A Certificate of Analysis (COA) is a document produced by an analytical laboratory that reports the measured properties of a specific lot of material. For peptide reference materials, a third-party COA is the primary record of identity and purity. This article explains the assays commonly listed on a COA and what each one measures.
HPLC purity
High-Performance Liquid Chromatography (HPLC) separates the components of a sample and reports the target peptide as a percentage of the total. A purity figure such as 99% indicates the proportion of the sample attributable to the intended peptide relative to related impurities. The chromatogram accompanying the figure shows the separation as a series of peaks.
Mass spectrometry (identity)
Mass spectrometry measures the molecular mass of the peptide, which is compared against the theoretical mass calculated from its amino-acid sequence. A close match confirms that the material has the expected molecular identity. This assay answers a different question than HPLC: identity (is this the right molecule?) rather than purity (how much of the sample is that molecule?).
Other common assays
- Appearance — a visual description of the lyophilized powder.
- Peptide content / net peptide — the fraction of the mass that is peptide versus counter-ions and residual moisture.
- Sterility and endotoxin — where reported, these describe microbial and endotoxin testing of the lot.
- Heavy metals — screening for elemental contaminants.
Matching a COA to a lot
A COA applies to the specific lot number it names. When documenting research, match the lot number on the vial to the lot number on the COA so that the reported figures correspond to the material actually in hand. PureDose Labs publishes third-party testing documentation on its Testing & Documentation page.
Frequently asked questions
What is a peptide Certificate of Analysis?
A Certificate of Analysis, or COA, is a document produced by an analytical laboratory that reports the measured properties of one specific lot of material. For peptide reference materials, a third-party COA is the primary record of identity and purity, listing the assays performed and the result of each measurement.
What does HPLC purity report on a COA?
High-Performance Liquid Chromatography separates the components of a sample and reports the target peptide as a percentage of the total. A figure such as 99% indicates the proportion attributable to the intended peptide relative to related impurities. The accompanying chromatogram shows that separation as a series of peaks.
How does mass spectrometry confirm identity?
Mass spectrometry measures the molecular mass of the peptide and compares it against the theoretical mass calculated from its amino-acid sequence. A close match confirms the material has the expected molecular identity. This answers a different question than purity: whether the sample is the right molecule at all.
Why should I match the lot number to the COA?
A Certificate of Analysis applies only to the specific lot number it names. Matching the lot number on the vial to the lot number on the COA ensures the reported purity and identity figures correspond to the material actually in hand rather than to a different production run.
What is the difference between purity and net peptide content?
HPLC purity describes the proportion of the intended peptide relative to related impurities. Net peptide content describes the fraction of the total mass that is peptide versus counter-ions and residual moisture. They are separate measurements that answer different questions about a given lot of material.