“I’d like a box of TLC plates, please.” Sounds innocent enough, right? But when you have more than 500 plate options, things get a whole lot trickier. How do you dig through the layers (pun intended) to get the plates you need?
TLC plates come in lots of fun forms and sizes—at least we think they’re fun! You can differentiate TLC plates by:
• Adsorbent material that makes up the layer itself
• Type of plate backing
• Layer thickness
• Plate size
• Fluorescent indicator – UV254 (yes or no)
• Format of scoring (or none)
• Preadsorbent zone (yes or no)
• Channeling (yes or no)
All clear now? Didn’t think so! In this first article of our two-part series, let’s look at the first four factors to help you make the right choice.
Most often, the actual layer is silica gel, but it can also be aluminum oxide, cellulose, microcrystalline cellulose, Florisil®, as well as various forms of modified silica gel such as reversed phase layers (C2, C8, C18), amino, cyano, and others. Which layer should you use? It depends on the compound you’re separating. Your best bet is to check what others have done first so you’re not reinventing the wheel. Historical data matters!
The layer’s backing is most often glass, because it can tolerate the most chromatography solvents. Using a flexible backing—namely polyethylene or aluminum—makes sense only when you must quickly and easily cut the plate (or sheet) into smaller sized pieces. Glass can also be cut or purchased pre-scored, so really it comes down to preference, availability, and price.
Thickness depends on the chromatographic separation you’re doing. For instance, the thickness for standard analytical TLC is 250um (1/4th of a millimeter). But for quantitative level analytical TLC, you’ll need a thinner plate—typically 200um, 150um, or even 100um. This category of TLC has a special name: high performance thin layer chromatography, or HPTLC. Meanwhile, thicker plates (500um, 1000um, 1500um, and 2000um) are best for preparative applications where you’re separating much larger samples. In this case, you’ll want to recover the separated sample components with a scraper or suction device.
This is a lot easier to figure out—whew! You just need to know about how many samples you want to run at the same time and what distance you need to chromatograph your samples for adequate separation. Standard sizes are 20×20, 10×20, 5×20, 10×10, 5×10, and 2.5×7.5 (microscope slide). Of course, all measurements are in centimeters. Additional specialty sizes are 2.5×10, 5×5, 2.5×5, and, our favorite, 20×40. Yes, you do need a very large custom developing tank for that one!
We hope this gets you on the right track when you need TLC plates. For more info, stay tuned for part II, where we explain fluorescent indicator, scored plates, preadsorbent zone, and channeling. We find this stuff so exciting and can’t wait to share it with you!
Have a great TLC day!