Manual sample application methods using hand-held devicesare a poor choice if scanning densitometry is used for detec-tion. Lane scanning of samples applied as spots requires that thestarting position of each spot is accurately known. This is easilyachieved with mechanical applicators that utilize a grid mecha-nism for sample application. Also, the sample must be applied tothe layer without damaging the surface, which is nearly impossibleto achieve using manual sample applicators. When fixed-volumedosimeters are used for sample application, it is important thatsamples and standards are applied in the same solvent and of iden-tical volumes. This ensures that starting zones of the same size andshape are formed. Spray-on sample applicators are a better choicewhenever samples or standard solutions of different volumes areused in quantitative thin-layer chromatography.