A student was trying to run an agarose gel electrophoresis. She prepared a 2% gel in TBE buffer and loaded the gel with the sample and a DNA ladder. The gel was run in 1X TBE buffer at 100V for 45 minutes. The gel was then placed on a UV light box to visualize. To her surprise, she did not see any fluorescence in the RNA sample or the standard. What is the probable reason the gel could not be visualized?