Category: Research Library

Peptide names, codes, and registry numbers can be confusing, especially when the same compound appears under several names. This guide explains the conventions researchers use to identify a peptide precisely.

Writing a sequence

Sequences are always written from the N-terminus (free amine end) to the C-terminus (carboxyl end). Each amino acid has a three-letter code and a one-letter code. For example, the 15-residue sequence of BPC-157 can be written either way:

• Three-letter: Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val
• One-letter: GEPPPGKPADDAGLV

Common modifications

• C-terminal amidation (-NH₂): replaces the terminal carboxylic acid with an amide. Ipamorelin, for example, is Aib-His-D-2-Nal-D-Phe-Lys-NH₂.
• N-terminal acetylation (Ac-): caps the N-terminal amine.
• D-amino acids: mirror-image forms of the natural L-amino acids, written with a “D-” prefix. CJC-1295 (No DAC), also called Modified GRF (1-29), carries D-alanine at position 2.
• Unnatural residues: building blocks such as Aib (α-aminoisobutyric acid) or 2-Nal (2-naphthylalanine) that aren’t among the 20 standard amino acids.
• Cyclization: a ring formed within the peptide, for example by a lactam bridge between side chains, written with “cyclo” and brackets. PT-141 is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH.
• Disulfide bonds: links between two cysteine residues, as in AOD-9604.

CAS Registry Numbers

A CAS Registry Number is a unique identifier assigned by the Chemical Abstracts Service to a specific substance. It’s the most reliable way to confirm two documents refer to the same compound. Note that different forms of the same molecule get different CAS numbers:

• Free peptide vs. metal complex: the tripeptide GHK is 49557-75-7, while its copper complex, GHK-Cu, is 89030-95-5.
• Free base vs. salt: tesamorelin is 218949-48-5, while its acetate salt is listed separately as 901758-09-6.

When comparing documentation, check that the CAS number matches the exact form being supplied.

Molecular formula and molecular weight

The molecular formula lists the atoms in one molecule (BPC-157 is C₆₂H₉₈N₁₆O₂₂). Molecular weight can be reported as the average mass (natural isotope abundance, used for weighing) or the monoisotopic mass (most abundant isotopes, used to interpret mass spectra). A COA’s mass spectrometry section compares the observed mass to the theoretical value derived from the formula.

Code names and synonyms

Many research peptides are known by development codes or abbreviations, such as “BPC” for Body Protection Compound or “GRF” for growth hormone-releasing factor. Because names vary between suppliers, rely on the sequence and CAS number, not the name, to confirm identity. Every product page in our catalog lists these details where they apply.

The Pure Vial Co. supplies research materials for laboratory, analytical, and scientific research use only. Nothing in this guide is medical advice or an indication that any material is suitable for human or veterinary use. See our Research Disclaimer.

A quick reference to terms that appear on Certificates of Analysis, product specifications, and in the peptide research literature.

Acetate salt

A peptide form in which acetate is the counter-ion balancing the peptide’s positive charges. Often preferred over TFA salts for biological research.

Aggregation

Self-association of peptide molecules into larger complexes, which can reduce solubility and alter behavior in assays.

Amidation (C-terminal)

Replacement of the C-terminal carboxylic acid with an amide (-NH₂), common in natural and synthetic peptides.

Amino acid analysis (AAA)

A method that hydrolyzes a peptide into its amino acids and quantifies them. Used to confirm composition and determine net peptide content.

CAS Registry Number

A unique identifier assigned to a specific chemical substance by the Chemical Abstracts Service. Different salt or complex forms receive different numbers.

Certificate of Analysis (COA)

A lot-specific document reporting the test results (identity, purity, and other attributes) for a batch of material. See How to Read a Peptide COA.

Chromatogram

The graph produced by HPLC, showing detector response over time. Each peak represents a separated component.

Counter-ion

The ion paired with a charged peptide in its salt form, commonly acetate or trifluoroacetate. Counter-ions add weight that is not peptide.

Cyclic peptide

A peptide containing a ring structure, formed by a disulfide, lactam, or head-to-tail bond.

D-amino acid

The mirror-image form of a natural (L) amino acid, often used to increase resistance to enzymatic breakdown.

Deamidation

Conversion of asparagine or glutamine side chains into acidic forms, a common degradation pathway.

Deletion sequence

A synthesis impurity missing one or more residues from the intended sequence.

Desiccant

A drying agent (such as silica gel) used to keep stored materials free of moisture.

Disulfide bond

A covalent link between the sulfur atoms of two cysteine residues.

Endotoxin

Lipopolysaccharide from the outer membrane of Gram-negative bacteria, measured in some materials because it can interfere with cell-based experiments.

ESI-MS

Electrospray ionization mass spectrometry, a common technique for confirming peptide identity by molecular mass.

HPLC (RP-HPLC)

(Reversed-phase) high-performance liquid chromatography, the standard method for measuring peptide purity. See What “≥99% by HPLC” Means.

