TLC-analysis in forensic sciences using a diode-array detector

HPTLC (High Performance Thin Layer Chromatography) is a well known and versatile separation method which shows many advantages when compared to other separation techniques. The method is fast and inexpensive and does not need time-consuming pretreatments. For visualisation of the sample distribution on a HPTLC-plate we developed a new and sturdy HPTLC-scanner. The scanner allows simultaneous registrations of spectra in a range from 198 nm to 612 nm with a spectral resolution of better than 0.8 nm. The on-plate spatial resolution is better than 160 mum. The measurement of 450 spectra in one separation track does not need more than two minutes. The new diode-array scanner offers a fast survey over a TLC-separation and makes various chemometric applications possible. For compound identification a crosscorrelation function is described to compare UV sample spectra with appropriate library data. The cross-correlation function herein described can also be used for purity testing. Unresolved peaks can be virtually separated by use of a least squares fit algorithm. In summary, the diode arry system delivers much more information than the commonly used TLC-scanner.