Key takeaways
- Peptide synthesis and purification use organic solvents that can leave traces.
- Headspace gas chromatography (GC) is the standard method for residual solvents.
- USP <467> and ICH Q3C group solvents into classes with reference limits.
- Results are reported in parts per million (ppm).
Solid-phase peptide synthesis and HPLC purification use solvents such as DMF, dichloromethane, acetonitrile and diethyl ether. Lyophilization removes most of them, but traces can remain in the final powder.
How headspace GC works
A weighed sample is sealed in a vial and heated. Volatile solvents move into the gas above the sample (the headspace). A portion of that gas is injected into a gas chromatograph, which separates the solvents, and a detector measures each one against reference standards.
Solvent classes
| Class | Description | Examples |
|---|---|---|
| Class 1 | Solvents to be avoided | Benzene, carbon tetrachloride |
| Class 2 | Solvents to be limited | Acetonitrile, dichloromethane, DMF, methanol |
| Class 3 | Solvents with lower toxic potential | Acetone, ethanol, ethyl acetate |
The reference limits in USP <467> and ICH Q3C were written for pharmaceutical products. Research suppliers often use them as a benchmark for reporting.
Reading a residual solvent report
- Check which solvents were tested; a report covers only the solvents in its method.
- Results are in ppm, compared with a stated limit for each solvent.
- The method, the laboratory and the test date should be named.
Frequently asked questions
Why does acetonitrile often appear on reports?
It is the main organic solvent in reversed-phase HPLC purification.
Can lyophilization remove all solvents?
It removes most volatile solvents, but traces can remain. Testing confirms the level.
Why might residual solvent data be missing for a lot?
Not every lot is tested for every attribute. Ask the supplier for the lot number.
Disclaimer. This article is for research and educational purposes only. It describes laboratory and analytical practice and is not medical advice. It contains no dosing, administration or human-use guidance. Veridryx products are sold for laboratory research use only and are not for human or veterinary use.
References
- USP General Chapter <467> Residual Solvents. United States Pharmacopeia.
- ICH Q3C Impurities: Guideline for Residual Solvents. International Council for Harmonisation.