HPLC Testing Explained
High Performance Liquid Chromatography (HPLC) is the standard method for measuring peptide purity. It separates the target peptide from impurities based on their chemical properties, quantifying the percentage of the sample that is the desired product.
Key Points
Step-by-Step Guide
Understand HPLC Principles
The sample is dissolved and pushed through a column packed with silica particles. Different molecules travel at different speeds based on their interaction with the column. A UV detector measures what comes out over time, producing a chromatogram.
Read an HPLC Trace
The chromatogram shows peaks at different retention times. The tallest peak should be your target peptide. Smaller peaks are impurities. Purity = (area of main peak / total area of all peaks) x 100%.
Evaluate Purity Claims
98%+ is excellent. 95-98% is good. 90-95% is marginal. Below 90% is poor quality. These thresholds are industry norms for research-grade peptides.
Know Method Variables
HPLC conditions (column type, gradient, wavelength) affect results. Results from different labs using different methods may vary slightly. Consistent methodology within a vendor is more important than absolute numbers.
Warnings & Precautions
- !Different HPLC methods can give different purity numbers for the same sample.
- !UV-inactive impurities may not be detected.
- !HPLC measures chemical purity, not sterility or endotoxin levels.
- !A single HPLC run represents one measurement—batch consistency requires multiple tests.
Frequently Asked Questions
What do HPLC impurity peaks represent?
Small peaks represent synthesis byproducts: deletion sequences (missing amino acids), truncated chains, oxidized variants, and residual chemicals. Most are biologically inactive but may cause unintended effects at injection.
Why does purity vary between vendors?
Synthesis skill, raw material quality, purification thoroughness, and quality control standards all vary. Higher purity costs more to produce, which is why premium vendors charge more. The cheapest vendor often has the lowest purity.
Can HPLC detect the wrong peptide?
HPLC measures purity but not identity. A vial could be 99% pure of the wrong peptide. Mass spectrometry is needed to confirm identity. This is why both HPLC and MS on a COA are important.