Methods
Ten determinations, each answering one question. Each has its own page stating how the measurement works, what the result means and what it cannot tell you.
| Axis | Question | Unit |
|---|---|---|
| Identity | Is the labelled compound present | Da |
| Purity | What fraction of peptide material is the target | area % |
| Content | How many milligrams are actually present | % and mg |
| Chemical safety | Metals, solvents, counter-ions | µg/g, ppm, mg |
| Biological safety | Pyrogenic or contaminated | EU, CFU, growth |
No single determination covers more than one axis of quality. A peptide reported at 99 percent chromatographic purity commonly contains 70 to 85 percent peptide by mass, carries a counter-ion load of 10 to 25 percent, and has had nothing said about it regarding endotoxin, bioburden or elemental impurities. Completeness is a matter of which determinations were ordered, not of how good any one of them is.
Identity by mass spectrometry
Is the labelled compound actually present?
Theoretical and measured mass, difference in daltons · ICH Q2(R2)
RP-HPLC-UVChromatographic purity
What fraction of the peptide-related material is the target?
Area percentage with the chromatogram attached · Area normalisation at 214 nm
Chiral HPLCEnantiomeric purity
Is the material the stated enantiomer, or its mirror image?
Enantiomeric excess as a percentage, with the chromatogram · Chiral stationary phase, ICH Q6A decision tree 5
CHNS / AAANet peptide content
How many milligrams of peptide are actually present?
Percentage and milligrams per unit · Combustion elemental analysis or amino acid analysis
LAL / rFCBacterial endotoxins
Is the material pyrogenic?
Endotoxin units per unit or per millilitre · USP <85>, USP <86>
USP <61>Microbial enumeration
What is the bioburden?
Colony forming units per gram or millilitre · USP <61>, USP <62>
USP <71>Sterility
Is the product sterile?
Growth or no growth over fourteen days · USP <71>
ICP-MSElemental impurities
Are there heavy metals, and at what concentration?
Micrograms per gram against ICH Q3D limits · USP <232>, USP <233>, ICH Q3D(R2)
GC-MSResidual solvents
What is left over from synthesis and purification?
Parts per million per solvent · USP <467>, ICH Q3C(R8)
Karl FischerWater content
How much of the mass is water?
Percentage by weight · Coulometric titration, USP <921>
IC / LC-MSTrifluoroacetate counter-ion
How much of the vial mass is counter-ion?
Percentage and milligrams per unit · Ion chromatography or LC-MS
The methods above are ordinary analytical chemistry. What separates a laboratory from an instrument is the set of controls run around them, and those are the questions worth asking of any testing provider, including this one.
System suitability before every sequence: resolution, peak asymmetry, and repeatability of retention time and area. Reagent blanks, duplicates and spiked recoveries within each batch. Calibration against certified reference materials with documented traceability. Method validation to ICH Q2(R2) for specificity, linearity, precision, accuracy, detection and quantitation limits, and robustness.
Participation in proficiency testing is the only external evidence that a laboratory's numbers are correct rather than merely reproducible. Chain of custody is recorded from receipt to disposal, and retained sample is held so a disputed result can be re-examined rather than argued about.
| LOD and LOQ | Per-analyte figures are published once method validation is complete. They are not estimated here. |
| Uncertainty | Expanded uncertainty at k = 2, stated per determination on the certificate. |
How many determinations does a complete peptide characterisation need?
Four at minimum: identity by mass, chromatographic purity, net peptide content and water. Parenteral material adds endotoxin and microbial enumeration. No single method covers more than one of the five axes of quality.
Why does every method page list what the method cannot detect?
Because a certificate that reports only findings invites the reader to treat silence as reassurance. The blind spot of a method is as material as its result.
Updated 2026-09-01