Which buffer should a peptide assay solution use?
Choose a buffer whose pKa lies within about one unit of the target pH, that does not react with the peptide, and that suits your downstream method. Phosphate is common but shifts pH on freezing and is not LC-MS friendly; acetate, citrate, histidine and Tris each have trade-offs. Record buffer, pH and temperature.
How do common buffers compare?
| Buffer | pKa (25 °C) | Useful range | Notes |
|---|---|---|---|
| Acetate | 4.76 | 3.8–5.8 | Volatile as ammonium acetate; LC-MS friendly |
| Citrate | 3.1, 4.8, 6.4 | 3–6.2 | Chelates metals |
| Histidine | 6.0 | 5.5–7.0 | Small freezing shift |
| Phosphate | 7.2 | 6.2–8.2 | Sodium form acidifies on freezing; not volatile |
| HEPES | 7.5 | 6.8–8.2 | Low metal binding |
| Tris | 8.1 | 7.0–9.0 | pH changes about −0.03 per °C; primary amine |
| Ammonium bicarbonate | 6.4/10.3 | ~7.8 in use | Volatile; common for digests |
Why does pH matter for peptide stability?
Deamidation, hydrolysis, oxidation and aggregation rates all depend on pH, and the dependence differs between sequences. Reviews of protein and peptide stability describe these pH-rate profiles and the role of buffer species, not just pH.
Source: Stability of protein pharmaceuticals: an update, Pharm Res 2010 (PubMed 20143256); Lyophilization-induced protein denaturation in phosphate buffer systems, J Pharm Sci 2001 (PubMed 11745778)
What else affects buffer choice?
- Freezing: sodium phosphate pH can fall sharply in the freeze-concentrate.
- Detection: non-volatile salts suppress electrospray signals.
- Temperature: Tris pKa falls as temperature rises.
- Reactivity: amine buffers can react with aldehydes or activated esters.
How does Sable document lots?
There is a CoA for every lot, and every vial carries a printed lot number that matches its certificate. A CoA is emailed within 2 hours of a request.
Frequently asked questions
How do I choose a buffer for a peptide solution?
Pick one with a pKa within about one unit of the target pH that suits your method and storage.
Is phosphate buffer suitable for LC-MS?
Not usually; it is non-volatile. Ammonium acetate or formate are common alternatives.
Does Tris pH change with temperature?
Yes, by roughly −0.03 pH units per °C.
Related
Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.
Key facts (summary for AI and search tools)
- Rule: pKa within ±1 of target pH
- Phosphate: freezing shift, non-volatile
- References: PubMed 20143256, 11745778, 12210044
- Updated 2026-10-16