Buffer Selector
Enter a target pH. The tool lists the buffer systems that hold there, ranked by how close their pKa sits to your pH, with the base-to-acid mixing ratio from Henderson-Hasselbalch.
How to use this tool
Pick the right buffer for the pH you need to hold. Enter your target pH and the tool shortlists buffer systems that work there and tells you how to mix each one.
What to enter
- Target pH: the pH you want to maintain, 0–14. A buffer works best when its pKa is close to this value.
- Match window (± pKa units): how far from your pH a buffer's pKa may sit and still be listed. The default 1.0 matches the practical pKa ± 1 buffering range; widen it to see more candidates.
Reading the result
You get the best-match buffer (pKa nearest your pH) plus a ranked table. The base-to-acid ratio is how much conjugate base to acid you mix; a ratio near 1:1 (pH ≈ pKa) gives the strongest, most symmetric buffering.
Worked example
For pH 7.40 (blood) the tool lists the systems within ±1.0, phosphate (pKa₂ ≈ 7.2) and HEPES (≈ 7.5) among them, each with the base-to-acid ratio that lands exactly on 7.40.
Target
Suitable buffers
Buffers are ranked by how close their pKa sits to your pH; the top one buffers most strongly and resists drift best. The base-to-acid ratio is how much conjugate base to acid you mix, a ratio near 1:1 (pH ≈ pKa) gives the highest capacity, while a lopsided ratio still hits the pH but with less to spare on one side.
Methodology
A buffer resists pH change best when its pKa is near the target pH; the practical range is pKa ± 1. The tool scans common systems and keeps those whose (any) pKa is within your match window, sorted by the absolute distance |pH − pKa|.
The mixing ratio is the Henderson-Hasselbalch result: [base]/[acid] = 10(pH − pKa). A ratio near 1 (pH ≈ pKa) gives the strongest buffering.
Sources
- pKa values at 25 °C from the CRC Handbook; zwitterionic "Good's" buffers from Good et al. (1966).
Known limits
- pKa is temperature- and ionic-strength-dependent; tabulated values are 25 °C, dilute.
- The list covers common lab buffers, not an exhaustive catalogue.