Neutral Fraction
Definition
The organic phase recovered when the aqueous is buffered to pH 7 to 9 and extracted with a less polar solvent like methyl tert-butyl ether or ethyl acetate. Carries the weakly basic and neutral drugs: benzodiazepines, zolpidem, carbamazepine, phenytoin and legacy methadone and propoxyphene.
- Extraction pH
- 7 to 9
- Solvents
- Methyl tert-butyl ether, ethyl acetate
- Drug class
- Weakly basic and neutral drugs
- Examples
- Benzodiazepines, zolpidem, carbamazepine, phenytoin
Common questions
Why does the neutral fraction use a different pH than the acidic or basic fraction?+
Weakly basic and neutral compounds partition most efficiently into the organic solvent near physiological pH, unlike acidic drugs extracted at low pH or strong bases at high pH.
Why include a neutral fraction in systematic toxicological analysis?+
Benzodiazepines and related sedative-hypnotics, common in overdose and drug-facilitated crime casework, would be missed or poorly recovered by acidic or basic extraction alone.
Related terms
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- Alkaline Fraction
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- pKa
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- Post-Mortem Redistribution
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