Mass Spectrometry
Mass Spectrometry for Peptides
Mass spectrometry (MS) provides definitive molecular weight confirmation and structural characterization of peptides.
Ionization Techniques
Electrospray Ionization (ESI)
- Mechanism: Produce multiply charged ions from solution
- Typical charge states: [M+2H]2+, [M+3H]3+, [M+4H]4+
- Compatibility: Directly coupled with HPLC (LC-MS)
Matrix-Assisted Laser Desorption (MALDI)
- Advantage: Primarily singly charged ions, simpler spectra
- Matrix choices: CHCA, DHB, sinapinic acid
Common Mass Modifications
| Modification | Mass Change | Observation |
|---|---|---|
| <strong>Oxidation (Met)</strong> | +15.995 Da | Common artifact |
| <strong>Dehydration</strong> | -18.011 Da | Aspartimide formation |
| <strong>Acetylation</strong> | +42.011 Da | N-terminal cap |
| <strong>Sodium adduct</strong> | +21.982 Da | [M+Na]+ vs [M+H]+ |
Instrument Platforms
| Platform | Resolution | Accuracy | Best For |
|---|---|---|---|
| <strong>Triple Quad</strong> | Unit mass | +/-0.5 Da | Quantitative analysis |
| <strong>Q-TOF</strong> | 20,000-40,000 | +/-5 ppm | Structure elucidation |
| <strong>Orbitrap</strong> | >100,000 | <3 ppm | High-res characterization |
| <strong>TOF-TOF</strong> | 10,000-20,000 | +/-10 ppm | MALDI sequencing |
See [[HPLC Analysis]], [[Peptide Science Overview]], [[Amino Acid Reference]]