Question

Please explain the scientific reasoning if the phenomenon below.

A nitration of phenol was carried out in orgo lab. the para and ortho isomers were then isolated by column chromatography. Before the process began, the vials collecting the fractions were weighed. After completing the chromatopgraphy, the vials containing the isolated profucts were left alone so the liquid could evaporate. Upon returning to the lab, the vials were weighed again. Although it appeared product was in the containers, the weight was exactly the same except for three vials. HOWEVER, when doing TLC from the products in the 10 vials... pure ortho isomers were formed even in each lane for the first 5 vials even though the weight suggested no gain in weight. How is it possible that there was no gain in weight of the vials but pure product was seen on the tlc? please expkain a scientific reasoning.