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Merck

Buffer Reference Center

Choosing the Right Biological Buffer

Choose a buffer based on your pH requirements as well as the pKa, a measure of acid strength that accounts for pH, concentration, and temperature. Regulatory or purity needs for your exact application should also be considered. The following tables can help you navigate preparation of many common buffer solutions by pH and pKa.

In addition to the tables below, we've developed several buffer recipe calculators to assist your buffer preparation.

TBE and TAE for gel electrophoresis have slightly more involved recipes. We can help you pick the right one.

What are buffer grades?

Buffer grade indicates the quality and impurity levels appropriate for different uses. We provide six grades of buffers indicated for general lab use, final pharmaceutical formulation and manufacturing, and applications in between that may need trace metal testing or materials of a specified purity.

Useful pH Ranges of Selected Biological Buffers Chart (25 °C, 0.1 M)

BuffersUseful pH RangepKa
(at 20 °C)
pKa
(at 25 °C)
pKa
(at 37 °C)
Reagent GradeBioPerformance Certified Grade
MES5.5–6.76.166.105.97M8250M2933
Bis-Tris5.8–7.2n/a6.506.36B9754B4429
ADA6.0–7.26.656.596.46A9883n/a
ACES6.1–7.56.886.786.54A9758A3594
PIPES6.1–7.56.806.766.66P6757P1851
MOPSO6.2–7.6n/a6.906.75M8389n/a
Bis-Tris Propane6.3–9.5n/a6.8, 9.0n/aB6755B4679
BES6.4–7.87.177.096.90B9879B4554
MOPS6.5–7.97.287.207.02M1254M3183
TES6.8–8.27.507.407.16T1375T5691
HEPES6.8–8.27.557.487.31H3375H4034
DIPSO7.0–8.2n/a7.607.35n/an/a
MOBS6.9–8.3n/a7.60n/aM3295n/a
TAPSO7.0–8.2n/a7.607.39T9269n/a
Tris or Trizma®7.0–9.08.208.067.72T1503T6066
HEPPSO7.1–8.5n/a7.806.66n/an/a
POPSO7.2–8.5n/a7.807.63P3405n/a
TEA7.3–8.3n/a7.80n/an/an/a
EPPS7.3–8.7n/a8.00n/aE9502E0276
Tricine7.4–8.88.168.057.80T0377T5816
Gly-Gly7.5–8.9n/a8.20n/aG1002G3915
Bicine7.6–9.08.358.268.04B3876n/a
HEPBS7.6–9.0n/a8.30n/aH6903n/a
TAPS7.7-9.18.498.408.18T5130T5316
AMPD7.8–9.7n/a8.80n/aA9754n/a
TABS8.2–9.6n/a8.90n/an/an/a
AMPSO8.3–9.7n/a9.009.10A6659n/a
CHES8.6–10.09.559.499.36C2885n/a
CAPSO8.9–10.3n/a9.609.43C2278n/a
AMP9.0–10.5n/a9.70n/an/an/a
CAPS9.7–11.110.5610.4010.02C2632n/a
CABS10.0–11.4n/a10.70n/aC5580n/a

Tris or Trizma® Buffer Preparation Table – pH vs. Temperature

pH at Temperature
5 °C25 °C37 °C
7.767.206.91
7.897.307.02
7.977.407.12
8.077.507.22
8.187.607.30
8.267.707.40
8.377.807.52
8.487.907.62
8.588.007.71
8.688.107.80
8.788.207.91
8.888.308.01
8.988.408.10
9.098.508.22
9.188.608.31
9.288.708.42
9.368.808.51
9.478.908.62
9.569.008.70
g/L for 0.05 M Solution
Trizma® HCLTrizma® Base
7.020.67
6.850.80
6.610.97
6.351.18
6.061.39
5.721.66
5.321.97
4.882.30
4.442.65
4.022.97
3.543.34
3.073.70
2.644.03
2.214.36
1.834.65
1.504.90
1.235.13
0.965.32
0.765.47

Phosphate Buffer Preparation Table – 0.2 M solution

Potassium
Phosphate Monobasic Anhydrous g/L
Sodium Phosphate Dibasic Heptahydrate g/L23 °C pH
22.43.495.7
22.084.295.8
21.605.375.9
21.056.606.0
20.408.056.1
19.569.936.2
18.6012.076.3
17.6414.226.4
16.4416.906.5
15.0020.126.6
13.5623.346.7
12.2426.296.8
Potassium Phosphate Monobasic
Anhydrous g/L
Sodium Phosphate
Dibasic Heptahydrate g/L
23 °C pH
10.8029.516.9
9.3632.737.0
7.9235.957.1
6.7238.637.2
5.5241.317.3
4.5643.467.4
3.8445.077.5
3.1246.687.6
2.5248.557.7
2.0449.097.8
1.6849.897.9
1.2750.818.0

Citric Acid – Na2HPO4 Buffer Preparation, pH 2.6–7.61

Citric acid monohydrate, C6H8O7 • H2O, MW 210.14; 0.1 M contains 21.01 g/L. Na2HPO4, MW 141.98; 0.2 M contains 28.40 g/L, or Na2HPO4 • 2H2O, MW 178.05; 0.2 M contains 35.61 g/L.

