Standard Test Method for Water Using Volumetric Karl Fischer Titration

Importancia y uso:

4.1 Titration techniques using KF reagent are one of the most widely used for the determination of water.

4.2 Although the volumetric KF titration can determine low levels of water, it is generally accepted that coulometric KF titrations (see Test Method E1064) 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.

4.3 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.

4.4 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 1: Some acids, such as formic, acetic, and adipic acid, are slowly esterified. 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).4

Note 2: 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 3: Weak amines are considered to be those with K_b value <2.4 × 10⁻⁵.

Note 4: Examples of stable ketones are diisopropyl ketone, camphor, benzophenone, benzil, dibenzolacetone, etc.

Note 5: Sulfuric acid up to a concentration of 92 % may be titrated directly; for higher concentrations see Note 13.

Note 6: Compounds subject to oxidation-reduction reactions in an iodine-iodide system interfere.

Subcomité:

D16.04

Referida por:

D0268-22, D1045-19, E1064-24, D8063-18, D1152-24, E1064-24, E0475-16, D1123-22A, D4815-22, D7862-21, D1152-24, D4274-23, D3218-07R18, E3050-24, D4928-12R18, D5983-21, D7785-21, D4171-22, D7618-13R21, D3401-97R22, D8375-23, D5008-22, D1992-17R22, D5798-21, D4806-21A, D8034_D8034M-24, C0465-23, C0465-23, D7058-19, D8235-21, E1417_E1417M-21E01, D5797-21, E0202-24, D4806-21A, E0222-23, D4815-22, D6160-21, D7995-19, D4672-24, E1064-24, D1631-24, D4252-89R17, D7923-19, D4017-22, D5372-20, D7544-23, D4806-21A, D6756-17, D6304-20, D4815-22, D5501-20, D6201-19A, D4928-12R18, D5501-20, D4928-12R18, D5501-20, E0200-23, D4252-89R17, D6304-20, D6304-20, D4928-12R18, D8375-23

Volúmen:

06.04

Número ICS:

71.040.40 (Chemical analysis)

Palabras clave:

free water; Karl Fischer reagent; pyridine-free; volumetric; water; water of hydration;