This standard specifies the principle, instruments and utensils, reagents and solutions, determination steps and result calculation method for the determination of water-soluble ash alkalinity in tea. This standard is applicable to the determination of water-soluble ash alkalinity in tea. GB/T 8309-2002 Determination of water-soluble ash alkalinity in tea GB/T8309-2002 Standard download decompression password: www.bzxz.net

GB/T8309—2002
This standard is a revision of GB/T8309--1987 "Determination of Alkalinity of Water-soluble Ash in Tea". This standard is equivalent to ISO1578:1975 "Tea--Determination of Alkalinity of Water-soluble Ash". The main difference between this standard and ISO1578:1975 is that 2g of sample is used to prepare 150mL of water-soluble ash solution, and the alkalinity of the sample is calculated after neutralization with a certain concentration of acid. ISO1578:1975 uses 5g of ash to prepare 60ml of water-soluble ash solution, and the alkalinity of the sample is calculated after neutralization with acid.
This standard is revised mainly in accordance with the requirements of GB/T1.1-1993 "Guidelines for Standardization Work Unit 1: Rules for Drafting and Presentation of Standards Part
1: Basic Regulations for Standard Writing", and some modifications are made to GB/T8309-1987 in terms of format and text. The specific technical content has not changed, and only the content of "8.2 Repeatability" has been added. This standard will replace GB/T8309-1987 from the date of implementation. This standard is proposed by the All-China Federation of Supply and Marketing Cooperatives. This standard is under the jurisdiction of the Hangzhou Tea Research Institute of the All-China Federation of Supply and Marketing Cooperatives. The drafting unit of this standard: Hangzhou Tea Research Institute of the All-China Federation of Supply and Marketing Cooperatives. The main drafters of this standard: Guan Huixian and Sha Haitao. This standard is interpreted by the Hangzhou Tea Research Institute of the All-China Federation of Supply and Marketing Cooperatives. 1.33
GB/T8309—-2002
ISO Foreword
The International Organization for Standardization (ISO) is a world federation of international standardization bodies (ISO member bodies). The work of developing international standards is usually done by ISO technical committees. Member bodies interested in the work of a technical committee have the right to participate in the technical committee. Other international organizations, whether official or unofficial, also participate in its work through liaison with ISO. After the international standard is approved by the ISO committee meeting, the draft international standard is formally adopted by the technical committee and submitted to the member bodies for voting. ISO procedures require at least 75% of the member bodies participating in the voting to formally adopt it. Prior to 1972, the results of the work of technical committees were published in ISO recommendations, which are now being forwarded as international standards. As part of this process, Technical Committee ISO/TC34 has summarized ISO Recommendation R1578 and found it technically suitable for forwarding. Therefore, International Standard ISO1578 replaces ISO Recommendation R1578:1970, which is technically identical. The ISO recommended standard was approved by the following countries: 23 countries including Australia, Brazil and the United States approved it, and no member opposed the recommendation. No member opposed the forwarding of ISO/R1578 as an international standard. 34
1 Scope
National Standard of the People's Republic of China
Determination of alkalinity of water-soluble ash content in tea
Tea---Determination of alkalinity of water-soluble ash contentGB/T 8309--2002
eqv ISO 1578:1975
Replaces GB/T8309---1987
This standard specifies the principle, instruments and utensils, reagents and solutions, determination steps and result calculation methods for the determination of alkalinity of water-soluble ash content in tea.
This standard applies to the determination of alkalinity of water-soluble ash content in tea. 2 Cited standards
The clauses contained in the following standards constitute the clauses of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T602—1988 Preparation of standard solutions for determination of impurities in chemical reagents GB/T8302—2002 Tea Sampling
GB/T 8303—2002
Preparation of ground samples and determination of their dry matter content Tea
GB/T8306-2002 Tea
Determination of total ash
GB/T 8307--2002
3 Definitions
Determination of water-soluble ash and water-insoluble ash Tea
The following definitions are adopted in this standard.
Alkalinity of water-soluble ash The amount of acid required to neutralize the water-soluble ash leachate, or the amount of alkali equivalent to the amount of acid. 4 Principle
Use methyl orange as an indicator and titrate the solution from the water-soluble ash with a standard hydrochloric acid solution. 5 Instruments and appliances
Conventional laboratory instruments and the following items:
5.1 Burette: 50ml.
5.2 Erlenmeyer flask: 250mL.
6 Reagents and solutions
6.1 Hydrochloric acid: 0.1mol/L standard solution, prepared and calibrated according to GB/T602. 6.2 Methyl orange indicator: 0.5g of methyl orange, dissolved in hot distilled water and diluted to 1L. Approved by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China on June 17, 2002 and implemented on December 1, 2002
7 Determination procedures
7.1 Sampling
According to GB/T8302.
7.2 Sample preparation
According to GB/T8303.
7.3 Preparation of water-soluble ash solution
According to GB/T8307.
7.4 Determination
GB/T 8309—2002wwW.bzxz.Net
After cooling the water-soluble ash solution, add 2 drops of methyl orange indicator (6.2). Titrate with 0.1 mol/L hydrochloric acid solution (6.1). 8 Calculation of results
8.1 Calculation method
Expression of alkalinity: the number of moles of hydrochloric acid of a certain concentration required to neutralize 100g of dry ground sample, or converted to the mass fraction of potassium hydroxide contained in the dry ground sample. 8.1.1 Alkalinity is expressed in moles (100g of dry ground sample) and calculated according to formula (1): V
10 X M. X m
Where: V——volume of 0.1mol/L hydrochloric acid standard solution consumed during titration, mL; M. —mass of sample, g;
substance content (dry state) of sample, %.
(titration concentration]
Note: If the concentration of the hydrochloric acid standard solution used is not accurate to the concentration required by 6.1, a correction factor of 0.1 is used in the calculation!
8.1.2 Alkalinity is expressed as the mass fraction of potassium hydroxide and calculated according to formula (2): Water-soluble ash alkalinity (%) = 10×1 000×M.×m56V
Where: V, M, m are the same as in 8.1.1, and "56" is the molar amount of potassium hydroxide. If the requirements of repeatability (8.2) are met, the arithmetic mean of the two measurements is taken as the result (keep one decimal place). 8.2 Repeatability
The difference between the two measured values ​​of the same sample shall not exceed 0.2g per 100g of sample. 136
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