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GB/T 6283-2008: Chemical products -- Determination of water Karl-Fischer method (general method) Delivery: 9 seconds. True-PDF full-copy in English & invoice will be downloaded + auto-delivered via email. See step-by-step procedure Status: Valid GB/T 6283: Historical versions
GB/T 6283-2008: Chemical products -- Determination of water Karl-Fischer method (general method)---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GBT6283-2008GB NATIONAL STANDARD OF THE PEOPLE’S 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 ContentsForeword... 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... 24ForewordThis 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 & 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 ScopeThis 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 ReferencesThe 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)3 PrincipleAny water (free or crystal water) present in the sample is quantitatively reacted with Karl • Fischer Reagent (a solution consists of iodine, sulfur dioxide, pyridine and methanol) of know titer.4 Reaction Formula5 Reagents and Materials5.1 Water Tested water shall meet the specification of Grade-III water stipulated in GB/T 6682. 5.2 Methanol Analytically pure. If the mass fraction of water in reagent is greater than 0.05%, add 50g of 5A molecular sieve into 500mL of methanol; plug the bottle stopper; place overnight; absorb the supernatant to use. 5.4 Iodine Analytically pure. 5.5 Pyridine Analytically pure. If the mass fraction of water in reagent is greater than 0.05%, add 50g of 5A molecular sieve into 500mL of pyridine; plug the bottle stopper; place overnight, absorb the supernatant to use. 5.6 Glacial acetic acid Analytical pure. 5.9 Anhydrous sodium sulfite Chemically pure. 5.10 Sulfur dioxide The sulfur dioxide both loaded with steel bottle and generated through sulfuric acid decomposing the sodium sulfite shall go through the dehydrating and drying treatment. The sulfur dioxide generation unit can refer to Appendix A. 5.11 Sample solvent The mixture containing 4 volumes of methanol and 1 volume of pyridine; or the mixture containing 4 volumes of ethylene glycol monomethylether and 1 volume of pyridine (especially applicable to the carbonyl-containing compound). In special cases, other solvent can also be used, such as glacial acetic acid, pyridine, or mixture containing 1 volume of methanol and 3 volumes of chloroform. 5.12 Desiccant 5.14 Sodium tartrate (Na2C4H4O6 • 2H2O) Analytically pure. 5.15 Water-methanol standard solution (10g water/L) Use micro burette or pipette to inject 1mL of pure water into fully dried 100mL volumetric flask containing about 50mL of methanol; 5.16 Water-methanol standard solution (2g water/L) Use micro burette or pipette to inject 1mL of pure water into fully dried 500mL volumetric flask containing about 100mL of methanol; 5.17 Silicone grease Used for lubricating frost glass joints.6 ApparatusAll used glassware shall be pre-dried at 130°C oven for 30min; then stored and cooled off in the desiccator containing the desiccant. 6.1 Direct titration (visual method or coulometric method) 6.1.1 The apparatus in this method can refer to Appendix C, the apparatus of this Standard consists of the following parts. 6.1.1.1 Automatic burette. 25mL, fine tip, scale division of 0.05mL, connect the protection tube filled with desiccant, and prevent the atmospheric moisture into the tube. 6.1.1.5 Reagent bottle with Karl • Fischer reagent, capacity 3L, brown bottle, filling tube inserting into automatic burette through the ground plug. 6.1.1.6 Bi-join rubber ball, connect with the drying bottle filled with desiccant; so that transfer the dry air to the reagent bottle, and fill the burette with the reagent. 6.1.1.7 End-point electricity measuring device, see Figure C.3 in Appendix C (visual method can be omitted). 6.1.2 Medical syringe, with appropriate volume, which has been corrected. 6.1.3 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. 6.2 Coulometric back-titration method 6.2.1 The apparatus in this method can refer to Appendix D; the apparatus of this Standard consists of the following parts. 6.2.1.5 Electromagnetic stirrer, fixed in the base with height adjustable; use outsourcing glass or Teflon soft steel rods to stir, the rotation speed is 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.7 Visual Method7.1 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 7.2.2 Determination Discharge the residual liquid in the titration vessel thoroughly through the discharge nozzle; use syringe, through the rubber plug, to inject 25mL (the stipulated volume of the to-be-tested specimen) of methanol or other solvent; 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. 7.3 Result expression 7.3.1 The titer of Karl • Fischer reagent T is expressed in mg/mL; and calculated by Formula (1) or (2). 7.3.2 Water content of specimen The water content of specimen X is expressed by mass fraction; and calculated by Formula (3) or (4).8 Direct Coulometric Titration Method8.1 End-point determination principle Ensure there is a potential difference between two platinum electrodes; when the solution contains water, the cathodic polarization reverses the current flow; then titrate the end-point through cathodic depolarization accompanied by abruptly increasing current (shown by suitable electrical device). 8.2 Operating procedures 8.2.1 Calibration of Karl • Fischer reagent the volume of consumed Karl • Fischer reagent (V3). 8.2.2 Determination Discharge the residual liquid in the titration vessel thoroughly through the discharge nozzle; use syringe, through the rubber plug, to inject 25mL (the stipulated volume of the to-be-tested specimen) of methanol or other solvent; start the electromagnetic stirrer; in order to react with slight amount of water in the methanol, add Karl • Fischer reagent stipulated in 8.2.1 till the ammeter pointer become skew abruptly, and maintain for at least 1min. 8.3.2 Water content of specimen The water content of specimen X is expressed by mass fraction; and calculated by Formula (7) or (8).9 Coulometric Back-Titration Method9.1 End-point determination principle Add excessive Karl • Fischer reagent, back-titrate with water-methanol standard solution. 9.2 Operating procedures 9.2.1 Calibration of Karl • Fischer reagent 9.2.1.1 Assemble the apparatus as per the Appendix D; lubricate the joint with silicone grease; use one automatic burette to add excessive Karl • Fischer reagent to the titration vessel; so that the electrodes are immersed; start the electromagnetic stirrer; connect with end-point electricity measuring device; then use the second automatic burette to titrate the standard water-methanol solution till the ammeter pointer suddenly is back to zero. 9.2.2 Corresponding values between Karl • Fischer reagent and standard water- methanol solution 9.2.3 Determination Discharge the residual liquid in the titration vessel thoroughly through the discharge nozzle; use syringe, through the rubber plug, to inject 25mL (the stipulated volume of the to-be-tested specimen) of methanol or other solvent; start the electromagnetic stirrer; in order to react with slight amount of water in the methanol, add excessive (about 2mL) Karl • Fischer reagent; then titrate water-methanol standard solution till the ammeter pointer is suddenly back to zero. 9.3 Result expression 9.3.1 The titer of Karl • Fischer reagent T is expressed in mg/mL; and calculated by Formula (9) or (10). ......Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al. 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