Fraction B
Definition
The alkaline chloroform extract obtained after basifying the residual aqueous to pH 9 to 10 with ammonium hydroxide and partitioning with chloroform. Contains the basic alkaloids: morphine, codeine, strychnine, atropine, nicotine, quinine and cocaine.
- Extraction pH
- 9 to 10
- Basifying agent
- Ammonium hydroxide
- Solvent
- Chloroform
- Compound class
- Basic alkaloids
- Examples
- Morphine, strychnine, cocaine, nicotine
Common questions
Why is chloroform used for Fraction B while ether is used for Fraction A?+
The choice reflects the classical Stas-Otto scheme's solvent optimisation for each compound class; chloroform's polarity and partitioning behaviour favours the alkaloid bases being extracted at high pH, while ether was found more effective for the acidic and neutral compounds pulled at low pH.
Why does the residual aqueous need to be basified before extracting Fraction B?+
Basic alkaloids like morphine and strychnine only become un-ionised and lipid-soluble enough to partition into an organic solvent when the surrounding solution is alkaline, so raising the pH to 9-10 is what allows them to move out of the water layer.
Is the Stas-Otto Fraction A/B scheme still used in modern forensic toxicology labs?+
It is largely historical; most modern labs use solid-phase extraction or liquid-liquid extraction protocols tailored to specific drug panels paired with LC-MS/MS, though the acidic/basic fractionation logic behind Stas-Otto still underlies how extraction pH is chosen today.
Related terms
- Ammonium Sulphate Modification
- The Otto variant in which saturated (NH4)2SO4 is added to a protein-rich homogenate (liver, kidney, blood) to salt out proteins before partitioning....
- Colour Spot Test
- A presumptive identification reaction in which a small amount of concentrated fraction is treated with a chromogenic reagent (Marquis, Mecke, Mandelin, Mayer,...
- Defatting
- A clean-up step before partitioning in which the acidified aqueous is washed with petroleum ether or n-hexane to remove fats, waxes and...
- Fraction a
- The acidic ether extract obtained by partitioning the acidified aqueous tissue digest with diethyl ether at pH 2 to 3. Contains barbiturates,...
- Stas-Otto Method
- Sequential acid-alkaline solvent partitioning that isolates organic poisons from biological matrix in two fractions: acidic ether (Fraction A) for acidic and neutral...