ASTM E203-2008
用卡尔费休试剂检验水的标准试验方法
Standard Test Method for Water Using Volumetric Karl Fischer Titration
ASTM E203-2008 中，可能用到以下耗材
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- 适用范围
Titration techniques using KF reagent are one of the most widely used for the determination of water.
Although the volumetric KF titration can determine low levels of water, it is generally accepted that coulometric KF titrations (see Test Method E 1064
) are more accurate for routine determination of very low levels of water. As a general rule, if samples routinely contain water concentrations of 500 mg/kg or less, the coulometric technique should be considered. Applications can be subdivided into two sections: (1) organic and inorganic compounds, in which water may be determined directly, and (2) compounds, in which water cannot be determined directly, but in which interferences may be eliminated by suitable chemical reactions or modifications of the procedure. Further discussion of interferences is included in Section 5 and Appendix X2.
Water can be determined directly in the presence of the following types of compounds:
Organic Compounds Acetals Ethers Acids (Note 1) Halides Acyl halides Hydrocarbons (saturated and unsaturated) Alcohols Ketones, stable (Note 4) Aldehydes, stable (Note 2) Nitriles Amides Orthoesters Amines, weak (Note 3) Peroxides (hydro, dialkyl) Anhydrides Sulfides Disulfides Thiocyanates Esters Thioesters Inorganic Compounds Acids (Note 5) Cupric oxide Acid oxides (Note 6) Desiccants Aluminum oxides Hydrazine sulfate Anhydrides Salts of organic and inorganic acids (Note 6) Barium dioxide Calcium carbonate Note 18212;Some acids, such as formic, acetic, and adipic acid, are slowly esterified. For high accuracy with pyridine-based reagents, use 30 to 50 % pyridine in methanol as the solvent. When using pyridine-free reagents, commercially available buffer solutions can be added to the sample prior to titration. With formic acid, it may be necessary to use methanol-free solvents and titrants (1).
Note 28212;Examples of stable aldehydes are formaldehyde, sugars, chloral, etc. Formaldehyde polymers contain water as methylol groups. This combined water is not titrated. Addition of an excess of NaOCH3 in methanol permits release and titration of this combined water, after approximate neutralization of excess base with acetic acid (see Note 9).
Note 38212;Weak amines are consid.........