Reference Solution must always be calibrated for the pH meter before measuring pH.

Reference (standard) solution must always be calibrated for the pH meter before measuring pH. A buffer solution whose pH is unlikely to vary is used as the reference solution. Without a reliable reference solution, erroneous results can be expected.

Next, we will present five types of reference solutions specified in JIS, and the pH values of these solutions at each temperature.
Although it is not difficult to make these reference solutions, the process is troublesome if you do not have equipment for the purpose. It is more economical to purchase commercially available solutions.

Standard pH of Reference Solution, by Temperature
(JIS Z 8802 confirmed in 2011)

Temp(.C)
	Nitrate Salt	Phthalate	Reference Solution Neutral Phosphate	Borate	Carbonate
0	1.67	4.01	6.98	9.46	10.32
5	1.67	4.01	6.95	9.39	(10.25)
10	1.67	4.00	6.92	9.33	10.18
15	1.67	4.00	6.90	9.27	(10.12)
20	1.68	4.00	6.88	9.22	(10.07)
25	1.68	4.01	6.86	9.18	10.02
30	1.69	4.01	6.85	9.14	(9.97)
35	1.69	4.02	6.84	9.10	(9.93)
38	---	---	---	---	9.91
40	1.70	4.03	6.84	9.07	---
45	1.70	4.04	6.83	9.04	---
50	1.71	4.06	6.83	9.01	---
55	1.72	4.08	6.84	8.99	---
60	1.73	4.10	6.84	8.96	---
70	1.74	4.12	6.85	8.93	---
80	1.77	4.16	6.86	8.89	---
90	1.80	4.20	6.88	8.85	---
95	1.81	4.23	6.89	8.83	---

Names and Composition of Reference Solutions

Name	Composition
Oxalate reference solution	0.05 mol/L potassium tetraoxalate KH3 (C2O4) 2·2H2O solution
Phthalate reference solution	0.05 mol/L potassium hydrogenphthalate C6H4(COOK)(COOH)solution
Neutral phosphate reference solution	0.025 mol/L monopotassium phosphate KH2 PO4- 0.025 mol/L dibasic sodium phosphate Na2HPO4 solution
Borate reference solution	0.01 mol/L sodium borate (borax) Na2B4O7·10H2O solution
Carbonate reference solution	0.025 mol/L sodium bicarbonate NaHCO3- 0.025 mol/L sodium carbonate Na2CO3 solution