Guides to peptide quality and handling
How purity, identity and storage are specified and documented. Written for laboratory buyers, and limited to chemistry.
- What a certificate of analysis tells you (and what it doesn't)
How to read a peptide certificate of analysis: the tests it usually lists, what each one establishes, and the limits of a single lot document.
- HPLC purity explained: what a peptide purity figure means
How reversed-phase HPLC measures peptide purity, how to read a chromatogram, and why a purity percentage depends on the method behind it.
- Mass spectrometry and peptide identity confirmation
How mass spectrometry confirms a peptide's identity: monoisotopic and average mass, charge states, and what a matching mass does and does not prove.
- Net peptide content vs purity: what is actually in the vial
Why HPLC purity and net peptide content are different measurements, what makes up the rest of a lyophilised powder, and how the two are measured.
- How to store lyophilised peptides
Storage conditions for freeze-dried peptides: temperature, moisture, light and oxygen, why each matters, and how to handle a vial that has been in the cold.
- Shelf life and stability of lyophilised peptides
How long freeze-dried peptides stay intact: the degradation pathways, how stability is studied, and why a shelf life is a property of a lot and its storage.
- Why lyophilised vials look nearly empty: cake, bulking agents and fill weights
A few milligrams of freeze-dried peptide occupies very little volume. How a lyophilised cake forms, what bulking agents like mannitol do, and what a fill weight means.
- Bacteriostatic water vs sterile water: laboratory solvent chemistry
What separates bacteriostatic water from sterile water as laboratory solvents: composition, the role of benzyl alcohol, sterility, and chemical compatibility.
- Dilute acetic acid as a solvent for basic peptides
Why dilute acetic acid dissolves basic peptides that resist neutral water: net charge, isoelectric point, pKa, and the practical limits of the approach.
- How solid-phase peptide synthesis works, and why TFA salts are common
A plain-language outline of Fmoc solid-phase peptide synthesis, where trifluoroacetate counter-ions come from, and why the salt form affects a peptide powder.
- Checking a certificate of analysis: how to verify a lot document
Practical checks for a peptide certificate of analysis: matching the lot, reading the raw data, checking the sign-off, and spotting reused or edited documents.
- Peptide solubility: choosing a solvent from the sequence
How to predict whether a peptide will dissolve in water, dilute acid, dilute base or an organic co-solvent, using net charge and hydrophobicity from the sequence.
- C-terminal amides and N-terminal acetylation
What the -NH2 and Ac- in a peptide sequence mean: how terminal modifications change charge, mass and solubility, how they are made in synthesis, and how to check them on a COA.
- Reading impurity peaks: what +16, +1 and −18 Da mean
How common peptide impurities show up on HPLC and mass spectrometry: oxidation, deamidation, aspartimide, deletion sequences and leftover protecting groups, with their mass shifts.
- Amino acid codes and how to read a peptide sequence
The one- and three-letter codes for the 20 standard amino acids, with residue masses, plus the notation for terminal groups, D-amino acids, non-standard residues and fragments.
- Isoelectric point and net charge: how they are calculated
How a peptide's net charge and isoelectric point (pI) are estimated from its sequence using pKa values and the Henderson–Hasselbalch equation, with worked examples and their limits.
- Measuring peptide concentration: UV absorbance and other methods
How the concentration of a peptide solution is measured: absorbance at 280 nm and 205 nm, amino acid analysis, and why common protein assays are unreliable for short peptides.
- GHK-Cu: the chemistry of a peptide–copper complex
The structure and chemistry of GHK-Cu, the copper(II) complex of glycyl-histidyl-lysine: how copper is bound, why the powder is blue, how pH affects the complex, and how it is identified.
- NAD+: structure, stability and handling of a coenzyme
The chemistry of NAD+ (nicotinamide adenine dinucleotide): its structure, why it is not a peptide, how it degrades in acid and alkali, how it is measured by UV absorbance, and how to store it.
- Looking up a compound: CAS numbers, PubChem and the literature
How to identify a research compound reliably using CAS registry numbers, PubChem, UniProt and PubMed, including how to validate a CAS number and why salts and complexes have their own entries.
