Research Guide
Peptide Purity Testing Explained: HPLC, MS & Quality Grades
Peptide purity is the single most important quality metric for research compounds. It determines what percentage of the material in your vial is the intended peptide versus synthesis byproducts. Understanding how purity is measured, what different purity grades mean, and how to evaluate supplier claims is essential for reproducible research.
What Is Peptide Purity?
Peptide purity refers to the percentage of the total sample that consists of the target peptide sequence. During solid-phase peptide synthesis (SPPS), not every coupling reaction is 100% efficient. This means a portion of the final product consists of truncated sequences (missing amino acids), deletion sequences (skipped residues), or chemically modified variants (oxidized, deamidated, or racemized forms).
Purity is expressed as a percentage. A peptide with 98% HPLC purity means that 98% of the detectable material in the sample is the correct full-length peptide, and 2% consists of impurities.
How HPLC Measures Purity
High-Performance Liquid Chromatography (HPLC) is the gold standard for peptide purity analysis. The technique separates molecules based on their chemical properties (hydrophobicity, charge, size) as they pass through a chromatography column.
The output is a chromatogram — a graph showing peaks at different retention times. Each peak represents a different molecular species. The main peak (largest) is your target peptide. Smaller peaks are impurities. Purity is calculated as the area of the main peak divided by the total area of all peaks, expressed as a percentage.
Reverse-phase HPLC (RP-HPLC) with C18 columns and UV detection at 214 nm or 220 nm is the most common method for peptide purity analysis.
Purity Grades Explained
Crude (50-75%): Unpurified synthesis output. Not suitable for most research.
Desalted (>75%): Salt-removed but not fully purified. Used for antibody production and some screening assays.
Research Grade (≥95%): Standard for most laboratory research. Adequate for cell-based assays, binding studies, and in vitro experiments.
Premium Grade (≥98%): High-purity material for sensitive assays, quantitative studies, and applications where impurity interference must be minimized.
Pharmaceutical Grade (≥99%): Highest commercially available purity. Required for GLP studies and pharmaceutical development work.
Why Mass Spectrometry Is Also Needed
HPLC measures purity but cannot confirm identity. A sample could show 99% HPLC purity but actually be the wrong peptide — the wrong sequence could still elute as a single clean peak. Mass spectrometry (MS) provides the identity check by measuring the molecular weight of the compound and comparing it to the theoretical weight of the target sequence. Together, HPLC + MS provide both purity and identity confirmation.
Frequently Asked Questions
What purity do I need for my research?▼
≥95% is adequate for most research applications including cell assays and binding studies. For quantitative experiments, dose-response studies, or sensitive assays, ≥98% is recommended to minimize interference from impurities.
Does higher purity always mean better quality?▼
For research purposes, yes — higher purity means fewer unknown impurities that could affect results. However, the practical difference between 98% and 99.5% may be negligible for many assay types. The critical threshold is usually ≥95% for reliable research-grade work.
All products are for Laboratory Research Use Only.
Not for human consumption, veterinary use, or diagnostic purposes.