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GB/T 6283-2008 English PDF (GBT6283-2008)

GB/T 6283-2008 English PDF (GBT6283-2008)

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GB/T 6283-2008: Chemical products -- Determination of water Karl-Fischer method (general method)

This Standard specifies a general method for the determination of the free or crystal water content of a sample by the Karl Fischer visual method and the coulometric method.
GB/T 6283-2008
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 71.020; 71.040
G 04
Replacing GB/T 6283-1986
Chemical Products ?€? Determination of Water Karl ?€?
Fischer Method (General Method)
(ISO 760. 1978, Determination of Water Karl ?€? Fischer Method
(General Method), NEQ)
ISSUED ON. JUNE 18, 2008
IMPLEMENTED ON. FEBRUARY 1, 2009
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 ... 5
4 Reaction Formula ... 5
5 Reagents and Materials ... 5
6 Apparatus ... 8
7 Visual Method ... 10
8 Direct Coulometric Titration Method ... 12
9 Coulometric Back-Titration Method ... 14
Appendix A (Normative) Sulfur Dioxide Generating Equipment ... 18
Appendix B (Normative) Water-Methanol Standard Solution for Calibration of Karl ?€? Fischer Reagent ... 19
Appendix C (Normative) Visual 1) or Direct Coulometric Titrator ... 21
Appendix D (Normative) Coulometric Back-Titration Apparatus... 24
Foreword
This Standard is not equivalent for the degree of consistency with ISO 760.1978 Determination of Water Karl ?€? Fischer Method (General Method).
This Standard replaced GB/T 6283-1986 Chemical Products ?€? Determination of Water. Compared with GB/T 6283-1986, this Standard mainly has the following changes. --- Add the content of ?€?this Standard is not applicable to the sample that can react with the main components of Karl ?€? Fischer Reagent and produce water; neither applicable to the determination of water in sample that can reduce the iodine or oxidized iodide?€?;
--- Change the ?€?water equivalent?€? of Karl ?€? Fischer Reagent into ?€?titer?€?; --- Add the content of ?€?Select other formulation of Karl?€? Fischer Reagent on the market according to the nature of the sample?€?;
--- Rearrange the order of the standard appendixes.
This Standard?€?s Appendix A, B, C, D are the normative ones.
This Standard was proposed by China Petroleum and Chemical Industry Federation. This Standard shall be under the jurisdiction of National Technical Committee for Standardization of Chemical (SAC/TC 63).
Drafting organizations of this Standard. China Petroleum and Chemical Corporation Beijing Yanshan Branch, and Zhonghua Chemical Industry Institute of Standardization. Chief drafting staffs of this Standard. Cui Guanghong, Yang Jianhai, Weijing, Bi Xiaoxia, and Su Xiaoyan.
The historical edition replaced by this Standard is as follows.
--- GB/T 6283-1986.
Chemical Products ?€? Determination of Water Karl ?€?
Fischer Method (General Method)
1 Scope
This Standard specifies a general method for the determination of the free or crystal water content of a sample by the Karl ?€? Fischer visual method and the coulometric method.
This Standard is applicable to the determination of free or crystal water content in the most organic and o inorganic solid, liquid chemical products.
This Standard is not applicable to the sample that can react with the main components of Karl ?€? Fischer Reagent and produce water; neither applicable to the determination of water in sample that can reduce the iodine or oxidized iodide.
In some cases, the sample requires pretreatment measures, which shall be specified in the corresponding national standards.
When there is no instrument for the coulometric method, the visual method can be used; it is a direct titration, but only can used for the colorless solution. The coulometric method includes direct titration and back titration methods. No matter which titration is adopted, the result is more accurate; therefore, the coulometric method is recommended to be used.
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 Water for Analytical Laboratory Use - Specification and Test Methods (GB/T 6682-2008, ISO 3696.1987, MOD)
bottle with stopper; add about 85g of iodine, shake till the iodine is totally dissolved; then add 270mL of pyridine, tighten the stopper, shake till the fully mixing. Take the following methods to dissolve 65g of sulfur dioxide into the solution.
