Digitally Enhanced Thin-Layer Chromatography: An Inexpensive, New Technique for Qualitative and Quantitative Analysis

842 Journal of Chemical Education • Vol. 84 No. 5 May 2007 • www.JCE.DivCHED.org Thin-layer chromatography (TLC) is often used as a qualitative method. It can determine the number of components in a mixture, verify the identity of substances, monitor the progress of a reaction, or ascertain the effectiveness of a purification. Since TLC is so easy and practical, many chemists frequently use TLC methods in their labs. Quantitative TLC analysis is typically the province of HPTLC (high-performance TLC). HPTLC plates have finer particles than regular TLC plates, and consequently they are better suited for quantitative analysis, although they are more costly. HPTLC samples are applied by mechanical applicators (dosimeters) and analyzed with automated equipment, such as a TLC scanner. Unfortunately, the equipment for quantitative TLC analysis is expensive—CAMAG’s TLC Scanner 3 costs about $30,000 with the software needed for analytical work. The documentation system, DigiStore 2, from CAMAG costs $17,500 but needs Videoscan software ($6,300) to do analysis (1). This equipment fills a specific niche in the market for production-oriented systems (mainly large companies that need automated equipment for processes such as food analysis); however, it is not practical for small companies and labs that also do analysis. High schools and colleges that cannot afford such equipment are limited to regular TLC, thus their students do not acquire experience with quantitative methods. This study shows that if digital photography is combined with regular TLC (“digitally enhanced” or DE-TLC), it can perform highly improved qualitative analysis as well as make accurate quantitative analysis possible for a much lower cost than commercial equipment (a quality digital camera costs about $500, and the software is free). Researchers have used a CCD camera to do quantitative TLC analysis (2–4), while another researcher used a scanner with visible light to do TLC analysis (5). All of the research projects used HPTLC plates except Johnson (5). Four of the research projects used fluorescent HPTLC plates (2, 3, 6, 7). In general, the use of expensive equipment, such as TLC scanners and costly video cameras, has been the norm for quantitative analysis. DE-TLC is the first technique to use a digital camera and software analysis to separate red, green, and blue brightness values in an image of a TLC plate to create multispectral scans. It is like a “poor man’s” spectrophotometer, and it is easy to utilize. DE-TLC uses commonly available fluorescent TLC plates (not HPTLC plates), a digital camera with manual exposure control, and conventional TLC equipment. DE-TLC can be used at any institution, but it is especially appropriate for high schools and colleges that do not have the budget to pay for more expensive equipment for TLC analysis.