Thin-layer chromatography (TLC) is a planar chromatography technique that in general separates a sample by normal-phase partitioning using a glass, plastic or metal surface commonly coated with silica particles as the stationary phase. Resolution can be adjusted through the thickness of layers and particle sizes, with finer particles providing an upgrade in resolution but a decrease in sample capacity.

Sample spotting is one of the most important steps in TLC. Manual application of samples near the edge of the plate is usually performed with a capillary tube, unless an automated sample applicator is used, in which case a precise volume is placed in a specific location on the plate. The plate is developed by exposing its edge to solvent. Samples are then carried via capillary action through the stationary phase by the solvent and eventually separated based on physical properties and absorption behavior between the mobile and stationary phases.

Analytes are visualized through a variety of means. For example, organic compounds are sprayed with iodine-based solutions to yield dark-colored spots. Other methods include incorporating fluorescent material into the stationary phase to be quenched by the analytes, producing locations which are read under UV light.

CAMAG’s ADC 2 Automatic Developing Chamber performs the film-development step of TLC without interference from potential environmental adulterants. Preset features include chamber saturation, developing distance, pre-layer conditioning, drying time, and humidity control and monitoring. Stand-alone operation is supplemented with remote control through the winCATS software.

The centrifugally accelerated CycloGraph by Analtech is for preparative TLC. Sample is introduced as a solution through a solvent pump or syringe into an absorbent ring in the rotor. Solvent mixture is then pumped at an adjustable speed through the absorbent ring until the sample components are separated by their affinity for the layer and solvent mixture. Individual rings are collected in a trough once on the outer edge of the rotor. The system is solvent compatible.

Merck Millipore’s (Merck KGaA) LiChrospher HPTLC plates use spherical silica particles 7 µm in diameter and a narrow particle-size distribution. The small particle size is intended for high-sensitivity TLC runs with low sample concentration and boasts low detection limits suitable for pharmaceutical compound assays and similar high-sensitivity applications. According to Millipore, the LiChrospher plates work faster than traditional HPTLC plates.

The TLC market is heavily driven by aftermarket sales. It has a value of approximately $60 million. End-market applications are concentrated in the pharmaceutical and agriculture industries, and general-testing labs. Methods-development labs are emerging as one of the primary bastions of TLC since the technology is employed for prescreening samples for HPLC and other, more expensive systems.

Thin-Layer Chromatography at a Glance:

Leading Suppliers

• CAMAG

• Thermo Fisher Scientific

• Merck KGaA

Largest Markets

• Pharmaceuticals

• Agriculture

• Independent Testing

Instrument Cost

• $100–$11,000