Adsorbents and Thin Layers

A variety of adsorbents such as silica gel, alumina, polyamide and cellulose are available commercially and are used to make thin layers for TLC. Alumina and silica gel are used with or without a suitable binder such as gypsum or starch. Mixtures of two adsorbents or adsorbents impregnated with certain reagents such as 8-hydroxyquinoline or different metal ions have also been used successfully to improve resolution.

Cellulose layers have several advantages: they are stable, they can be used with various specific reagents and they give reproducible data. They are particularly recommended for quantitative evaluation by den-sitometry. The drawbacks of cellulose layers are that corrosive reagents cannot be used and the sensitivities of detection reactions of certain amino acids are lower than on silica gel layers.

The best known and most widely used adsorbents for TLC purposes are from Merck, but other products can be used satisfactorily. Pre-coated plates are widely available and increasingly used for the investigation of amino acids and their derivatives. For example, ready-made cellulose layers from Macherey-Nagel (Germany) containing MN cellulose-300 in appropriately bound form are one of the best-known products. Chiralplate from the same firm and Chir from Merck, for the separation of enantiomers of amino acids and their various derivatives, contain a coating of reversed-phase silica gel impregnated with a chiral selector and copper ions. Using home-made thin-layer plates is possible and it is recommended that one should not change the brand of adsorbent during a particular set of experiments.

Application of mixed layers of cellulose and the ion exchanger Amberlite CG-120 and a double layer consisting of a 2 cm band of cellulose + cation exchanger (45 + 5 g) in aqueous CM-cellulose (0.05%), with the remaining portion of the layer prepared from cellulose SF suspension, have also been effectively used. A newly synthesized support named aminoplast comparable with that of starch and cellulose has been reported. Nevertheless, silica gel continues to be the most widely used and successful material.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook

Post a comment