When injecting the sulfur dioxide, replace the stopper with a rubber plug where the thermometer, inlet glass tube (about 10mm from the bottle bottom, and tube diameter about 6mm), and air-ventilating capillary are equipped with.
Place the whole device and the ice bath on the balance, weight, accurate to 1g; use the hose to connect the sulfur dioxide steel bottle (or sulfur dioxide generator outlet) with drying tower filled with desiccant and air inlet glass tube; then slowly open the air inlet switch.
Adjust the flow rate of sulfur dioxide, so that it is completely absorbed; the liquid level in the inlet tube has no rising phenomenon.
As the mass slowly increases, keep balance through adjusting the balance weights, the solution temperature shall not exceed 20??C; when mass reaching 65g, immediately close the air inlet switch.
Quickly remove the connecting hose, then weigh the glass bottle and air inlet device; dissolve the mass of sulfur dioxide to be 60g~70g. Slightly excessive is not a problem. Tighten the stopper, mix the solution, leave it in the dark for at least 24h before use. The titer of such reagent is about 3.5mg/mL~4.5mg/mL. If it is prepared by methanol, it need day-to-day calibration; if it is prepared by ethylene glycol monomethylether, then it needn?€?t calibration.
Use sample solvent to dilute the prepared solution, then the Karl ?€? Fischer reagent with lower titer can be obtained.
The reagent shall be stored in the brown reagent bottle, placed in the dark, and prevent the influence from the atmospheric moisture.
NOTE. since the reaction is heat removing, from the beginning of the reaction, cool off the brown bottle, and maintain at about 0??C. E.g.. immerse into the ice batch or shredding solid carbon dioxide (dry ice).
In the newly prepared reagent, due to some unknown reactions, the titer of the reagent may decrease quickly at the beginning; after that it decreases very slowly. Other formulation of Karl ?€? Fischer reagent on the market can also be selected according to the sample nature. The determination result after such selection shall be consistent with that of preparing Karl ?€? Fischer reagent stipulated in this Standard. 5.14 Sodium tartrate (Na2C4H4O6 ?€? 2H2O)
150r/min~300r/min.
6.2.1.6 End-point electricity measuring device, see Figure D.3 in Appendix D. 6.2.2 Medical syringe, with appropriate volume, which has been corrected. 6.2.3 Small glass tube (called sample tube), one end closed, the other end sealed by rubber plug; used for weighing specimen and adding materials into the titration vessel; e.g.. weigh sodium tartrate (about 0.250g) for calibration of Karl ?€? Fischer reagent, or weigh solid specimen.
7 Visual Method
7.1 End-point determination principle
The color of iodine in the Karl ?€? Fischer reagent vanished as encountered water in the to-be-tested specimen; the first excessive drop of reagent shall show color. 7.2 Operating procedures
7.2.1 Calibration of Karl ?€? Fischer reagent
7.2.1.1 Assemble the apparatus as per the Appendix C. Lubricate the joints with silicone grease; use syringe, through rubber plug, to inject 25mL of methanol into the titration vessel; start the electromagnetic stirrer; in order to react with slight amount of water in the methanol, add Karl ?€? Fischer reagent with automatic burette, till the solution turns to brown.
7.2.1.2 In small glass tube, weigh 0.250g of sodium tartrate, accurate to 0.0001g; remove the rubber plug, add it swiftly into titration vessel within several seconds, then weigh the small tube, the mass of used sodium tartrate (m1) is determined through subtraction.
Also can use burette to add about 0.040g of water for calibration. Weigh the burette mass before and after the titration; the mass of used water (m2) is determined through subtraction.
Use water-methanol standard solution for calibration; refer to B.1 in Appendix B. Use Karl ?€? Fischer reagent for calibration to titrate the known amount of water till the solution turns to brown like the 7.2.1.1; then record the volume of consumed Karl ?€? Fischer reagent (V1).
7.2.2 Determination
Discharge the residual liquid in the titration vessel thoroughly through the discharge Where.
m0 ?€? specimen mass (solid specimen), in g;
V0 ?€?...

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