Heavy metals testing

Heavy metals testing measures toxic elements such as lead, cadmium, mercury and arsenic in a sample, today usually by inductively coupled plasma mass spectrometry (ICP-MS).

Metals can reach a synthetic peptide from reagents, catalysts and water, and from the equipment it touches during manufacture. The four checked most often are lead, cadmium, mercury and arsenic. ICH Q3D, the international guideline on elemental impurities, puts them in its highest-concern class because they are toxic and can be present without anyone adding them.

ICP-MS passes the dissolved sample through an argon plasma hot enough to break it into individual charged atoms, then sorts the atoms by mass and counts each element, down to parts per billion. It replaced an older colorimetric test, USP <231>, which gave one combined figure for the metals that form colored sulfides. USP retired that test in favor of USP <232> and <233>, which name each element and its limit. A certificate that reports "heavy metals" without naming a method or the elements may be using the older approach.

Two cautions apply when reading the figure. An element that is part of the compound is not an impurity: GHK-Cu contains copper by design, so a copper reading there is expected. And a pass means only that each element was below the limit the laboratory applied, which a full certificate states alongside it.

Related terms

• Mass spectrometry
• Certificate of analysis
• Microbial limits testing

UPDATED OCTOBER 30, 2026 · REVIEWED BY DEL POTTER, PHD