Dansyl chloride derivatization of methamphetamine: a method with advantages for screening and analysis of methamphetamine in urine

The screening and quantitation of methamphetamine (MP) in urine using dansyl chloride (DNC) as the derivatization reagent were studied. Urinary MP derivatized with DNC could be detected by visual observation of the fluorescence in a solid-phase extraction column such as a Sep-Pak C18 cartridge to which the whole reaction solution was applied. The DNC-derivatized MP was eluted from the cartridge and then identified and quantitated by gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC). In the GC-MS analysis with the MS detector in the electron-impact mode, DNC-derivatized MP and amphetamine (AP), exhibited diagnostic molecular ion peaks. The intensities of the molecular ions were 15% (DNC-MP) and 35% (DNC-AP) of the base peak (a fragment ion because of the loss of dimethylnaphthalene from M+), demonstrating that this method of derivatization has a major advantage for confirming APs by GC-MS. MP derivatized with DNC could be determined by HPLC with ultraviolet detection. Because a good correlation (r = 0.95) between the GC-MS and HPLC method for urinary MP was confirmed, both HPLC and GC-MS appear to be useful tools for determining urinary MP. The intensity of the cartridge fluorescence due to DNC-derivatized MP was approximately related to the urinary content of MP determined by HPLC or GC-MS, although a false positive in the visual fluorescence was observed in some urinary specimens from healthy volunteers. From these results, screening and confirmation/determination following DNC derivatization is proposed as a suitable method for the analysis of MP.