> For the complete documentation index, see [llms.txt](https://docs.rplpeptides.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rplpeptides.com/docs/guides/peptide-ms-interpretation-guide.md).

# 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 |

***

© 2026 RPL Peptide

rplpeptides.com


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