GB/T 9724-2007 English PDF (GBT9724-2007)

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GB/T 9724-2007: Chemical reagent -- General rule for the determination of pH
GB/T 9724-2007
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 71.040.30
G 60
Replacing GB/T 9724-1988
Chemical Reagent –
General Rule for the Determination of pH
(ISO 6353-1.1982, Reagents for chemical analysis -
Part 1. General test methods, NEQ)
ISSUED ON. SEPTEMBER 26, 2007
IMPLEMENTED ON. APRIL 1, 2008
Jointly issued by. General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of China.
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Normative References ... 4 
3 Method and Theory ... 4 
4 Reagent and material ... 5 
5 Instruments and equipment ... 6 
Annex A ... 8 
Foreword
This Standard is not equivalent to ISO 6353-1.1982 “Reagents for chemical analysis -
Part 1. General test methods".
This Standard replaces GB/T 9724-1988 "Chemical reagent - General rule for the
determination of pH". Compared with GB/T 9724-1988, the main changes are as
follows.
-- ADD the normative references (Chapter 2);
-- INCREASE the degree of accuracy of the acidometers (5.2);
-- ADD saturated calomel electrode with double salt bridge and composite
electrode (5.3 of this Standard);
-- DELETE antimony electrode (5.3.2 in 1988 edition);
-- ADD control of the operating conditions of the counter electrodes (Chapter 6 of
this Standard);
-- MODIFY contents in Annex A.
Annex A of this Standard is Informative.
This Standard was proposed by China Petroleum and Chemical Industry Association.
This Standard shall be under the jurisdiction of the National Technical Committee of
Standardization for Chemicals (SAC/TC63/SC3).
Drafting organization of this Standard. Shanghai No.4 Reagent and H.V. Chemical Co.,
Ltd.
Chief Drafting Staff. Jia Ling.
This Standard was first-time issued in 1988.
Chemical reagent -
General rule for determination of pH
1 Scope
This Standard specifies the general rules for measurement of pH of water solution in
electrometric method.
This Standard is applicable to the measurement of pH of chemical reagent and water
solution. The measurement range of pH is 1 ~ 12.
2 Normative References
The provisions in following documents, through reference in this text, constitute the
provisions of this Standard. For dated reference, all subsequent amendments
(excluding corrigendum) or revisions do not apply to this Standard, however, parties
who have reached an agreement on this Standard are encouraged to study whether
the latest revisions of these documents are applicable. For undated reference, the
latest revisions apply to this Standard.
GB/T 601 Chemical Reagent - Preparation of Standard Volumetric Solution
GB/T 603 Chemical reagent - Preparations of reagent solutions for use in test
methods (GB/T 603-2002, ISO 6353-1.1982, NEQ)
GB/T 6682 Water for laboratory use - Specifications (GB/T 6682-1992, neq ISO
3696.1987)
JJG 119- 2005 Verification Regulation of Laboratory pH Meters
3 Method and Theory
Soak the specified indicator electrode and reference electrode into the solution to be
measured to form a primary battery, whose electromotive force is related to the pH of
solution. The pH of the solution may be obtained through measurement of the
electromotive force of the primary battery.
(b) The reference electrodes shall use saturated calomel electrode, and Double
Salt Bridge saturated calomel electrode;
(c) The composite electrodes.
6 Measurements
Use non-carbon dioxide water to prepare the samples into 50 g/L solution (except
special case).
Prepare 2 kinds of standard buffer solutions - its pH values are respectively located at
both ends of pH values of the test solution, and near to the pH value of the test
solution. Calibrate the acidimeter with the above 2 kinds of standard buffer solutions;
turn the thermal compensation knob to the temperature of the standard buffer solution;
if the measured slope value is within the range of 90% ~ 100%, then the electrode is
in normal operating conditions. If the acidimeter does not have the function to adjust
the slope, it may use the 2 standard buffer solutions to calibrate each other; the pH
value error shall not be larger than 0.1 (if the slope value is less than 90% or the pH
value error is larger than 0.1, then the said electrodes shall be cleaned or replaced).
Use standard buffer solution whose pH is close to the test solution to conduct
positioning. Wash the electrode with water; scrub the electrode of the sample solution;
then adjust the temperature of the sample solution to 25±1°C; adjust the thermal
compensation knob of the acidimeter to 25°C; measure the pH of the sample solution.
In order to get precise results, the sample solutions shall be divided into 2 portions
and measured respectively; the measured pH values shall be stable for at least 1 min.
The permissible error of the measured pH value at the two times shall not be larger
than 0.02.
Annex A
(Informational Appendix)
Application and maintenance of the electrodes
A.1 Glass electrodes
Before use, new electrodes shall be soaked in the water for above 24 hours; after use,
it shall be rinsed immediately and be submerged in water for conservation.
A.2 Saturated calomel electrodes
During use, the rubber stopper on the small hole at the upper end of the electrode
must be pulled out to prevent diffusion potential that may impact the measurement
result. The potassium chloride solution inside electrodes must not have bubble to
prevent open circuit. There shall maintain some potassium chloride crystals in the
solution, so as to ensure that the potassium chloride is in saturation. The connecting
parts of the electrode shall not be stained or blocked, and to maintain appropriate
speed of effluent seepage.
A.3 Saturated calomel electrode with double salt bridge
The salt bridge sleeves shall be loaded with saturated ammonium nitrate or potassium
nitrate solution; other caution items are same as that of saturated calomel electrode.
A.4 Composite electrode
For the composite electrodes, the following matters shall be paid attention to.
(a) During use, the protective caps at the lower ends of the electrodes shall be
taken down to avoid connection of the sensitive glass bulbs with hard
substances, so as to avoid inactive electrode. After use, the protective caps shall
be put onto the electrodes, and reference feeding liquor of 3 mol/L potassium
chloride shall be filled inside the caps to maintain the moisture of the electrodes.
(b) Before use, if it is found that the feeding liquor inside the protective caps is dried,
they shall be soaked into 3 mol/L potassium chloride for several hours to
guarantee the service performance of the electrodes.
(c) During use, the rubber stopper on the small hole at the upper end of the
electrode must be pulled out to prevent diffusion potential that may impact the
measurement. It may fill 3 mol/L potassium chloride through the little hole. When