x mL 0.1 M-citric acid and y mL 0.2 M-Na2HPO4 mixed

pHx mL 0.1 M-citric acidy mL 0.2-Na2HPO4
2.689.1010.90
2.884.1515.85
3.079.4520.55
3.275.3024.70
3.471.5028.50
3.667.8032.20
3.864.5035.50
4.061.4538.55
4.258.6041.40
4.455.9044.10
4.653.2546.75
4.850.7049.30
5.048.5051.50
5.246.4053.60
5.444.2555.75
5.642.0058.00
5.839.5560.45
6.036.8563.15
6.233.9066.10
6.430.7569.25
6.627.2572.75
6.822.7577.25
7.017.6582.35
7.213.0586.95
7.49.1590.85
7.66.3593.65

Citric Acid – Sodium Citrate Buffer Preparation, pH 3.0-6.21

Citric acid monohydrate, C6H8O7 • H2O, MW 210.14; 0.1 M contains 21.01 g/L. Trisodium citrate dihydrate, C6H5O7Na3 • 2H2O, MW 294.12; 0.1 M contains 29.41 g/L.

x mL 0.1 M-citric acid and y mL 0.1 M-trisodium citrate mixed

pHx mL 0.1 M-citric acidy mL 0.1 M-trisodium citrate
3.082.018.0
3.277.522.5
3.473.027.0
3.668.531.5
3.863.536.5
4.059.041.0
4.254.046.0
4.449.550.5
4.644.555.5
4.840.060.0
5.035.065.0
5.230.569.5
5.425.574.5
5.621.079.0
5.816.084.0
6.011.588.5
6.28.092.0

Sodium Acetate – Acetic Acid Buffer PREPARATION, pH 3.7–5.61

Sodium acetate trihydrate, CH3COONa • 3H2O, MW 136.09; 0.2 M contains 27.22 g/L.

x mL 0.2 M-NaOAc and y mL 0.2 M-HOAc mixed

pH, 18 °Cx mL 0.2 M-NaOAcy mL 0.2 M-HOAc
3.710.090.0
3.812.088.0
4.018.082.0
4.226.573.5
4.437.063.0
4.649.051.0
4.859.041.0
5.070.030.0
5.279.021.0
5.486.014.0
5.691.09.0

Na2HPO4 – NaH2PO4 Buffer PREPARATION, pH 5.8-8.0 at 25 °C1

Na2HPO4 • 2H2O, MW 178.05; 0.2 M contains 35.61 g/L. Na2HPO4 • 12H2O, MW 358.22; 0.2 M contains 71.64 g/L. NaH2PO4 • H2O, MW 138.01; 0.2 M contains 27.6 g/L. NaH2PO4 • 2H2O, MW 156.03; 0.2 M contains 31.21 g/L.

x mL 0.2 M-Na2HPO4, y mL 0.2 M-NaH2PO4; diluted to 100 mL with H2O

pH, 25 °Cx mL 0.2 M-Na2HPO4y mL 0.2 M-NaH2PO4
5.84.046.0
6.06.1543.85
6.29.2540.75
6.413.2536.75
6.618.7531.25
6.824.525.5
7.030.519.5
7.236.014.0
7.440.59.5
7.643.56.5
7.845.754.25
8.047.352.65

Imidazole (glyoxaline) – HCl Buffer PREPARATION, pH 6.2–7.8 at 25 °C1

Imidazole, C3H4N2, MW 68.08

25 mL 0.2 M-imidazole (13.62 g/L), x mL 0.2 M-HCl, diluted to 100 mL with H2O

pH, 25 °Cx mL 0.2 M-HCl
6.221.45
6.419.9
6.617.75
6.815.2
7.012.15
7.29.3
7.46.8
7.64.65
7.83.0

Sodium Carbonate – Sodium Bicarbonate Buffer PREPARATION, pH 9.2-10.81

Na2CO3 • 10H2O, MW 286.2; 0.1 M contains 28.62 g/L. NaHCO3, MW 84.0; 0.1 M contains 8.40 g/L.

x mL 0.1 M-Na2CO3 and y mL 0.1 M-Na2HCO3 mixed

20 °C37 °C
x mL 0.1 M-Na2CO3y mL 0.1 M-Na2HCO3
9.28.81090
9.49.12080
9.59.43070
9.89.54060
9.99.75050
10.19.96040
10.310.17030
10.510.38020
10.810.69010

Buffer Preparation Formulas and Equations

Percentage by weight (w/v)

(% buffer desired / 100) × final buffer volume (mL) = g of starting material needed.

Molar Solutions

desired molarity × formula weight × solution final volume (L) = grams needed

Henderson-Hasselbach Equation

Henderson ph

Reference

1.
Dawson R, Elliot D, Elliot W, Jones KM. 1986. Data for Biochemical Research. 3rd ed.. Oxford Science Publ..
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