Phosphate Buffer Chart

1 M K-Phosphate, pH 7.0

300 ml of 1 M KH2PO4, 700 ml 1M K2HPO4, the pH is 7.0 measured using a pH meter.

Stock solution A

2 M monobasic sodium phosphate, monohydrate (276 g/L), NaH₂PO₄

Stock solution B

2 M dibasic sodium phosphate (284 g/L). Na₂HPO₄

Filter thru 0.45 u filter

Make 0.2 M: Dilute 10 times. (100 ml  +  900 ml water), filter thru 0.45 u filter

Mixing an appropriate volume (ml) of  A and  B as shown in the table below and diluting to a total volume of 200 ml, to make a 0.1 M phosphate buffer of the required pH at room temperature.

0.2 M NaH2PO4	0.2 M Na2HPO4	pH
92.0	8.0	5.8
90.0	10.0	5.9
87.7	12.3	6.0
85.5	15.0	6.1
81.5	19.5	6.2
77.5	22.5	6.3
73.5	26.5	6.4
68.5	31.5	6.5
62.5	37.5	6.6
56.5	43.5	6.7
51.0	49.0	6.8
45.0	55.0	6.9
39.0	61.0	7.0
33.0	67.0	7.1
28.0	72.0	7.2
23.0	77.0	7.3
19.0	81.0	7.4
16.0	84.0	7.5
13.0	87.0	7.6
10.5	89.5	7.7
8.5	91.5	7.8
7.0	93	7.9
5.3	94.7	8.0

Potassium Phosphate Monobasic Anhydrous--Sodium Phosphate Dibasic Heptahydrate

Potassium  Phosphate Monobasic Anhydrous,  KH2PO4, g/L	Sodium Phosphate Dibasic Heptahydrate, Na2HPO4·7H2O g/L	23 °C pH		Potassium Phosphate Monobasic Anhydrous, KH2PO4, g/L	Sodium Phosphate Dibasic Heptahydrate Na2HPO4·7H2O, g/L	23 °C pH
22.4	3.49	5.7		10.80	29.51	6.9
22.08	4.29	5.8		9.36	32.73	7.0
21.60	5.37	5.9		7.92	35.95	7.1
21.05	6.60	6.0		6.72	38.63	7.2
20.40	8.05	6.1		5.52	41.31	7.3
19.56	9.93	6.2		4.56	43.46	7.4
18.60	12.07	6.3		3.84	45.07	7.5
17.64	14.22	6.4		3.12	46.68	7.6
16.44	16.90	6.5		2.52	48.55	7.7
15.00	20.12	6.6		2.04	49.09	7.8
13.56	23.34	6.7		1.68	49.89	7.9
12.24	26.29	6.8		1.27	50.81	8.0

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

Na2HPO4 • 2H2O, M. wt. 178.05; 0.2M-solution contains 35.61 g/l.
Na2HPO4 • 12H2O, M. wt. 358.22; 0.2M -solution contains 71.64 g/l.
NaH2PO4 • H2O, M. wt. 138.01;  0.2M-solution contains 27.6 g/l.
NaH2PO4 • 2H2O, M. wt. 156.03; 0.2M-solution contains 31.21 g/l.

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

pH, 25 °C	x ml 0.2M-Na2HPO4	y ml 0.2M-NaH2PO2
5.8	4.0	46.0
6.0	6.15	43.85
6.2	9.25	40.75
6.4	13.25	36.75
6.6	18.75	31.25
6.8	24.5	25.5
7.0	30.5	19.5
7.2	36.0	14.0
7.4	40.5	9.5
7.6	43.5	6.5
7.8	45.75	4.25
8.0	47.35	2.65

Yet Another Protocol
1 M sodium phosphate buffer (pH 6.0-7.2)

Mixing 1 M NaH2PO4 (monobasic) and 1 M Na2HPO4 (dibasic) stock solutions in the volumes designated in the table below results in 1 L of 1 M sodium phosphate buffer of the desired pH.

To prepare the stock solutions:

Dissolve 138 g of Na2HPO4•H2O (monobasic; m.w. = 138 g) in sufficient H2O to make a final volume of 1 L

Dissolve 142 g of Na2HPO4 (dibasic; m.w. = 142 g) in sufficient H2O to make a final volume of 1 L.

pH	Volume (mL) of 1 M Na2HPO4	Volume (mL) of 1 M NaH2PO4
5.8	7.9	92.1
6	12	88
6.2	17.8	88.2
6.4	25.5	74.5
6.6	35.2	64.8
6.8	46.3	53.7
7	57.7	42.3
7.2	68.4	31.6
7.4	77.4	22.6
7.6	84.5	15.5
7.8	89.6	10.4
8	93.2	6.8

0.1 M sodium phosphate buffer (pH 7.4)

Add 3.1 g of NaH2PO4•H2O and 10.9 g of Na2HPO4 (anhydrous) to distilled H2O to make a volume of 1 L. The pH of the final solution will be 7.4. This buffer can be stored for up to 1 mo at 4°C.

0.1 M sodium phosphate buffer (from 1 M stocks) at 25°C

To prepare 1 L of 0.1 M sodium phosphate buffer of the desired pH, the following mixtures should be diluted to 1 L (final volume) with H2O.

pH	Volume (mL) of 1 M Na2HPO4	Volume (mL) of 1 M NaH2PO4
5.8	7.9	92.1
6	12	88
6.2	17.8	88.2
6.4	25.5	74.5
6.6	35.2	64.8
6.8	46.3	53.7
7	57.7	42.3
7.2	68.4	31.6
7.4	77.4	22.6
7.6	84.5	15.5
7.8	89.6	10.4
8	93.2	6.8

0.2 M KH2PO4	0.2 M K2HPO4	(to 200ml) pH
91.5	8.5	5.8
86.8	13.2	6.0
80.8	19.2	6.2
72.2	27.8	6.4
61.9	38.1	6.6
50.3	49.7	6.8
38.5	61.5	7.0
28.3	71.7	7.2
19.8	80.2	7.4
13.4	86.6	7.6
9.2	90.8	7.8
6.0	94.0	8.0