yes. it is, when the column adsorbs two components simultaneously, we have two breakthrough points. 

Dear Zainab, 

Usually breakthrough studies are performed on tracing the mobility of usually one (cation or anion) species at any given time. However, if the study is related to mixed contaminants, you can expect to have more than one breakthrough curve. However, you need to understand the fact that, both these curves may be totally dependent or totally independent.

Totally Dependent Case:

If the species (Cat-ionic or Anionic) exhibit co-precipitation behavior, the species with higher affinity exhibits the breakthrough first followed by lesser one's. I have not come across any study so far in my research life dealing with this. I believe this might be the case even with NAPL's. However, you need state-of-art equipment to tackle it.

Totally Independent Case:

If the species (Cat-ionic or Anionic) are relatively inert and exhibit different solubility product values, the one with higher solubility product will leach early followed by the one with least solubility product. This however has to do with the nature of hydro-metal-complexes (in case of metals) or hydro-complexes (organic or in-organic cases) that are being formed under given conditions. 

You need to be fundamentally pretty strong in interpreting the results. Remember, interpretation drawn can be justified from any angle and this gives rise to a lot of uncertainty. I suggest you to get good grip on basics before venturing into a problem of this complex nature. Should you need any help, do not hesitate to contact me. 

Best Wishes...

i agree with Arif

thank you all for your comments