Horizontal and radial development

In this method, a square or rectangle of paper is laid horizontally on glass rods in a shallow, covered tray-type tank ( Speedi-Cell , Schaar and Co., Chicago), and the end of the paper nearest the origins is dipped into a solvent trough [40]. The compact size of the apparatus allows development in an oven or refrigerator at various temperatures. 

Development can also be between glass or aluminum plates. This method is especially advantageous for volatile compounds, and generally increased reproducibility oi Rp values has been claimed [37]. A small chamber for fast, horizontal PC has been described [41]. 

If multiple samples are applied in a circle (ca. 1-2 inch diameter) about the center of the paper where the wick joins and solvents flow in, the individual samples form segments instead of concentric circles. This allows comparison of standards and unknowns on the same sheet [44,45]. 

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