I need to some serial dilutions of RNA targets for RT-PCR following in vitro transcription. At the moment the RNA is about 2 ug/ul, or 10^12 copies /ul, and I need to get down to <50 copies/ul. I have tried ultra pure water, but the RNA appears to be sticking together, as the dilutions cease being linear after the 1/100 dilution (I am doing a 10-fold dilution series). I have also tried 1 mM citrate, which seems better, but still isn't great.
Does anyone know a good diluent that will reduce/remove intermolecular interactions, so I can get an accurate dilution series? Or are there any good tips out there for diluting RNA quantitatively?