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How to read a vendor's mass spec report.

A walkthrough of what each section of a mass spectrometry report means, where the lies hide, and how to validate the result against the published molecular weight.

May 7, 20265 min#sourcing#field-guide#coa#testing

On this page · 4 sections

What mass spec actually measures
The 4 sections of a typical MS report and what to check
Common falsification patterns
When in doubt

A mass spec () report is the closest thing to physical proof of identity for a . It's also dense — 4 pages of charts and tables most buyers skim past. Here's the read order that surfaces the truth or the lie in 90 seconds.

What mass spec actually measures

ionizes the molecule, fragments it, and measures the mass-to-charge ratio (m/z) of the ions. The math is unfakeable: if the peptide has molecular weight 1419.55 Da and singly-charged ions, the spectrum shows a peak at m/z = 1420.55. Multi-charged ions show fractional masses (m/z = 710.78 for z=2, etc.). The instrument can't be tricked into reporting the wrong mass for a real molecule it actually saw.

The lie, when there's one, is in what the lab tested — not in the mass measurement itself.

The 4 sections of a typical report and what to check

1. Sample identification

Vendor name + lot/batch number. Must match the vial label. If the report identifies a different lot than the vial, the report belongs to someone else's batch.
Date of analysis. Should be within 12 months of the batch manufacture date. Reports older than that don't tell you about current vials.
Lab info. Name, address, lab director credentials. Search the lab. Real labs have a web presence, ISO certifications, scientific publications.

2. Method section

Look for: ionization method (ESI is most common for peptides; MALDI is the alternative), instrument type (Q-TOF, Orbitrap, FT-ICR are real high-res instruments; "single-quad " is lower-res but still legitimate), and sample preparation steps.

Red flag:

"Direct infusion ESI-" with no explanation of preparation. That's a method shortcut some labs use to make the report cheaper — works for a quick ID check but doesn't tell you about purity.

Green flag:

"LC-" or "-MS" — the sample was first separated by HPLC, then mass-spec'd. This catches impurities that direct infusion would miss.

3. Results / chromatogram

This is where the truth lives. Two things to verify:

A. Reported m/z matches expected molecular weight

Look up the 's published MW (Wikipedia, PubChem, the manufacturer spec). For singly-charged ions, m/z = MW + 1.008 (the proton). For doubly-charged, m/z = (MW + 2×1.008) / 2.

Examples: - BPC-157: MW 1419.55. Expected [M+H]+ = 1420.55. Doubly-charged [M+2H]2+ = 710.78. - Tirzepatide: MW 4813.4. Singly-charged is too heavy for many instruments — expect [M+5H]5+ = 963.68 or similar multi-charge. - Semaglutide: MW 4113.6. Expect multi-charge peaks.

If the reported m/z doesn't match the expected ions for the labeled , the molecule is wrong. Period. Walk away.

B. Other peaks in the spectrum

A clean preparation shows the expected M+H peak (and maybe its multi-charge variants) plus low-level isotope peaks. A messy preparation shows additional unrelated peaks at other m/z values, which means impurities, degradation products, or contamination.

Good report: "M+H peak at 1420.55 (matches BPC-157 MW 1419.55), isotope envelope present, no significant impurity peaks above 5% of base peak."

Bad report: M+H peak present BUT a second peak at 1450 with 30% of the base peak intensity. Something else is in the vial in significant quantities.

4. Interpretation / conclusion

The lab's written summary. Should clearly state: identity confirmed, purity estimate (if was run), any anomalies. "Sample matches BPC-157 reference at 98% purity, no significant impurities detected" is a clean conclusion. Vague language like "sample is consistent with BPC-157" with no purity number suggests the lab saw something they didn't want to commit to.

Common falsification patterns

1. Photoshopped m/z values on a real spectrum

Hard to detect without the raw data. Counter: if the m/z value the report claims (say 1420.55) doesn't fall on any actual peak in the printed chromatogram, it's been edited. Zoom in.

2. Reused chromatograms across multiple batches

Compare reports from the same vendor across different batches. If the chromatogram baseline noise pattern is identical, they reused the scan.

3. Cropped reports

Real reports show the full m/z range. Reports cropped to only show the expected peak hide impurity peaks at other masses.

4. PDF metadata reveals editing software

Open the PDF, check Document Properties → Producer / Author. If the report was last edited in Photoshop or saved by the vendor, that's manipulation evidence.

When in doubt

Email the lab directly with the lot number. Real labs verify their own reports. Fake labs don't respond, or respond from a Gmail address with no signature.

A legitimate vendor's mass spec report passes all four sections. A faked one usually has a tell within 90 seconds of looking at the right places.