HPLC Purity Testing

HPLC Purity Testing: How Stackpure Validates Every Batch

Lab Methodology

A technical overview of HPLC methodology as applied to research peptide purity testing, including column selection, gradient conditions, peak integration, and how to interpret a Stackpure Certificate of Analysis.

For in vitro research use only. Not medical advice. Not dosing guidance.

What HPLC Measures

High-Performance Liquid Chromatography (HPLC) is the industry standard for measuring the purity of synthetic peptides. The technique separates a sample's molecular components by differential affinity to a stationary phase (column packing material) under mobile phase flow. For peptide purity testing, Reverse-Phase HPLC (RP-HPLC) is used: the stationary phase is hydrophobic (typically C18, octadecylsilyl), and peptides are separated by hydrophobicity. More hydrophobic components elute later in a water/organic solvent gradient. UV absorbance at 214 nm, where the peptide bond absorbs, is used for detection and quantification.

RP-HPLC Conditions for Peptide Analysis

Standard conditions for research peptide purity analysis use a C18 column (e.g., 150 × 4.6 mm, 5 μm particle size), a linear gradient from 0.1% TFA in water to 0.1% TFA in acetonitrile over 20–40 minutes, a flow rate of 1 mL/min, and UV detection at 214 nm. The sample is dissolved in 0.1% TFA/water at 0.5–1 mg/mL and injected at 10–20 μL. The resulting chromatogram shows peaks for each molecular species in the sample; the area under each peak is proportional to the molar quantity of that species (assuming similar extinction coefficients at 214 nm, which is a reasonable approximation for most peptides).

Purity Calculation

Purity (%) is calculated as: (area of target peptide peak) / (sum of all peak areas) × 100. An HPLC purity of 99% means that 99% of the UV-absorbing material in the sample elutes at the expected retention time for the target peptide. The remaining 1% represents deletions, truncations, oxidised variants, and other impurities from synthesis. All Stackpure batches must achieve ≥99% purity on this measure. Note that HPLC purity is a relative measure, it does not account for inorganic salts, residual solvents, or water, which do not absorb at 214 nm.

Mass Spectrometry Confirmation

Stackpure COAs include mass spectrometry (MS) data confirming the molecular weight of the target peptide. Electrospray ionisation MS (ESI-MS) is used, which generates multiply charged ions ([M+nH]n+) for larger peptides. The measured m/z values are deconvoluted to give the molecular weight of the neutral molecule, which is compared to the theoretical MW calculated from the peptide sequence. A match within acceptable instrument tolerance (typically ±0.5 Da for ESI-TOF systems) confirms the peptide identity independently of chromatographic separation.

Reading a Stackpure COA

A Stackpure Certificate of Analysis contains: (1) product name and CAS number; (2) batch number and production date; (3) HPLC purity percentage with chromatogram image; (4) MS confirmation with observed and theoretical molecular weight; (5) the name and accreditation of the independent third-party testing laboratory. The batch number on your COA should match the batch number printed on your product label. If you cannot locate your COA, contact sales@stackpure.is with your order number and batch number.

Frequently Asked Questions

Why is 214 nm used as the detection wavelength for peptide HPLC?

The peptide bond (–CO–NH–) absorbs UV light at approximately 210–220 nm. Using 214 nm provides detection of all peptide-containing molecules regardless of side-chain composition, giving a near-universal detector response for the peptide backbone. Aromatic residues (Phe, Trp, Tyr) have additional absorbance at 254–280 nm but 214 nm captures the full peptide content.

What is the difference between HPLC purity and amino acid analysis?

HPLC purity measures the relative proportion of the target peptide among all UV-absorbing species. Amino acid analysis (AAA) hydrolyses the peptide and measures the molar ratios of each amino acid, confirming the sequence composition. Both are complementary: HPLC confirms purity and identity by retention time; AAA confirms sequence composition quantitatively. Stackpure uses HPLC + MS as its standard COA methodology.

How do I request a COA for my Stackpure order?

Email sales@stackpure.is with your order number and the batch number printed on the product label. COAs are typically returned within 24 hours on business days.