Hello Ulfuara Shefa

The low 260/230 ratio is because of guanidine salts carry over to the sample. Increased absorbance at 230nm in RNA samples is due to contamination by guanidine thiocyanate, a salt which absorbs very strongly at 220–230nm at moderate or low salt concentrations, and can be present in the lysis buffer or extraction reagent (e.g., TRIzol) used in most RNA purification procedures.

The best approach would be to give more washes to the RNA sample. If you have used TRIzol, try washing with ethanol to desalt it. For silica preps, a few extra washes with 70-80% ethanol should clear the column of salts.

Also, I have listed two methods for desalting RNA.

1. You may use an ethanol precipitation with ammonium acetate, which is used in most cases. The purified RNA sample can undergo two precipitations. To form the pellet, one volume (V) of RNA to 3 V of chilled (–20°C) EtOH and 0.1 V of 4M ammonium acetate are mixed in a 1.7 mL microcentrifuge tube. The sample is placed on dry ice for 30–40 min, and then centrifuged for 30min at 13,000rpm. The supernatant is carefully removed from the RNA pellet, and the pellet is redissolved in RNase-free ddH2O (about 20μl), and the process is repeated. After the supernatant is removed the second time, 500μl of cold EtOH (–20°C) is used to wash the pellet, which is then dried in a speed vac and stored at –20°C until use.

OR

2. Desalting can also be accomplished by dialyzing the sample against RNase-free ddH2O. A 200μl RNA sample (with maximum 200μg) is dialyzed against 4 Litre of RNase-free ddH2O for 3 days with a complete change of ddH2O each day. The RNA is lyophilized to dryness, and then redissolved in nuclease-free water.

Best.