If your laboratory asks you to buy a “heavy peptide,” it is easy to focus on the sequence and miss the label. Two quotes can describe the same amino-acid sequence but offer different materials. The labeling position, amount and supporting measurements all matter.
Here is a simple way to read the request and prepare a clearer inquiry.
1. What makes a peptide “heavy”?
A peptide is a short chain of amino acids. In a stable isotope labeled peptide, selected atoms are replaced with heavier isotopes of the same element, such as carbon-13 or nitrogen-15. The matching form with natural isotope abundances is called the light peptide.
“Heavy” describes the isotope label. It does not mean a longer chain, a larger vial or a higher chemical purity.
JPT describes carbon and nitrogen labeling and offers separately quantified peptide formats. Its descriptions are useful background; they are not specifications for NHD products.
2. Why do laboratories use a matching heavy peptide?
A mass spectrometer measures ions by their mass-to-charge ratio. A suitable heavy peptide gives the laboratory a distinguishable reference signal alongside the matching light peptide. Researchers often call this reference an internal standard.
The AQUA method uses isotope-labeled peptide internal standards to measure selected peptides. Buying a standard is only part of the work: the laboratory still needs a suitable, validated measurement method.
Source: the AQUA research protocol
3. Write the label position, not just “heavy”
For example, lysine labeled with six carbon-13 atoms and two nitrogen-15 atoms has an approximate mass increase of 8 Da. Arginine with six carbon-13 atoms and four nitrogen-15 atoms gives approximately 10 Da. These are rounded mass differences for the stated labels, not a batch test result.
In your request, identify the amino acid and its position in the sequence. A sequence containing two lysines needs more detail than “label the lysine.” Also specify the ends of the chain and any other modifications.
Ask the laboratory to confirm the required label notation and expected mass difference before the order is approved.
4. Three numbers that should stay separate
Isotopic enrichment describes the isotope composition of the labeled material. Chemical purity describes the result of a specified purity test. Assigned peptide amount or concentration tells you how much material has been determined on a stated basis. One high percentage does not answer all three questions.
If you need an internal standard for quantitative work, ask how its amount was assigned, which uncertainty or tolerance is reported, and whether that information applies to the batch offered.
Understand peptide purity versus content
5. What published measurements show
Salek and colleagues examined 113 heavy peptides in a 2022 study. In their mixtures, about half showed light-to-heavy signal ratios above 100 ppm (0.01%). These were instrument signal ratios under that study’s conditions, not powder mass fractions or a market-wide defect rate.
The buying question is practical: is relevant information about the matching light peptide available, and will your laboratory check for it in appropriate controls? High isotopic enrichment alone is not a complete answer.
Read the study and its measurement limits
6. A short checklist for your inquiry
Send the exact sequence and label position; isotope notation; terminal groups and other modifications; required amount per vial; dry or solution format; purity and identity records; and any assigned-content or light-contamination information your laboratory requires.
Explain when the standard will enter the workflow. A peptide added after digestion cannot establish how completely a protein was digested earlier. This timing question should be agreed with the laboratory running the assay.
For packing only, five vials containing 2 nmol each total 10 nmol. This original arithmetic example is not a recommended experimental amount or an NHD specification. The amount basis and labeling requirements still need agreement.
7. Send NHD the exact request
Start with the custom peptide inquiry route and attach the laboratory’s specification. NHD needs to confirm whether the requested label, quantity and documents can be supplied before quoting. This article does not establish a dedicated isotope-standard service or guaranteed availability.
View NHD’s custom peptide synthesis page
Send your sequence and label requirements
If you need a named catalog material instead, use the product directory. A standard catalog listing does not establish that a stable-isotope-labeled version is available.
For laboratory research procurement only. The examples are not NHD batch results, clinical-use guidance or dosing instructions.
Sources & editorial method
AI-assisted writing checked against the listed sources.
1 linked records are listed in the references below. Read the editorial and AI-assistance policy.
How to interpret this article
Published measurements describe the cited study; calculations are examples, not NHD batch results.
Research-use boundary: Catalog materials discussed on this website are for laboratory research, development and manufacturing use only, not for human or veterinary use. This content is not medical advice and does not provide administration instructions.
Primary records and authoritative sources
- Quantitative ProteomicsQuantitative Proteomics
Continue with structured records
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