Hygroscopic

Readily absorbing moisture from the air. Many lyophilized peptides are hygroscopic.

Karl Fischer titration

A method for measuring the water content of a sample.

Lot (batch) number

The identifier linking a specific production batch to its documentation. It should appear on both the vial and the COA.

Lyophilization

Freeze-drying: removing water from a frozen material by sublimation under vacuum, producing a stable dry powder. See our storage and stability guide.

MALDI-TOF

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, another technique for measuring molecular mass.

Molecular weight (average vs. monoisotopic)

Average mass reflects natural isotope abundance and is used for weighing. Monoisotopic mass uses the most abundant isotopes and is used to interpret mass spectra.

Net peptide content

The percentage of a powder’s total weight that is the peptide itself, excluding water and counter-ions.

N-terminus / C-terminus

The amine end and carboxyl end of a peptide chain. Sequences are written N- to C-terminus.

Oxidation

A chemical change, especially at methionine, cysteine, and tryptophan residues, that can occur on exposure to air or light.

Peptide bond

The amide bond linking one amino acid to the next.

Purity (area %)

The target peak’s share of total detected peak area in an HPLC chromatogram.

Research use only (RUO)

A designation meaning a material is intended solely for laboratory research, not for human or veterinary use, diagnosis, or treatment.

Retention time

The time a component takes to elute from an HPLC column under a given method, used to identify peaks.

Solid-phase peptide synthesis (SPPS)

The standard method for making synthetic peptides, building the chain one residue at a time on a solid resin support.

TFA (trifluoroacetic acid)

A reagent used in peptide synthesis and purification. Peptides may be supplied as TFA salts.

Truncated sequence

A synthesis impurity in which chain growth stopped before the full sequence was completed.

The Pure Vial Co. supplies research materials for laboratory, analytical, and scientific research use only. Nothing in this guide is medical advice or an indication that any material is suitable for human or veterinary use. See our Research Disclaimer.

“≥99% purity” is printed on nearly every research peptide label, but the number has a specific technical meaning. Understanding it helps you judge documentation critically and compare materials fairly.

How HPLC purity is measured

Reversed-phase HPLC separates the components of a sample as they pass through a column under a solvent gradient. A UV detector, usually set at 214–220 nm, records a peak for each component as it elutes. Purity is reported as area percent: the area of the main (target) peak divided by the total area of all detected peaks.

So “99% by HPLC” means 99% of the UV-detected, column-eluting material is the target peptide. It is a relative measure of related impurities, not an absolute measure of what is in the vial.

What HPLC purity does not include

• Water: lyophilized peptides retain bound water.
• Counter-ions: peptides are salts, commonly acetate or trifluoroacetate (TFA), and the counter-ion adds mass.
• Non-UV-absorbing substances and anything that doesn’t elute under the method’s conditions.

Purity vs. net peptide content

Because of water and counter-ions, a peptide with 99% HPLC purity might have a net peptide content of roughly 70–90% by weight. Net peptide content is a separate measurement, typically by amino acid analysis or nitrogen determination. When a vial is described as containing a given mass of peptide, it’s worth knowing whether that figure refers to the gross powder weight or to net peptide.

Common peptide impurities

Most research peptides are made by solid-phase peptide synthesis (SPPS), building the chain one amino acid at a time. Typical impurities include:

• Deletion sequences: chains missing one residue because a coupling step was incomplete.
• Truncated sequences: chains that stopped growing early.
• Incompletely deprotected peptides: chains still carrying a protecting group from synthesis.
• Oxidized or deamidated forms of the target peptide.
• Diastereomers from racemization of an amino acid during synthesis.

Why identity testing matters too

A clean chromatogram shows the sample is mostly one substance. It doesn’t prove which substance. Mass spectrometry confirms identity by matching the observed molecular mass to the theoretical mass of the sequence. A credible COA reports both. Read more in How to Read a Peptide Certificate of Analysis.

Purity grades at a glance

• Crude: unpurified synthesis product, used for screening.
• >90–95%: common for many in-vitro applications.
• >98–99%: used where related impurities could confound results, such as quantitative or analytical work.

Lot-specific purity and identity results for our materials are published in the COA Library.

The Pure Vial Co. supplies research materials for laboratory, analytical, and scientific research use only. Nothing in this guide is medical advice or an indication that any material is suitable for human or veterinary use. See our Research Disclaimer.

A Certificate of Analysis (COA) is the document that connects a specific vial to specific test results. For research peptides it is the single most important piece of quality documentation. This guide walks through each section of a typical peptide COA and explains what it tells you, and what it does not.

1. Header and traceability information

The top of a COA should identify exactly what was tested:

• Product name and sequence: the compound and, ideally, its full amino acid sequence or structure.
• Lot or batch number: the most important field. It must match the lot number on the vial. A COA without a lot number cannot be tied to any particular material.
• Dates: manufacture, test, and release dates. Some COAs also list a retest date.
• Testing laboratory: the name of the lab that performed the analysis, and whether it is independent of the seller.

