Why Purity Grades Exist
Not all research applications require the same level of peptide purity. A preliminary screening assay testing dozens of peptides may not need 99% purity for each, while a quantitative binding study absolutely does. Understanding purity grades helps researchers balance cost, quality, and experimental requirements.
Crude Peptides (~50-75% purity)
Crude peptides are the direct output of solid-phase peptide synthesis after cleavage from the resin but before any purification. They contain the target peptide along with truncated sequences, deletion peptides, protecting group remnants, and residual reagents. Crude peptides are the least expensive option and are sometimes used for initial screening or antibody production where high purity is not critical.
Desalted Peptides (~75-85% purity)
Desalting removes salts, small molecule impurities, and residual solvents from the crude peptide through a simple filtration or extraction step. This improves purity modestly but does not remove peptide-based impurities like truncated sequences. Desalted peptides are a cost-effective option for applications where the primary concern is removing non-peptide contaminants.
HPLC-Purified Peptides (>95% to >99%)
HPLC purification uses reverse-phase chromatography to separate the target peptide from all impurities based on hydrophobicity differences. This is the gold standard for research-grade peptides. Within HPLC-purified grades, further distinctions exist based on the final purity achieved after purification — typically >95%, >98%, or >99%.
For quantitative research — dose-response studies, receptor binding assays, cell-based functional assays — HPLC-purified peptides at >98% purity are the minimum standard. For the highest confidence in your results, >99% purity is recommended.
How to Verify the Grade
Always request a Certificate of Analysis that includes the HPLC chromatogram. The purity percentage should be calculated from the chromatogram's peak areas, not estimated or assumed. A supplier selling "HPLC-purified" peptides should be able to provide batch-specific analytical data demonstrating the actual purity achieved.
