Analysis of street Ecstasy tablets by thin layer chromatography coupled to easy ambient sonic-spray ionization mass spectrometry
reported were obtained after background subtraction and by averaging ca five scans. Samples (caffeine standard solution and tablets) were diluted in HPLC grade methanol to give a final concentration of 1 mg mL-1, and 1 μL was introduced via manual injection. The GC temperature program used consisted of an initial temperature of 130 °C for 1 min then increased to 280 °C at 17 °C min-1 and held for 11 min. Results and Discussion TLC separation of the seven common ecstasy tablet components was evaluated using four different solvent systems as eluents (Table I). CHCl3/CH3OH (50/50 v/v) was inefficient since it caused spot tailing for most standards and ecstasy samples tested. CHCl3/CH3OH/CH3COOH (20/75/5 v/v) provided well defined spots for both the samples and standards, but MDMA, metamphetamine, amphetamine, and ketamine presented too close Rf values (0.62-0.71). The best results were obtained for CH3CH(CH3)OH/CH3OH (95/5 v/v) and, most particularly, for CH3OH/NH4OH (98/2 v/v) (Figure 3). Although close Rf values for MDMA (main drug expected in ecstasy tablets) and metamphetamine were observed, good separation and resolution was observed for MDA, MDEA, amphetamine, ketamine, and caffeine (Figure 3 and Table I).
TLC/EASI-MS For TLC, we selected therefore CH3OH/NH4OH (98:2) v/v as the best eluent and the components of each spot (Figure 3) were then subjected to desorption, ionization, and m/z measurements by EASI-MS in the positive ion mode using acidified methanol as the spray solvent. Table I. Rf values for the seven drug standards as a function of different TLC eluents
Compound
CHCl3: CH3OH (50:50) v/v
CHCl3: CH3OH: CH3COOH (75:20:5) v/v
CH3OH: NH4OH (98:2) v/v
CH3CH(CH3) OH:NH4OH (95:5) v/v
MDEA
0.62
0.74
0.71
0.87
MDA
0.48
0.60
0.67
0.81
MDMA
0.37
0.64
0.56
0.62
Metamphetamine
0.35
0.62
0.57
0.62
Amphetamine
0.71
0.66
0.66
0.70
Ketamine
0.86
0.71
0.84
0.80
Caffeine
0.84
0.94
0.77
0.70
Figure 4 shows the “on-spot” EASI-MS acquired directly from the surface of the TLC spots of each of the seven standards used. Note the unambiguous characterization of each drug, mostly as a single ion (which facilitates spectra interpretation and analyte characterization) corresponding to their protonated molecules, that is, [M + H]+. MDEA was the only drug that was also detected as [MDEA + H20 + H]+ and [MDEA + Na]+. Signal-to-noise ratio was quite high for all standards except caffeine (Figure 4). LOD was evaluated for TLC of MDMA and found to be of 3 ± 0.3 μg. For the caffeine spot, the low sensitivity of EASI-MS seems to result from its polarity and high affinity to silica that hampered desorption from the TLC plate by the EASI droplets containing acidified methanol. We are currently searching for an EASI-spray solvent or mixture of solvents that could provide proper desorption and ionization of caffeine from the silica in TLC spots.
Figure 3. TLC data for the seven common ecstasy components tested as well as for the 25 samples of apprehended street ecstasy tablets using CH3OH:NH4OH (98:2) v/v as the eluent. Spots developed by UV are represented by dark black or gray (less intense) ovals.
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Br J Anal Chem