yes you can use c18 column, retention time of your analyte  will increase with compare to c8 column

A C8 and C18 column are almost the same (since they are both reverse phase columns) except that a C18 has a greater retention capacity and lower LOQ.  Thus, the switch may not affect your results as long as;

1.  The sample matrix does not interfere.

2.  You WILL have to adjust the mobile phase to obtain a similar chromatogram.

Not a big difference except it will affect the retention of your compounds, especially lipophilic compounds. You can have a look at the difference between C8 and C18 in the link attached.

Best of luck

http://www.sigmaaldrich.com/analytical-chromatography/hplc/columns/discovery-hplc/discovery-c18-c8-hplc-columns.html

 Thank you all. That was very helpful.

I think C8 column is advantage to separate the Divinyl Chl a from the pigment Chl a prominently than C18 column.