Mass Spectrometry for Peptide Analysis
Mass spectrometry (MS) is the gold standard for confirming peptide identity. By measuring the mass-to-charge ratio of ionized molecules, it confirms that a sample contains the expected peptide sequence with high precision.
Key Points
Step-by-Step Guide
Understand MS Principles
The sample is ionized, accelerated through an electromagnetic field, and separated by mass-to-charge ratio. The resulting spectrum shows peaks at specific m/z values that correspond to the molecular weight of the peptide.
Read MS Results
The key value is the observed molecular weight vs. the theoretical weight. They should match within 1 dalton. Multiple charge states may appear (e.g., [M+H]+, [M+2H]2+), showing the same molecule at different charges.
Recognize Common MS Types
MALDI-TOF: fast, simple, good for peptides 500-10,000 Da. ESI-MS: coupled with liquid chromatography (LC-MS), excellent for complex mixtures. Both are valid for peptide identification.
Understand Limitations
MS confirms molecular weight (identity) but not purity, conformation, or biological activity. Two different peptide sequences could theoretically have the same molecular weight (rare but possible). HPLC complements MS for purity assessment.
Warnings & Precautions
- !MS alone does not confirm purity—HPLC is needed.
- !Isobaric peptides (same mass, different sequence) are rare but exist.
- !Degraded peptides may still show the correct parent mass.
- !MS quality depends on instrument calibration and operator skill.
Frequently Asked Questions
What does it mean if the mass does not match?
A mass discrepancy of more than 1-2 daltons suggests: wrong peptide, modified peptide (oxidation adds 16 Da), or degradation. The vial likely does not contain what is claimed and should not be used.
Is MS or HPLC more important?
Both are essential and complementary. MS confirms identity (right peptide), HPLC confirms purity (how much is the right peptide). A peptide with correct MS but low HPLC purity contains the right molecule plus impurities.
Can I get my own peptides tested by MS?
Yes. Services like Janoshik Analytical, university core facilities, and contract analytical labs offer peptide MS testing. Costs range from $50-200 per sample depending on the analysis type.