SPOTTING OF THE COMPONENTS
The following points may be strictly adhered to while spotting the component or mixture of components on a TLC plate, namely :
(i) The sample is normally applied as a solution in a ‘non-polar solvent’ as far as possible, since the use of a polar solvent may cause:
(a) spreading out of the starting spot, and
(b) affect directly the Rf value of components,
(ii) The solvent employed for dissolving the sample must be easily volatile-in-nature so that it should be removed from the TLC plate before development commences,
(iii) The ‘area of application’ should be smallest as far as possible so as to achieve a sharper resolution,
(iv) To maintain the size of the spot ‘small’ repeated applications is made by allowing the solvent to evaporate after each application. It can be easily achieved by :
(a) Pre-warming the TLC-plate, and
(b) Passing a stream of hot-air right below the sample spot (from a hair-drier).
(v) For exclusively ‘preparative work’ the sample is applied in a narrow-band the width of which must be kept as narrow as possible, and
(vi) Use of ‘spotting templates’, available commercially** may provide
(a) Device for making the ‘starting-line’
(b) Device for making the ‘finishing-line’, and
(c) Means for uniformly spacing the spots on the starting-line.