Ultrathin-Layer Chromatography Plates

A miniaturized planar chromatography system assembled from an ordinary consumer ink-jet printer for application of low-nanoliter volumes and a flat bed scanner for documentation and quantification was proposed for determinations on monolithic and nanostructured ultrathin-layer chromatography (UTLC) phases (29). The system was shown, using dye mixture test solutions, to outperform existing TLC instruments for analysis on miniaturized plates with analyses performed in minutes, numerous samples run in parallel at reduced cost, and very low sample and reagent volumes, by using a familiar computer interface with common office peripherals. Commercial glass plates (6 × 3.6 cm) coated with a 10 µm thick monolithic silica gel layer (EMD/Millipore) and glass backed plates (5 or 10 × 2 cm) coated by depositing SiO₂ hexagonal spiral nanostructures at a deposition angle of 84° in a 10-µm layer were developed in a small TTC chamber (29). The goal is to eventually develop a fully online, automated system for rapid, routine analysis.

Miscellaneous Layers

Polygram Ionex-25 (Macherey-Nagel) are polyester sheets coated with a 0.2-mm mixed layer of silica, a polystyrene-based strong acid cation or strong base anion exchange resin, and a binder. They are suited for separation of organic compounds with ionic groups, such as amino acids and inorganic ions.

Impregnated layers

Layers have been impregnated with various buffers, chelating agents, metal ions, or other compounds to aid resolution or detection of certain mixtures (impregnation reagents are tabulated in reference 12).

Analtech precoated silica gel plates are available already impregnated with potassium oxalate to facilitate resolution of polyphosphoinositides, magnesium acetate for phospholipids, 0.1 M sodium hydroxide for organometallics and acidic compounds, and silver nitrate for argentation TLC. Analtech manufactures plates containing ammonium sulfate for detection of compounds as fluorescent or charred zones after heating (vapor-phase fluorescence or self-charring detection).

Macherey-Nagel sells silica gel G plates with ammonium sulfate for separation of surfactants and caffeine-impregnated plates for charge-transfer TLC, used in the separation of polycyclic aromatic hydrocarbons (PAHs).

The most common impregnation reagent is silver, which allows separation of organic compounds with unsaturated groups such as fatty acids and sterols through p-complexation.

Mixed-Phase Layers

Mixed-phase layers have been homemade with a particular ratio of sorbents for specific applications. In addition, Macherey-Nagel offers the following 0.25-mm precoated mixed layers: aluminum oxide G/acetylated cellulose for separation of PAHs; cellulose/silica for separation of preservatives; and kieselguhr/silica for carbohydrate, antioxidant, and steroid separations. Analtech sells Avicel cellulose-DEAE cellulose (9 + 1) layers that have a lower ion-exchange capacity and higher mobility for negatively charged molecules than DEAE alone.