MS Interpretation Guide¶

Field	Value
Document ID	RPL-GUIDE-MS-001
Version	1.0
Publisher	RPL Peptide (Qingdao RPL Biotechnology Co., Ltd.)
URL	https://rplpeptides.com/guides/peptide-ms-interpretation-guide
Last Updated	July 2026

1. Introduction¶

Mass spectrometry provides precise molecular weight determination, confirming peptide identity. Electrospray Ionization (ESI) is the standard method for peptides.

2. Molecular Weight¶

Theoretical MW: Calculated from amino acid sequence. Observed MW: Measured by MS. Acceptable difference: ±0.5 Da.

3. Charge States¶

ESI produces multiple charge states (protonated species). Example for MW 4000 Da: [M+3H]³⁺ at m/z 1334 [M+4H]⁴⁺ at m/z 1001 [M+5H]⁵⁺ at m/z 801

4. Peak Assignment¶

Each charge state peak should be: - Well-resolved - The correct m/z for the assigned charge - Consistent across adjacent charge states

5. Identity Confirmation¶

Confirmed when: - Observed mass matches ±0.5 Da - Charge state distribution is typical - No unexpected major peaks

6. Common Spectra¶

Typical features: - Strong charge state envelope - Clean spectrum (few impurities) - Expected isotopic distribution

7. Typical Questions¶

Q: What is [M+16]? A: Oxidation (+16 = oxygen atom added). Q: What is [M-18]? A: Loss of water (dehydration). Q: What if masses don't match? A: Check counter-ion effects.

Document Revision History¶

Version	Date	Changes
1.0	July 2026	Initial release

rplpeptides.com