Everything you need to know
Research peptides require multiple types of analytical testing to confirm they are what they are claimed to be, at the purity level claimed, and free from safety-critical contaminants. This guide covers the full testing suite for research peptide manufacturers and distributors — purity, identity, endotoxin, and beyond.
What tests should a research peptide COA include?
A complete research peptide COA should include: Purity by RP-HPLC — quantifies the target peptide peak as a percentage of total peak area at 220 nm; the industry standard for purity claims (≥95% or ≥98%). Identity by LC-MS — confirms molecular weight matches the theoretical mass of the claimed sequence within analytical tolerance (±0.1 Da). Water content by Karl Fischer — relevant for lyophilized peptides sold by mass, where water content affects actual peptide yield. Endotoxin (LAL) — critical for any peptide intended for injection; typically ≤1 EU/mg. Sterility — required for sterile-grade peptides.
What is HPLC purity testing for peptides?
HPLC purity is determined by reverse-phase HPLC (RP-HPLC) with UV detection at 220 nm. The peptide sample is separated on a C18 column using an acetonitrile/water gradient with TFA modifier. The detector measures absorbance at 220 nm, which is sensitive to the peptide bond (amide bond). Purity is calculated as the target peptide peak area divided by the total integrated peak area, expressed as a percentage. Related substances (truncated sequences, des-amidated forms, oxidized variants) appear as separate peaks. Most research peptides are sold at ≥95% or ≥98% purity by HPLC.
What is LC-MS identity testing and why is it important?
LC-MS identity testing uses mass spectrometry to confirm the molecular weight of the peptide matches its theoretical value. In electrospray ionization (ESI), peptides form multiply-charged ions — the observed m/z values are used to calculate the neutral molecular mass, which is then compared to the theoretical mass calculated from the amino acid sequence. This confirms: (1) the correct peptide sequence was synthesized; (2) no major sequence errors occurred; (3) expected post-translational or protecting group chemistry is correct. Without LC-MS confirmation, a high-purity HPLC result could still represent the wrong peptide.
What endotoxin limit applies to research peptides?
There is no single universal regulatory limit for endotoxins in research peptides — unlike pharmaceutical products, research peptides are not regulated by FDA as drugs. However, common industry thresholds used by research peptide manufacturers and distributors are: <1 EU/mg for peptides likely to be used in injection studies; <5 EU/mg for less sensitive research applications. The appropriate limit depends on the route of administration and the model system. For human use (even in research contexts), stricter limits apply. We test against your stated specification.
What is the difference between pharmaceutical grade and research grade peptides from a testing perspective?
The distinction is primarily about regulatory oversight and testing scope, not chemistry. Pharmaceutical grade: manufactured under GMP, tested to USP/BP specifications, endotoxin tested by BET, sterility tested, fully documented batch records for regulatory submission. Research grade: not required to meet GMP standards, typically tested for purity and identity only, endotoxin testing optional, sold for non-clinical research use only. The underlying analytical methods (RP-HPLC, LC-MS, LAL) are the same for both; pharmaceutical grade simply requires more of them with tighter documentation standards.
How do I read the purity result on a peptide COA?
On a peptide COA, HPLC purity is expressed as a percentage: for example, "Purity: 97.3% (by HPLC)". This means 97.3% of the total UV-absorbent material in the HPLC run corresponds to the main peak (your target peptide). The remaining 2.7% represents related impurities — truncated sequences, oxidized variants, or other synthesis byproducts. A COA should also show the chromatogram or at minimum the integration table so you can see whether impurities are one large peak or many small ones. Order peptide purity and identity testing.