- HPLC measures how pure a peptide is; LC-MS confirms it is the right molecule. A good certificate of analysis (COA) reports both for the specific batch.
- "99 % purity" is not the same as "99 % peptide": the powder also contains counterions (TFA or acetate) and some water, which is what net peptide content measures.
- Most research peptides ship lyophilized (freeze-dried) because the dry powder is far more stable than a solution.
- In biology, the key words are receptor, agonist and half-life: they explain why tirzepatide acts on two receptors and why a DAC stretches CJC-1295's half-life to about a week.
- Evidence levels matter: in vitro (cells) and in vivo (animals) findings come before Phase 1-3 human trials and regulatory approval.
Analysis and quality
HPLC (high-performance liquid chromatography)
A separation technique that pushes a dissolved sample through a packed column under high pressure. Different molecules leave the column at different times, and a UV detector draws each as a peak. For peptides, HPLC is the standard way to measure purity: the main peak's share of the total peak area is the purity figure on a COA. We explain the method in depth in our HPLC vs LC-MS article.
LC-MS (liquid chromatography-mass spectrometry)
HPLC coupled to a mass spectrometer. The chromatography separates the components and the mass spectrometer weighs each one. LC-MS is the standard identity test: if the measured mass matches the theoretical molar mass of the sequence, the peptide is what the label says. HPLC tells you how much of the main component there is; LC-MS tells you what it is.
Purity
The percentage of the HPLC signal that belongs to the target peptide, usually measured by UV absorbance at around 214-220 nm, where the peptide bond absorbs. "≥99 % HPLC" means impurities make up 1 % or less of the peak area. It does not describe water or salt content. Our article on what 99 % purity really means covers the fine print.
Impurity
Anything in the sample that is not the target molecule. In synthetic peptides the typical impurities are deletion sequences (one amino acid missing), truncated chains, incompletely deprotected residues and oxidised forms. They are chemically very close to the target, which is why a high-resolution HPLC method matters.
Net peptide content
The share of the powder's total weight that is actually peptide, as opposed to counterions and residual moisture. A vial can be ≥99 % pure by HPLC and still have a net peptide content well below 100 %, because salts and water are invisible to UV purity analysis. It is measured by amino acid analysis or elemental nitrogen analysis.
Retention time
The time a compound takes to travel through the HPLC column to the detector under a given method. Under the same conditions a given peptide always elutes at the same retention time, so it helps identify the main peak and spot shifts between batches.
m/z (mass-to-charge ratio)
What a mass spectrometer actually measures. Peptides often carry several charges at once, so one molecule can appear as a series of peaks (for example [M+2H]2+ and [M+3H]3+). Software deconvolutes these into a single molecular mass that is compared with the theoretical value.
COA (certificate of analysis)
The batch-specific document that reports what a product was tested for and the results: identity (LC-MS), purity (HPLC), appearance and batch number, sometimes also water or endotoxin content. A COA is only meaningful if its batch number matches the vial. Cryopept publishes the COA from its internal batch test protocol on each product page.
Endotoxin
Lipopolysaccharide from the outer membrane of Gram-negative bacteria, one of the most potent triggers of inflammation known. Endotoxin can survive sterilisation, so it is tested separately, classically with the LAL (Limulus amebocyte lysate) assay or its recombinant factor C alternative, and reported in endotoxin units (EU). It matters for cell and animal work because even trace amounts can skew immune readouts.
Chemistry and handling
Amino acid
The building block of peptides and proteins. Twenty standard amino acids are coded by genes; each has a common backbone and a different side chain that gives it its properties (charged, greasy, small, bulky). Peptide chemists also use non-natural ones, such as Aib in semaglutide and tirzepatide, to block enzymatic breakdown.
Amino acid sequence
The order of amino acids in a chain, written from the N-terminus to the C-terminus, usually in one-letter code. BPC-157, for example, is GEPPPGKPADDAGLV: 15 residues. The sequence determines the peptide's identity, and a single swapped residue makes a different molecule.
Peptide bond
The amide bond (-CO-NH-) that links the carboxyl group of one amino acid to the amino group of the next, releasing a water molecule. Chains of roughly 2-50 amino acids are usually called peptides; longer chains are proteins. Enzymes called proteases cut peptide bonds, which is the main reason unmodified peptides are short-lived in the body.
Residue
An amino acid once it is incorporated into a chain (it has lost the atoms of water in forming the peptide bond). "A 29-residue peptide" such as CJC-1295 without DAC simply means 29 amino acids long.
Molar mass (molecular weight)
The mass of one mole of a molecule, in g/mol (or daltons for a single molecule). It is calculated from the formula and is the number LC-MS results are checked against: BPC-157 is about 1419.5 g/mol, the tripeptide KPV about 342.4 g/mol.
SPPS (solid-phase peptide synthesis)
The method used to make almost all research peptides, introduced by Bruce Merrifield in 1963. The chain is built one amino acid at a time on insoluble resin beads, then cleaved off, usually with trifluoroacetic acid, and purified by preparative HPLC.
TFA salt
Trifluoroacetic acid is used to cleave peptides from the resin and as an HPLC mobile-phase additive, so a freshly purified peptide usually ends up as a trifluoroacetate salt, with TFA ions paired to its basic residues. TFA is a normal part of the product, but because it can affect some sensitive cell assays, many labs prefer an acetate form.
Acetate salt
The same peptide with acetate instead of TFA as the counterion, obtained by an extra ion-exchange step. Acetate is the counterion most often used for peptide medicines. The FDA's 2026 compounding review listed each peptide as both "free base" and "acetate" for exactly this reason.
