如何用薄层色谱区分苯胺、对溴苯胺或对氯苯胺

Fig. 6. Thin-layer chromatogram of some aromatic amines on silanized silica gel impregnated with 4% N- DPC solution. Migration distances, 12 cm; eluents, water-methanol-acetic acid (68.6:20: 11.4). (a) In-Bromoaniline; (b) o-bromoaniline; (c) p-bromoaniline; (d) p-chloroaniline; (m) mixture of chloro- and bromoanilines.
一篇文献有这样说，请高人们帮忙解释一下，是怎么操作的？！
先表示感谢！