| Fraction | Compound classes |
| Hydrophobic | |
| Acids | Strong acids Humic and fulvic acids, high molecular weight alkyl monocarboxylic and dicarboxylic acids, aromatic acids |
| Weak acids Phenols (e.g., lignin), tannins, medium molecular weight alkyl monocarboxylic and dicarboxylic acids | |
| Bases | Proteins, aromatic amines, high molecular weight alkyl amines |
| Neutrals | Hydrocarbons (e.g., terpenoids), aldehydes, high molecular weight methyl ketones and alkyl alcohols, ethers, furans, pyrrols |
| Hydrophilic | |
| Acidsa | Hydroxyl acids, sugars, sulphonics, low molecular weight alkyl monocarboxylic and dicarboxylic acids |
| Bases | Amino acids, purines, pyrimidines, low molecular weight alkyl amines |
| Neutrals | Proteins, carbohydrates (e.g., polysaccharides, low molecular weight alkyl alcohols, aldehydes and ketones), cellulose and cellulose derivatives |