Free base
The peptide molecule on its own, without a counterion. Molar mass and formula on a product page usually refer to the free base; the salt form adds the weight of the counterions.
Lyophilization (freeze-drying)
Removing water from a frozen solution by sublimation under vacuum, leaving a dry "cake" or powder. Lyophilized peptides are far more stable than solutions because hydrolysis, oxidation and microbial growth all need water. See our article on storing lyophilised peptides for temperature and light guidance.
BAC water (bacteriostatic water)
Sterile water containing 0.9 % benzyl alcohol as a preservative that stops bacteria from multiplying. Laboratories use it as the diluent for lyophilized peptides when a vial will be accessed more than once; plain sterile water has no preservative and is meant for single use.
Lipidation (acylation)
Attaching a fatty acid chain to a peptide so that it binds albumin in the blood. This is the main trick behind modern once-weekly peptides: semaglutide, tirzepatide and retatrutide all carry a fatty diacid side chain that protects them from clearance.
Biology and pharmacology
Receptor
A protein, usually on the cell surface, that recognises a specific signalling molecule and triggers a response inside the cell. Most peptide hormones act on receptors; knowing the receptor is the first step to understanding what a peptide does.
GPCR (G protein-coupled receptor)
The largest family of cell-surface receptors, with seven segments crossing the membrane. GLP-1, GIP, glucagon, GHRH and melanocortin receptors are all GPCRs, which is why so many research peptides share similar signalling (often via cAMP).
Agonist
A molecule that binds a receptor and activates it. A dual agonist (tirzepatide: GIP and GLP-1) or triple agonist (retatrutide: GIP, GLP-1 and glucagon) activates several receptors with one molecule.
Incretin
A gut hormone released after eating that boosts insulin secretion in a glucose-dependent way. The two known incretins are GLP-1 and GIP, and together they account for much of the extra insulin released after an oral glucose load compared with the same glucose given intravenously.
GLP-1 (glucagon-like peptide-1)
An incretin made by L-cells in the gut. It stimulates insulin, suppresses glucagon, slows gastric emptying and signals fullness in the brain. Native GLP-1 has a half-life of only about 2 minutes, so drugs such as semaglutide and tirzepatide are engineered analogues. Our GLP-1 guide covers the class.
GIP (glucose-dependent insulinotropic polypeptide)
The second incretin, secreted by K-cells in the upper small intestine. GIP receptor activity is what tirzepatide and retatrutide add on top of GLP-1, and it is an active area of metabolic research.
DPP-4 (dipeptidyl peptidase-4)
The enzyme that inactivates GLP-1 and GIP by clipping off their first two amino acids. DPP-4 is why native incretins last only minutes. Incretin-based peptides place a non-natural residue such as Aib at position 2 to resist it, and DPP-4 inhibitor tablets (gliptins) work by blocking the enzyme.
Half-life
The time it takes for the concentration of a compound to fall by half. Native peptides often last minutes; engineering can stretch this to days. Tirzepatide's label half-life is about 5 days, and CJC-1295 with DAC about 6-8 days in humans.
DAC (Drug Affinity Complex)
A lysine-linked maleimide group added to CJC-1295 that binds covalently to albumin in the blood, extending the half-life to about a week. CJC-1295 without DAC (Modified GRF 1-29) lacks this group and acts for a much shorter time, which is the version Cryopept supplies. Our DAC vs no-DAC comparison explains the difference.
Bioavailability
The fraction of a compound that reaches the circulation intact. Most peptides have very low oral bioavailability because stomach acid and proteases break them down; BPC-157 is a studied exception because of its stability in gastric juice.
Research and regulation
In vitro
Latin for "in glass": experiments in cells, tissues or test tubes outside a living organism. In vitro results show mechanism but not whether an effect happens in a whole body.
In vivo
Experiments in a living organism, usually rodents in peptide research. Animal results are a stronger signal than cells but do not reliably predict effects in humans.
Preclinical
All research before first testing in humans: in vitro, in vivo, toxicology and pharmacokinetics. Many research peptides, including BPC-157, still have mostly preclinical evidence.
Phase 1 trial
The first test in humans, typically 20-100 healthy volunteers or patients, mainly to study safety, tolerability and how the body handles the compound.
Phase 2 trial
A trial in up to several hundred people with the target condition, to get early evidence of efficacy and to explore further safety and dose-response.
Phase 3 trial
Large trials, usually 300 to 3,000 or more participants, that confirm efficacy and monitor adverse events. Positive Phase 3 results are the basis for a marketing application. Retatrutide's TRIUMPH programme is a current example.
Marketing authorisation (approval)
Permission from a regulator (FDA in the US; EMA and the European Commission, or national agencies, in the EU) to sell a specific finished medicine for a specific use. It applies to that product, not to the molecule in general.
Compounding (503A)
Pharmacy preparation of a medicine for an individual prescription. In the US, section 503A of the FD&C Act limits which bulk substances may be used; in 2026 an FDA advisory committee voted to recommend adding BPC-157, KPV, TB-500 and other peptides to that list. See our FDA peptide review 2026 article.
RUO (research use only)
A label meaning the product is supplied for laboratory research and is not a medicine, food or cosmetic. RUO material is characterised by analytical data (identity, purity, batch COA), not by therapeutic claims.
Definitions are for scientific education. Cryopept Labs products are for laboratory research use only - not for human or veterinary use.
