GB/T 6283-2008 PDF English
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| GB/T 6283-2008 | English | 85 |
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Chemical products -- Determination of water Karl-Fischer method (general method)
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| GB/T 6283-1986 | English | 559 |
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Chemical products--Determination of water--Karl Fischer method (general method)
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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/GBT6283-2008
GB
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 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 & 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)
3 Principle
Any 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 Formula
5 Reagents and Materials
5.1 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 Apparatus
All 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 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
7.2.2 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 Method
8.1 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 Method
9.1 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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