GB/T 23769-2009 English PDF (GBT23769-2009)

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GB/T 23769-2009: Inorganic chemical products -- General method for the determination of pH values
GB/T 23769-2009
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 71.060.01
G 10
GB 23769-2009
Inorganic Chemical Products - General
Method for the Determination of pH Values
ISSUED ON: MAY 13, 2009
IMPLEMENTED ON: JANUARY 01, 2010
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative References ... 4
3 Principle ... 4
4 Safety Tips ... 5
5 General Provisions ... 5
6 Reagents ... 5
7 Apparatus ... 7
8 Analysis Procedures ... 7
Appendix A (Informative) Precautions for Electrode Use ... 9
Inorganic Chemical Products - General
Method for the Determination of pH Values
1 Scope
This Standard specifies the principles, safety tips, general provisions, reagents,
apparatus, and analytical procedures for the determination of the pH value of aqueous
solutions of inorganic chemical products by the potentiometric method.
This Standard is applicable to the determination of the pH value of aqueous solutions
of inorganic chemical products. The measurement range of pH value is 1~12.
2 Normative References
The provisions in following documents become the provisions of this Standard through
reference in this Standard. For dated references, the subsequent amendments
(excluding corrigendum) or revisions do not apply to this Standard, however, parties
who reach an agreement based on this Standard are encouraged to study if the latest
versions of these documents are applicable. For undated references, the latest edition
of the referenced document applies.
GB/T 6682-2008 Water for Analytical Laboratory Use – Specification and Test
Methods (ISO 3696:1987, MOD)
HG/T 3696.1 Inorganic Chemicals for Industrial Use - Preparations of Standard
and Reagent Solutions for Chemical Analysis - Part 1: Preparations of Standard
Volumetric Solutions
HG/T 3696.3 Inorganic Chemicals for Industrial Use - Preparations of Standard
and Reagent Solutions for Chemical Analysis - Part 3: Preparations of Reagent
Solutions
3 Principle
Immerse the specified indicator electrode and reference electrode or composite
electrode in the same test solution to form a primary cell whose electromotive force is
related to the pH value of the solution. The pH value of the solution may be obtained
by measuring the electromotive force of the primary cell.
7 Apparatus
7.1 Electrode (see Appendix A for the use of electrodes):
7.1.1 Indicator electrode: glass electrode;
7.1.2 Reference electrode: calomel electrode;
7.1.3 Composite electrode.
7.2 Acidity meter: the graduation value is 0.02.
8 Analysis Procedures
8.1 Preparation of test solution
Prepare the sample into a test solution with certain concentration by the carbon
dioxide-free water according to the requirements of the product standard.
8.2 Calibration of acidity meter
Prepare two standard buffer solutions at the same time; so that the pH value of one
standard buffer solution is greater than and close to the pH value of the test solution,
and the other standard buffer solution is less than and close to the pH value of the test
solution. Calibrate the pH meter by the above two standard buffer solutions. Adjust the
temperature compensation knob to the temperature of the standard buffer solution;
and refer to the pH value of the standard buffer solution at this temperature. Use two
standard buffer solutions to calibrate respectively; the calibration error shall be no
greater than 0.1 (if greater than 0.1, the electrode needs to be cleaned or replaced).
Use a standard buffer solution whose pH value is close to that of the sample test
solution to position.
8.3 Determination
Rinse the electrode with water; then wash with the test solution; adjust the temperature
of the test solution to 25°C±1°C; and adjust the temperature compensation knob of the
acid meter to 25°C. Insert the electrode into the test solution; add a stir bar; under
stirring state (or according to the specific requirements of the product standard),
determine the pH value of the test solution; and the measured pH value shall be stable
for at least 1min. Divide the solution into 2 portions and measure them respectively.
The difference between the two measured pH values shall be no greater than ±0.02.
Avoid acid or alkaline gas intrusion during operation.
Take the arithmetic average of the parallel determination results as the determination
Appendix A
(Informative)
Precautions for Electrode Use
A.1 Glass electrode
Soak the temporarily-unused glass electrodes in water, and change the water
frequently. The glass electrode that has not been used for a long period of time shall
be stored in a dry place; and it needs to be immersed in water for 24h in advance to
activate it before use.
When measuring the pH value, all the bulbs of the glass electrode shall be immersed
in the solution; and slightly higher than the ceramic core of the calomel electrode.
A.2 Calomel electrode
When calomel electrode is in use, the rubber plug of the small hole at the top of the
electrode shall be pulled out to prevent diffusion potential from affecting the test results.
There shall be no bubbles in the potassium chloride solution in the electrode to prevent
disconnection. A small amount of potassium chloride crystals shall be kept in the
solution to ensure the saturation of the potassium chloride solution; but the potassium
chloride crystals shall not be too much to prevent blocking the electrode and the
passage of the measured solution.
When potassium chloride solution or crystals are attached to the surface of the
electrode, it shall be rinsed with water at any time.
A.3 Composite electrode
The protective cap on the lower end of the electrode shall be removed during use.
Avoid contact of the sensitive glass bulb of the electrode with hard objects to prevent
the electrode from failing. Put on the electrode protective cap after use; and put a small
amount of external reference replenishing solution (3mol/L potassium chloride solution)
in the cap to keep the electrode bulb moist.
If it is found that the replenisher in the protective cap is dry before use, it shall be
immersed in 3mol/L potassium chloride solution for several hours to ensure the
electrode performance.
When using, pull out the rubber plug or rubber sleeve of the small hole at the upper
end of the electrode to prevent the generation of diffusion potential and affect the
measurement result. When the electrode is not in use, the hole shall be blocked to