The determination of bifunctional compounds. IX. A selective reaction for the determination of guaifenesin in plasma by gas chromatography.

Guaifenesin after extraction from plasma with an organic solvent can be selectively derivatized with 2,4-dichlorobenzeneboronic acid and determined by gas chromatography with electron-capture detection. The detection limit for guaifenesin was 15 ng ml-1 for a 2.0-ml plasma sample. The mass spectra of the boronate derivatives of guaifenesin and mephenesin, used as internal standard, show good molecular ions with characteristic modes of fragmentation useful for their identification.