I have MASSES of experience with Agilent arrays. I find that the easiest way to concentrate RNA is to vauum-dry it (SpeedVac) at ~45oC! It also eliminates the worry about differential precipitation of small and large RNA. In fact, I haven't bothered bringing the RNA to the recommended concentration for years. Instead, I aliquot the right amount of RNA into the wells/tubes, dry to completion, and resuspend in the mastermix with water added to the right final volume.

The reason I started doing it is that at least the miRNA arrays are sensitive to salt, so I was trying to avoid another ethanol precipitation with potential salt carryover.

I have not tried Glycogen, but linear acrylamide does not inhibit anything.

Hello Anna Git,  thank you! SpeedVac sounds good option, How long do you put the RNA samples in SpeedVac? please! Regards! :)

The time depends on the parameters of your equipment (strength of vacuum, ventilation, temperature), the initial volume and the shape of the tube: round bottom dries faster than conical, but the pellet is broader so be careful when resuspending.

Anna Git, thank you so much! i did it, the results were very well!