- What is a peptide? Bonds, length and naming
A chemical introduction to peptides: how amino acids join through peptide bonds, how peptides differ from proteins, the backbone and side chains, and how peptides are named.
- Thymosin β4 and its fragments: nomenclature and structure
What the names thymosin β4, Tβ4(17–23), Ac-SDKP and TB-500 refer to: sequences, residue numbering, formulas and masses, and how to tell which molecule a document describes.
- The 20 amino acids: structures, side chains and properties
The general structure of an amino acid, the zwitterion form, L and D stereochemistry, and the 20 standard amino acids grouped by side chain with their pKa values.
- How chromatography works: from paper strips to columns
What chromatography is, how the stationary and mobile phases separate a mixture, how to calculate Rf values, and the main types from paper to HPLC.
- How HPLC works: separation, retention time and what it can't tell you
What HPLC stands for, how the instrument separates compounds, what retention time means, and what an HPLC test can and cannot tell you about a peptide.
- Beyond HPLC and MS: NMR, FTIR, amino acid analysis and peptide mapping
What NMR spectroscopy, FTIR, amino acid analysis, elemental analysis and peptide mapping measure in a peptide sample, their limits, and when labs use them.
- How peptides are ionised for mass spec: LC-MS, electrospray and MALDI-TOF
How electrospray ionisation and MALDI turn peptides into gas-phase ions, how LC-MS links each HPLC peak to a mass, and how TOF analysers separate ions.
- Hygroscopic powders: why lyophilised peptides absorb moisture and how to handle vials
What hygroscopic means, why freeze-dried peptides and NAD+ take up water from the air, what moisture does to a powder, and how to open, weigh and reseal vials.
- What lyophilisation is: freeze-drying, the cake and excipients
Lyophilisation removes water from a frozen solution by sublimation under vacuum. The three stages, collapse temperature, the cake, excipients and residual moisture.
- Trifluoroacetic acid (TFA) in peptides: counter-ions and salt exchange
What trifluoroacetic acid is, why trifluoroacetate stays on synthetic peptides, how much it weighs, and how it is measured and exchanged for acetate or chloride.
- Water content and Karl Fischer titration: why a peptide COA reports it
How Karl Fischer titration measures water, volumetric vs coulometric methods, the oven technique, and how water content fits into net peptide content.
- Lot numbers and batch numbers: tracing a vial to its COA
What a lot or batch number is, how it differs from a SKU or expiry date, and how to use it to match a peptide vial to its certificate of analysis.
- Peptide purity testing in the UK: what labs offer and what it costs
What an analytical lab can test on a peptide sample, how to send one, what drives the cost, and how ISO/IEC 17025 and UKAS accreditation show a COA is credible.
- How to choose a UK research peptide supplier: what to check before you order
A checklist for assessing a UK research peptide supplier: company details, lot-matched COAs with raw data, chemistry data, storage, payment and red flags.
- Why research vials are borosilicate glass: glass types, stoppers and crimp seals
What borosilicate glass is, how Type I, II and III glass differ, and how stoppers and crimp seals close a vial of lyophilised peptide.
- Are peptides legal in the UK? Research peptides and the law
How UK law treats synthetic peptides sold as laboratory reagents: the Human Medicines Regulations 2012, the MHRA, research-use-only labelling and controlled drugs.
- CJC-1295 with and without DAC: what the modification is
What DAC means in CJC-1295: the maleimidopropionyl-lysine added to modified GRF (1-29), with sequences, formulas, masses, CAS numbers and how MS tells them apart.
- Endotoxin: what it is and why reagent specifications list it
What endotoxin (lipopolysaccharide) is, how it differs from exotoxin, why it confounds cell-based assays, and how LAL and recombinant factor C tests measure it.
- Molarity, mg/mL and dilutions: the maths of laboratory solutions
The formulas behind laboratory solutions: moles, molarity, mass from molarity, mg/mL and % w/v, C1V1 = C2V2 and serial dilutions, with worked buffer and salt examples.
Unfamiliar term? See the glossary.