Study of the Performances of Thin Layer Chromatography. IV--Optimization of Experimental Conditions

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Abstract
The experimental conditions which permit the achievement of a given separation by TLC are discussed from a theoretical standpoint. The minimum analysis time increases as the third power of the necessary plate number, hence, it is practically impossible to separate substances with a relative retention smaller than 1.2 or a ΔRf smaller than 0.05. Minimum analysis time is achieved for an Rf value close to 0.50. These facts are in excellent agreement with observations by practitioners. There is an optimum particle diameter which increases with increasing necessary number of theoretical plates. Contrary to what happens in column chromatography, because the law which controls flow rate is different, the finer particles must be used to achieve the easier separations. This explains why analysis time increases so fast with plate number. The optimum particle diameter is not very critical, but analysis time increases rapidly if particles smaller than ⅔ or larger than twice the optimum diameter are used. Consequently, the analyst needs three particle sizes for each stationary phase grade, for example 5, 10, and 20 μm. The temperature has little effect in the general case, except through the change of Rf and relative retention.

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