What does heavy metals testing on a peptide COA show?

Heavy metals is the older, informal name. The current term is elemental impurities, meaning trace elements in a material that are not part of the intended molecule. USP replaced its older General Chapter <231> Heavy Metals with <232> Elemental Impurities—Limits and <233> Elemental Impurities—Procedures, and USP set January 1, 2018 as the date <232> became applicable to drug product monographs. The ICH Q3D guideline, published by FDA, is the international framework behind those chapters.

Q3D covers finished medicines, and its scope explicitly includes products containing synthetically produced polypeptides. Research peptides are not medicines and Q3D limits are not specifications for them, but Q3D is still the clearest public explanation of which elements matter and why, so most labs that test peptides for metals borrow its element lists.

ICH Q3D names the usual sources. Some elements are residual catalysts or inorganic reagents added on purpose during synthesis. Others are present in starting materials or water without being added. Some come from processing equipment, and some can leach from container and closure systems over time.

Peptide synthesis uses large volumes of solvents, resins, coupling reagents and acids, and the crude product passes through pumps, columns and steel or glass vessels before it is freeze-dried into a vial. Each step is a possible, usually small, source of trace elements. A metals test on the finished lot is the only way to see the combined result, because none of the other common COA tests measure elements at all.

The sample is usually digested in acid so the organic peptide is destroyed and the elements are left in solution. The solution is then measured by an element-specific technique. ICH Q3D says the test should be specific for each element identified for control, using pharmacopoeial procedures or suitable validated alternatives.

A 2026 review in Critical Reviews in Analytical Chemistry compares the main options. Atomic absorption spectrometry is low-cost and sensitive but measures one element at a time. ICP-OES is robust and measures many elements at once, which suits routine quality control. ICP-MS has the highest sensitivity, down to nanograms per liter, at a higher cost. X-ray fluorescence is fast and non-destructive, but the review describes it as a screening tool with limits for quantification. That is why a metals result reported as not detected by a screening method carries much less weight than an ICP-MS result with a stated detection limit.

Five checks that use only what is printed on the report.

1. Check which elements were measured: a heavy-metals result covers only the elements listed, so note whether arsenic, cadmium, lead and mercury are all there.
2. Check the technique: ICP-MS or ICP-OES measures each element separately; a screening method such as XRF cannot confirm low concentrations.
3. Read each result with its unit and limit: a value such as < 0.2 ppm means below the reporting limit; not detected means nothing without the detection limit beside it.
4. Find out what the acceptance limit is: an internal screening limit set by the lab is different from a published specification, and the report should say which applies.
5. Match the report to the lot and the lab: the lot number, sample description and the lab's accreditation scope for the metals method should all line up.

Some research peptides contain a metal by design. GHK-Cu is a copper complex of the tripeptide glycyl-histidyl-lysine, so copper is part of the compound, not an impurity in it. A copper result on a GHK-Cu report measures the intended copper, and only the other elements on the panel say anything about contamination. Reading a copper peptide report with a generic heavy-metals mindset would flag the wrong thing.

An elemental impurities panel says nothing about whether the vial contains the right peptide, how pure it is, or how much of it there is. Those questions are answered by LC-MS identity, HPLC purity and a quantity or net peptide content result. It also does not cover endotoxin, residual solvents or water, which have their own methods. Our guides to synthetic peptide impurities and to endotoxin testing cover those.

Vitality Chems' published lot reports are HPLC reports; they do not include an elemental impurity panel. We publish exactly what each report shows on the testing page and the lot lookup and do not describe tests that were not run.

This page describes analytical chemistry for in-vitro laboratory research use only. It makes no claim about elemental impurity levels in any particular lot, and the ICH and USP documents it cites are background references, not specifications that apply to research materials.