In the analysis of ephedrine (EP) by gas chromatography/mass spectrometry (GC/MS), methcathinone (MC), a narcotic, has been detected as its artifact, and we investigated the formation mechanism of MC from EP. The effective analytical procedure which allows us to prevent its formation has been also examined. The injection temperature of the GC instrument was varied with different extraction solvents from aqueous EP solution, and the amount of MC as the artifact was measured.
As a result, the formation of MC from EP is attributed to 1) oxidation of EP by the oxidative impurities in the extracting solvent, and 2) oxidation of EP in the extremely high temperature of the GC injection appeared larger. Furthermore, as the procedure for preventing the formation of MC from EP, the injection method and derivatization of OH group of EP were also investigated.
In the extraction of EP, it was found that the use of high grade of extracting solvents such as ethyl acetate for synthesis grade, which contain the extremely low concentration of impurities that include dissolved oxygen and peroxide that cause oxidation of EP, is significantly effective for preventing the formation of MC from EP. Also, the use of split injection into GC in combination with protecting the OH group of EP by trifluoroacetyl derivatization allowed to prevent the formation of MC.
This study indicates that when a small amount of MC was detected in the GC/MS analysis of samples which contain high concentration of EP, careful examination will be needed in consideration of the possibility of the MC formation during the analysis. It will, also, be helpful for forensic analysis of other EP analogues including norephedrine and methylephedrine.