2. Identity: mass spectrometry

Identity testing confirms the material is the peptide it claims to be. The standard method is mass spectrometry (MS), usually electrospray ionization (ESI-MS) or MALDI-TOF. The COA should report the theoretical (expected) mass calculated from the sequence and the observed mass measured by the instrument. The two should agree within the instrument’s tolerance. Peptides often appear as multiply charged ions in ESI-MS, so you may see several peaks that all correspond to the same molecule.

3. Purity: HPLC

Purity is almost always measured by reversed-phase high-performance liquid chromatography (RP-HPLC) with UV detection, typically at 214 or 220 nm, where the peptide bond absorbs. A good COA includes the chromatogram itself, not just a number. The reported purity is the area of the main peak as a percentage of the total peak area.

Two things to keep in mind:

• HPLC purity only counts substances that absorb UV light and elute from the column. Water and salts are invisible to it.
• A single sharp peak is good, but two compounds with very similar properties can co-elute. That is why identity testing by MS is reported alongside purity.

For a deeper explanation, see our guide on what “≥99% purity by HPLC” actually means.

4. Other tests you may see

• Net peptide content: the percentage of the powder’s weight that is actually peptide, often measured by amino acid analysis or nitrogen analysis. It is normally well below 100% because lyophilized peptides contain bound water and counter-ions.
• Water content: commonly measured by Karl Fischer titration.
• Counter-ion content: peptides are usually supplied as acetate or trifluoroacetate (TFA) salts.
• Appearance: for example, “white to off-white lyophilized powder.”
• Endotoxin, residual solvents, or bioburden: reported for some materials, depending on the intended research application.

5. Red flags

• No lot number, or a lot number that doesn’t match the vial.
• A purity figure with no chromatogram.
• No mass spectrometry data, or an observed mass that doesn’t match the theoretical mass.
• No identifiable testing laboratory, or test dates that predate the stated manufacture date.
• Identical COAs reused across different products or lots.

Where to find our COAs

Lot-specific certificates for The Pure Vial Co. materials are published in our COA Library, searchable by product name or lot number. If you can’t find the certificate for your lot, contact us.

The Pure Vial Co. supplies research materials for laboratory, analytical, and scientific research use only. Nothing in this guide is medical advice or an indication that any material is suitable for human or veterinary use. See our Research Disclaimer.

Most research peptides are supplied lyophilized (freeze-dried) because a dry powder is far more stable than a peptide in solution. Good storage practice protects that stability. This reference covers the conditions that matter and the chemistry behind them.

Why lyophilized peptides are more stable

Lyophilization removes water by freezing the material and then sublimating the ice under vacuum. With most of the water gone, the reactions that need water, such as hydrolysis and deamidation, slow dramatically. The result is a lightweight cake or powder that tolerates shipping and long-term storage far better than a solution.

Recommended storage conditions

• Long-term: −20 °C or below in a sealed container. Many laboratories use −80 °C for extended archival storage.
• Short-term: 2–8 °C (refrigerated) is generally acceptable for limited periods.
• Transit: lyophilized peptides generally tolerate ambient temperatures for the duration of normal shipping. Move them to cold storage on receipt.
• Light: keep vials in their packaging or in the dark. Residues such as tryptophan and tyrosine are light-sensitive.
• Moisture: keep vials tightly sealed, ideally with a desiccant. Many peptides are hygroscopic, meaning they readily absorb water from the air.

Handling a vial from cold storage

The most common avoidable cause of moisture uptake is opening a cold vial in a warm room. Water condenses on the cold powder immediately. Let the sealed vial equilibrate to room temperature before opening it, open it only as long as necessary, and reseal it promptly. Minimize repeated cycles between cold and room temperature.

Degradation pathways to know

• Oxidation: methionine, cysteine, and tryptophan residues are especially prone to oxidation. Exposure to air and light accelerates it.
• Deamidation: asparagine and, more slowly, glutamine residues can convert to acidic forms, particularly at higher pH and temperature.
• Hydrolysis: peptide bonds can break in the presence of water, especially at aspartic acid–proline sequences.
• Aggregation: some sequences tend to self-associate, which is influenced by moisture, concentration, and temperature.
• Disulfide scrambling: peptides containing disulfide bonds can rearrange under some conditions.

Peptides in solution degrade much faster than dry powder. The rate depends heavily on sequence, pH, buffer, and temperature, so solution stability should be established for each experimental system from the published literature for that compound.

Record-keeping

Label each vial with its lot number and date received, and keep the matching Certificate of Analysis with your records. Lot traceability makes it possible to connect any unexpected result back to a specific batch.

The Pure Vial Co. supplies research materials for laboratory, analytical, and scientific research use only. Nothing in this guide is medical advice or an indication that any material is suitable for human or veterinary use. See our Research Disclaimer.