Questions deserve straight answers.
No marketing fluff, no evasion. Clear, honest answers to the most common questions about research peptides — from synthesis and purity to storage and handling.
General peptide questions
What are peptides and how are they made?
Peptides are short chains of amino acids, typically between 2 and 50 residues, joined by peptide bonds. They are widely used in pharmaceutical research, immunology, cell biology, and drug discovery.
Research-grade peptides are produced via solid-phase peptide synthesis (SPPS). Amino acids are added one at a time to a growing chain on a resin support. Once the full sequence is assembled, the peptide is cleaved from the resin, purified by reverse-phase HPLC, and freeze-dried into a stable powder.
Do some peptides contain mannitol?
Yes. Mannitol is a sugar alcohol used as a bulking agent during freeze-drying. It helps keep the peptide stable during lyophilisation and produces a more visible, uniform cake in the vial. Mannitol is inert and does not affect peptide purity or interfere with research assays.
What is the shelf life of lyophilised peptides?
Lyophilised, refrigerated (2-8°C): Typically stable for 24 months or longer
Lyophilised, frozen (-20°C): Extended stability, often over 36 months
Reconstituted: Varies by peptide and solvent — most should be aliquoted and stored frozen
Peptides prone to oxidation (those containing methionine or cysteine) may have a shorter shelf life.
Quality assurance and testing
What is a Certificate of Analysis (CoA)?
A CoA confirms the identity and minimum purity of a peptide based on HPLC and mass spectrometry testing. A typical CoA includes peptide identity (sequence, molecular formula, molecular weight), purity percentage, mass spectrometry confirmation, physical appearance, and batch/lot number.
What are common impurities in peptide synthesis?
Even high-quality synthesis produces trace impurities:
Deletion sequences: Missing one or more amino acids from the target sequence
Truncated sequences: Shorter fragments from premature chain termination
Oxidised forms: Common in peptides containing methionine or cysteine
Deamidation products: Asparagine and glutamine converting to aspartic/glutamic acid
Racemisation: L-amino acids converting to D-amino acids at certain positions
Residual solvents: Trace TFA, acetonitrile, or scavengers from purification
Products at 98%+ purity mean impurities account for less than 2% of total material.
What is net peptide content?
Net peptide content (NPC) is the actual mass of active peptide in a vial, as opposed to the total mass. Total mass includes residual moisture (3-8%), counter-ions (TFA or acetate salts), and any excipients like mannitol.
For example, a vial labelled "5mg BPC-157" with 75% NPC contains approximately 3.75mg of active peptide. NPC matters when calculating molar concentrations for research.
What is the difference between purity and yield?
Purity is the proportion of the target peptide relative to all peptide-related species, measured by HPLC. Yield is the total mass obtained from a synthesis run. Purity is the quality metric that matters for research — a 98% purity means 98% is the correct sequence.
Storage and handling best practices
Temperature control
Store at 2-8°C (fridge) for short-term use or -20°C (freezer) for long-term storage. Let vials reach room temperature before opening.
Light protection
Keep away from direct light. UV degrades certain residues, particularly tryptophan and tyrosine.
Moisture control
Keep vials sealed until ready for use. Freeze-dried peptides absorb moisture from air, accelerating degradation.
After reconstitution
Aliquot into single-use volumes if possible and store frozen. Avoid repeated freeze-thaw cycles.
Common issues explained
Why does my vial appear nearly empty?
5mg is a very small amount — roughly a few grains of fine salt. In a standard 2-3ml vial, it will look like a thin film, a small disc, or barely visible powder at the bottom. This is completely normal.
Weighing the vial is not reliable for verification — most lab balances have a margin of error that can exceed the total peptide mass, and vial tare weights vary between units.
What if my reconstituted peptide looks cloudy?
Common causes include incomplete dissolution (gentle swirling usually resolves this), pH mismatch (try a different solvent), too-high concentration, or mannitol dissolving. If cloudiness persists after gentle mixing at room temperature, do not use the solution — it may indicate aggregation or degradation.
Can I pre-blend multiple peptides?
It's generally better to keep peptides as individual, single-compound solutions. Blending makes it harder to verify purity, identity, and quantity of each component. If you need multiple peptides for a study, reconstitute each separately and manage combination according to your own protocols.
Frequently asked questions
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