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This standard is drafted in accordance with the rules given in GB/T 1.1-2009.
This standard replaces QB/T 2724-2005 Leather - Chemical tests - Determination of pH
In addition to a number of editorial changes, the following technical changes have been made with respect to QB/T 2724-2005:
——— the requirement for determining the difference figure is added in Clause 4 "Principle";
——— the division value of pH meter is modified from 0.05 pH unit in the previous standard to 0.01 pH unit;
——— the accuracy of "6.3 Analytical balance" is modified from 0.05 g to 0.1 mg, which is consistent with the international standard;
——— in 6.4.1, the specification of wide-mouthed flasks is modified from 100 mL to 250 mL, which meets the test requirements and is consistent with the international standard;
—— in "7.1 Sampling", the requirement that "parallel sampling shall be conducted for determination" is clearly added;
——— In "8.1 Preparation of extraction solution", the oscillation time is modified to 6.0 h to 6.5 h, which is consistent with the international standard;
——— the "8.2 Determination of pH" in the previous standard is divided into "8.2.1 Calibration of pH meter" and "8.2.2 Determination of pH";
——— in "8.2.2 Determination of pH", the temperature for determination is modified from (20 ± 1) ℃ to (20 ± 2) ℃, which is consistent with the international standard.
This standard has been redrafted and modified in relation to ISO 4045: 2008 Leather - Chemical tests - Determination of pH. The method stated in ISO 4045: 2008 is based on the method standards listed in IUC 11 of International Union of Leather Technologists and Chemists Societies (IULTCS).
Many structural adjustments have been made with respect to ISO 4045: 2008, and a cross reference table for the clause number of this standard and those of ISO 4954:2008 is given in Annex A.
This standard includes technical changes with respect to ISO 4045: 2008.The clause and subclause concerned are identified by a vertical single line (|) located in the blank on its external margin of the page. These technical changes and reasons are listed in Annex B.
For the convenience of application, the following editorial changes have been made to ISO 4045: 2008:
——— foreword in ISO standard is deleted;
——— "this international standard" is modified to "this standard";
——— the comma used as decimal point "," is replaced by decimal point ".".
This standard was proposed by China National Light Industry Council.
This standard is under the jurisdiction of the National Technical Committee on Leather of Standardization Administration of China (SAC/TC 252).
This standard replaces the previous professional standard QB/T 2724-2005 Leather - Chemical tests - Determination of pH, which is abolished as of the implementation date of this standard.
The previous editions of this standard are as follows:
—— GB 4689.19-1984 (later modified into QB/T 3812.19-1984 with contents unchanged);
——— QB/T 3812.19-1999;
——— QB/T 2724-2005.
Leather - Chemical tests - Determination of pH
1 Scope
This standard specifies the methods for determining pH value and difference figure of aqueous extract of leather.
This standard is applicable to various types of leather.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 6682 Water for analytical laboratory use - Specification and test methods (GB/T 6682-2008, ISO 3696: 1987, MOD)
QB/T 2706 Leather - Chemical, physical and mechanical and fastness tests - Sampling location (QB/T 2706-2005, ISO 2418: 2002, MOD)
QB/T 2716 Leather - Preparation of chemical test samples (QB/T 2716-2018, ISO 4044: 2008, MOD)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
difference figure
It refers to the difference between solutions before and after the pH and the solution diluted 10 times
Note: difference figure is one way to measure the strength of acid and alkali, and its value will not exceed 1. If solution contains free strong acid (or free strong alkali), the value of difference figure is in the range of 0.7 to 1.0. The ionization of weak acid and alkali increases with the dilution of the solution, so the difference figure may only be used as a criterion for the presence of dissociated strong acids or alkali in the aqueous extract with a pH lower than 4.0 or higher than 10.0.
4 Principle
Aqueous extract is prepared from leather samples, and pH value of extract is determined with pH meter. If pH value is lower than 4.0 or higher than 10.0, difference figure shall be determined.
5 Reagents and materials
5.1 Distilled or deionized water, which meets the specification for Grade 3 water in GB/T 6682, with the pH value of 6 to 7 and the electrical conductivity not greater than 2×10-6s/cm in 20℃, shall be stored in boiled low-alkalic glass containers.
5.2 Buffer solution, used for the calibration of electrode system. Purchase and use the corresponding standard buffer solution according to the suggestions from pH meter manufacturers. The storage time of buffer solution depends on their composition and application method, so the accuracy of buffer solution shall be controlled. Buffer solution after use shall be discarded and shall not be reused.
6 Apparatus
6.1 Oscillator, the oscillation frequency shall set to (50 ± 10) r/min.
6.2 pH meter, with the measuring range of 0pH to 14pH unit and the division value of 0.01 pH unit, its electrode system shall be calibrated with standard buffer solution before measurement (5.2).
Note: Aqueous extract of leather with relatively grease sometimes may contaminate the electrode, in which case the film shall be gently wiped with absorbent cotton with acetone, or the electrode shall be immersed in a water-acetone mixture of 1:1 by volume. After cleaning the electrode, the film shall be completely immersed in water.
6.3 Analytical balance, with an accuracy of 0.1 mg.
6.4 Glass apparatus
6.4.1 Wide-mouthed bottle, 250 mL, with sealing plug.
6.4.2 Measuring cylinder, 100 mL, with the division value of 1 mL.
6.4.3 Volumetric flask, 100 mL.
6.4.4 Pipette, 10 mL.
Note: Glass apparatus shall be made of low-alkalic glass. Conduct blank test with distilled water before use. pH value and conductive property before and after the test shall be within the range specified in 5.1. Polyethylene and borosilicate glass should be used.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Reagents and materials
6 Apparatus
7 Sampling and preparation of samples
8 Procedure
9 Expression of results
10 Test report
Annex A (Informative) Cross reference for the clause and subclause numbers of this standard and those of ISO 4045:
Annex B (Informative) Technical differences between this standard and ISO 4045: 2008 and the relevant reasons
