AQUAMICRON™ Scope of Applications for Karl Fischer Method
The Karl Fischer method can be used with a wide range of substances. However, the method depends on a kind of iodometry based on the reaction between the Karl Fischer reagent and water. The results will therefore show a positive error if the sample includes substances that react with iodine, and a negative error if the sample includes substances that produce iodine by oxidizing iodide compounds. The following tables list substances that can be titrated directly with Karl Fischer reagents, substances that cannot be titrated directly but can be titrated by means of adjustments based on appropriate chemical reactions or processes, and substances that react with Karl Fischer reagents and are therefore unsuitable for direct titration. Even if a substance cannot be titrated directly, its moisture content can be measured by indirect means, such as the water vaporization method.
Compounds that can be titrated directly
| Organic compounds |
| Hydrocarbons(saturated, unsaturated compounds) Alcohols, Polyhydric alcohols, Phenols, Ethers Inert ketones(diisopropyl ketone, et al) Inert aldehydes(formaldehyde, chloral, et al) Organic acids, Hydroxylic acids, amino acids Acid anhydrides Esters, Lactones, Inorganic acid esters Amines( Nitriles, Cyanhydrins, Cyanic acid derivatives Nitro compounds, Oximes, Hydroxamic acids Thiocyanate, Thioethers, Thioesters Halogenated hydrocarbons, Halogenated acyls Sugars, Organic salts and their hydrates |
| Inorganic compounds |
| Inorganic salts and their hydrates Inorganic acids Chelate compounds Fertilizers Calcium carbonate Polytungsten salts |
Compounds that react with Karl Fischer reagents and cannot be titrated directly
| Organic compounds |
| Ascorbic acid, Diacyl peroxides Peracids, Quinone |
| Inorganic compounds |
| Sodium sulfide, Sodium peroxide Chromates, Dichromates Ferric oxide, Nickel oxide, Arsenic trioxide Arsenates, Arsenites, Borates, Boron oxide Hydrogencarbonates, Carbonates Metal hydroxides, Metal oxides Sulfites, Pyrosulfites Sodium nitrite, Thiosulfates Cupric salts, Stannous salts |
Compounds that can be titrated directly after special processing or under certain conditions
The examination will be necessary for the following compounds though it was said that these could be titrated directly by the following treatments in former references.
| Compound | Treatment |
| Ammonia | Add acetic acid. |
| Ferric salts | Add 8-hydroxyquinoline. |
| Hydrazine derivatives | Add acetic acid. |
| Hydroxylamine salts | Add sulfur dioxide: pyridine solution (1:1). |
| Thiol(mercaptan) | Prevent interference by adding olefins(octene, etc.). |
| Sulfuric acid | If the sulfuric acid is 92%pure or higher, add a large surplus of pyridine and titrate it as a salt. |
| Thioacid | Prevent interference by adding olefins(octene, etc.). |
| Thiourea | Prevent interference by adding olefins(octene, etc.). |
Examples of how AQUAMICRON™ can be used with compounds that cause interference
| Compound | Interference reaction | Treatment | |
|---|---|---|---|
| Volumetric titration | Coulometric titration | ||
| Ketones | React with methanol to produce ketal and water | Titrant SS-Z + Solvent KTX | AKX ＋ CXU |
| Titrant SS + Solvent CP | |||
| Aldehydes | React with methanol to produce acetal and water React with sulfur dioxide and water | Titrant SS-Z + Solvent KTX | AKX ＋ CXU (suitable only for a certain aromatic aldehydes) |
| Titrant SS + Solvent CP | |||
| Lower carboxylic acids | React with methanol to produce ester and water | Titrant SS-Z + Solvent KTX | AKX ＋ CXU |
| Titrant SS + Solvent CP | |||
| Amines above pKa 9 （above pKa 9） |
Consume iodine gradually and the end-point becomes unstable | Titrant SS-Z ＋ Solvent GEX salicylic acid 10g |
AXI or AX + CXU / salicylic acid 10g |
| Titrant SS ＋ Solvent MS salicylic acid 10g |
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