GB/T 6920-1986: Water quality. Determination of pH value. Glass electrode method

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Scope

1.1 This method is applicable to the determination of the pH value of drinking water, surface
water and industrial wastewater.
1.2 The color, turbidity, colloidal substance, oxidizing agent, reducing agent and high
salinity of water do not interfere with the determination; however, in the strong acidic
solution with pH < 1, there is so-called "acid error", which can be determined according to
the acidity; in the alkaline solution with pH >10, due to the existence of a large amount of
sodium ions, the error is generated; therefore, the reading is relatively low, which is
commonly referred to as "sodium error". For the methods of eliminating the "sodium error",
in addition to use the specially-made electrode of “low sodium error”, it can also adopt the
standard buffer solution which is similar to the pH value of the solution under test, in order
to calibrate the instrument.
The temperature can affect the electric potential of the electrodes and the ionization
balance of the water. It shall be noted that the compensation device of the adjusting
instrument should be consistent with the temperature of the solution, and the temperature
error of the standard buffer solution between the sample to be measured and the calibrating
instrument should be within ± 1°C.
2 Definitions 1
The pH is defined from the operation. For solution X, it should measure the galvanic cell’s.
reference electrode｜KCl concentrated solution｜｜ solution X |H2| Pt
electromotive force EX. Replace the solution X, whose pH(X) is unknown, into the standard
1 This definition is cited from p.151 of GB 3100-3102-82 Quantities and units.
pH solution S, and measure the battery’s electromotive force ES, then,
pH(X)＝pH (S) + (Es - Ex) F / (RTln10)
Therefore, the defined pH is the dimensionless quantity.
pH has no theoretical significance. the definition is the practical definition. However, within
the limited range of the dilute aqueous solution whose amount-of-substance concentration
is less than 0.1mol·dm3, when it is neither strong acidity nor the strong alkalinity (2 < pH <
12), then it has the followings according to the definition.
pH＝-log10[c(H＋)y / (mol·dm3)] ± 0.02
In the formula, c(H+) represents the amount-of-substance concentration of the hydrogen
ion (H+). y represents the activity coefficient of the typical 1-1-valence electrolyte in the
solution.

Basic Data

Standard ID	GB/T 6920-1986 (GB/T6920-1986)
Description (Translated English)	Water quality. Determination of pH value. Glass electrode method
Sector / Industry	National Standard (Recommended)
Classification of Chinese Standard	Z50
Classification of International Standard	13.06
Word Count Estimation	6,679
Date of Issue	10/10/1986
Date of Implementation	3/1/1987
Issuing agency(ies)	National Environmental Protection Agency
Summary	This standard applies to the determination of drinking water, surface water and industrial wastewater pH.