Mass Spectrometry Identity Confirmation Parameters
An overview of Electrospray Ionization Mass Spectrometry (ESI-MS) for verifying the molecular weight and structural identity of synthetic peptides.
Educational reference only. Not a substitute for a validated laboratory method or lot-specific testing.
ESI-MS Principles in Peptide Analysis
Mass spectrometry supplies evidence about molecular mass and, with appropriate fragmentation methods, sequence. Electrospray ionization commonly produces multiply charged ions. Intact mass alone cannot definitively establish sequence or distinguish every isomer.
Observed mass-to-charge ratios and charge states can be used to compare the measured mass with a theoretical value. Interpretation requires calibrated instruments, stated tolerances, and assessment of possible adducts or other species.
Resolving Isotopic Envelopes
For high-molecular-weight peptides, the isotopic envelope must be carefully evaluated. The presence of naturally occurring carbon-13 shifts the observed mass.
High-resolution instruments can improve mass discrimination, but achieved accuracy depends on calibration and acquisition conditions. Isobaric and isomeric compounds may require orthogonal techniques or MS/MS; resolution does not eliminate every ambiguity.
Adduct Formation
During ionization, sodium (Na+) or potassium (K+) adducts may form. Analysts must distinguish between these predictable adducts and actual synthesis errors (e.g., incomplete deprotection).
Verification requires identifying the [M+H]+ and [M+2H]2+ species, and confirming that the deconvoluted mass matches the sequence molecular weight.