Methamphetamine (Meth), a psychotropic drug, raises serious social problems due to the increasing number of drug offenders and drug trafficking as it has become easier to buy Meth through the Internet. Therefore, rapid identification and semi-quantitative analysis of Meth are required for the narcotic investigators both in the field and laboratory. As a pre-liminary test for a fast and easy identification and economical analysis, three structurally similar amphetamine-like amine compounds (phenethylamines, PEs; phenethylamine (PE), N-methylphenethylamine (NM), DL-alpha-methylbenzylamine (DL)) were reacted with dabsyl chloride, a chromogenic derivatization reagent, on silica gel TLC plate, which can be identified with unaided naked eyes. Derivatives of PEs generated from direct reaction (in situ , co-spot) with derivatizing reagent were identified and used to determine the LOD. The TLC images were analyzed with densitometric image analysis programs to determine the repeatability and linearity of derivatization reaction for a potential method of semi-quantitative analysis.
PEs were reacted in situ (co-spot) to evaluate their derivatization reactivity in the pre-column mode on a silica gel TLC plate with Dabsyl-Cl as a derivatizing reagent. The derivatized products were identified under naked eyes without UV light at room temperature and the TLC image analysis of corresponding spots was performed using the densitometric image analysis for the semi-quantitative evaluation.
The derivatizing reagent (D), generated compounds containing strongly visible dabsyl- group on the TLC plate after reacting with PEs. However, a different reactivity of PEs with the D was observed. The LODs (imit of detection, 2 μL/spot, mg/mL) of PEs was in the low concentration range of 0.001 ~ 0.0025 mg/mL when the reaction spots were covered with cover-glass and heated at 70 oC for 10 min. which are similar to the LOD results using FMOC-Cl, but the higher LOD concentration range of 0.01 ~ 0.05 mg/mL was found at room temperature while exposed to air.
The RSD value (average, %) to test the repeatability of the derivatization reaction for PEs (0.5 mg/mL) was in the range of 0.5 ~ 3.3%. But a high RSD value range of 0.9 ~ 8.4% was shown at the low concentration (0.05 mg/mL) of PEs.
In the test of the linearity (R2) of the derivatization reaction at total concentration range (0.001 ~ 1.0 mg/mL) of PEs, the R2 values were in the range of 0.85 ~ 0.99 but a relatively good linear correlation was shown to be in the range of 0.98 ~ 0.99 between the areas of spots of generated derivatives and concentration of PEs (0.5 ~ 0.05 mg/mL).
To demonstrate the validity of the current method to be used for a semi-quantitative analysis of PEs by showing the high repeatability of a derivatization reaction at various concentration of PEs and corelationship, additional analytical test results are necessary such as the diverse changes of the concentration of derivatization reagents, the use of other reaction solvent, changes of reaction temperature, etc.