independent of source design and mobile phase composition.
• Formation was concentration-dependent, with an over-additive signal loss effect when both adducts formed.
• Similar adduct formation occurred with structurally related diuretics (bendroflumethiazide, buthiazide, cyclopenthiazide) and dorzolamide.

Conclusions:

• Adduct formation is a significant source of signal suppression in ESI for certain compounds.
• Understanding these adducts is crucial for accurate quantitative LC-MS analysis.
• The findings offer new insights into ESI ionization mechanisms.