October 1, 2026
HPLC vs Mass Spectrometry: How Peptide Purity Is Verified
For laboratory research use only. This article explains analytical methods used to characterize research peptides.
Peptide purity is verified with two complementary tests: high-performance liquid chromatography (HPLC) measures how much of a sample is the target peptide, and mass spectrometry (MS) confirms that it is the target peptide. Neither test is enough on its own. This guide explains what each method measures, how to read the results on a Certificate of Analysis, and which impurities they catch.
Why one test is not enough
A peptide sample can be “99% pure” by HPLC and still be the wrong molecule if a synthesis error produced a single, clean impurity. Equally, a sample can show the correct mass by MS while containing significant amounts of truncated or deleted sequences. Using both methods closes each gap. A review of peptide impurities in pharmaceutical products catalogs these failure modes in detail (D’Hondt et al., 2014).
HPLC: measuring purity
How it works
Reversed-phase HPLC pushes a dissolved sample through a column packed with hydrophobic material. Each component of the sample travels through at a different speed depending on how strongly it interacts with the column, then passes a UV detector (typically at 214–220 nm, where peptide bonds absorb). The result is a chromatogram: a plot of detector signal over time.
How to read the chromatogram
- Main peak: the target peptide. Its area as a percentage of total peak area is the reported purity.
- Minor peaks: impurities eluting before or after the main peak.
- Retention time: when the main peak appears; it should be consistent between batches run under the same method.
A purity of ≥99% means at least 99% of the UV-absorbing material in the sample is the main peak.
Mass spectrometry: confirming identity
How it works
Mass spectrometry ionizes the peptide — usually by electrospray ionization (ESI) or MALDI — and measures the mass-to-charge ratio (m/z) of the resulting ions. Peptides often carry several charges, so ESI spectra show a series of peaks that are deconvoluted into a single molecular mass.
How to read the result
Compare the observed mass to the theoretical mass calculated from the sequence. For example, BPC-157 has a theoretical mass of about 1,419 Da. A match within the instrument’s tolerance confirms identity; a mass shifted by the weight of one amino acid suggests a deletion or insertion.
Common impurities and which test catches them
| Impurity type | Origin | HPLC | MS |
|---|---|---|---|
| Deletion sequences (missing residue) | Incomplete coupling during synthesis | Often a separate peak | Lower mass |
| Truncated sequences | Chain termination | Separate peak | Lower mass |
| Incomplete deprotection | Protecting group left attached | Separate peak | Higher mass |
| Oxidation (e.g., Met, Trp) | Handling and storage | Small shifted peak | +16 Da |
| Deamidation (Asn, Gln) | Moisture, pH, time | Close-eluting peak | +1 Da |
| Racemization (D-isomers) | Synthesis conditions | Sometimes co-elutes | Same mass — not detected |
The last row is why HPLC method quality matters: some impurities share the target’s mass and can only be separated chromatographically.
What a complete Certificate of Analysis should show
- Product name, sequence and lot number matching the vial
- HPLC chromatogram with integrated peak table and purity percentage
- Mass spectrum with observed vs. theoretical mass
- Test date and the laboratory that performed the analysis
For a walkthrough of each COA field, see Understanding COA documentation in research compound sourcing. Storage also affects purity over time — oxidation and deamidation increase with heat and moisture, as covered in why storage conditions matter.
How BioRhex verifies every batch
Every BioRhex compound is synthesized in a GMP-compliant US facility and tested by independent third-party laboratories using HPLC purity analysis and mass spectrometry identity confirmation. Batches below the ≥99% purity threshold are not released, and each order ships with a batch-specific COA. Browse all research peptides.
References
- D’Hondt M, Bracke N, Taevernier L, et al. (2014). Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis, 101, 2–30. https://doi.org/10.1016/j.jpba.2014.06.012