Thin layer chromatography (TLC) is an analytical separation technique where separation occurs on an open stationary phase layered on a support such as glass or plastic. High Performance TLC (HPTLC), a quantitative technique, is the semi- or fully automated sample application, plate development, and analysis. Absolute confirmation of contaminants separated by TLC is done using the ACQUITY QDa by directly interfacing the plate to the mass detector source inlet. A 200 mg capsule of Sheng Yuan Fang slimming product (herbal natural product) is weighed and dissolved in 10 mL methanol. Samples are homogenized for 30 seconds by vortex mixing and extracted in an ultrasonic bath for 10 minutes at room temperature. After centrifugation at 2750 RCF for 10 minutes at 25 °C, the supernatant is collected and used as test solution. Sibutramine reference material was purchased by Fluorochem (Derbyshire, UK) and prepared at a concentration of 0.785 mg/mL in methanol. 5 µL of sample, and 2 µL of standard were spotted onto an HPTLC Si 60 F254, 20 x 10 cm plate by the Automatic TLC Sampler 4 and developed in 9:1 toluene/methanol solution. The plate is derivatized then visualized under white light.
Target zones are directly eluted using the TLC-MS Interface 2 with oval elution head into the ACQUITY QDa at a flow rate of 0.5 mL/min with 0.1% formic acid in acetonitrile. The ACQUITY QDa is operated in positive electrospray ionization mode using the default settings: 0.8 kV capillary voltage, 15 V cone voltage, and 600 °C desolvation temperature. A full scan spectrum with the range of 50–650 m/z is acquired at a sampling rate of 10.0 points/sec (continuum). Data processing and evaluation of mass spectra are performed with Empower Chromatography Data Software. Figure 1 shows the QDa results from the TLC plate elution (Figure 2) of sibutramine standard (lane B) and slimming product (lane C).
