The RNA sample should be free of salts (e.g., Mg²+, or guanidinium salts), divalent cation chelating agents (e.g., EDTA, EGTA, citrate), or organics (e.g., phenol and ethanol). If an excess amount of genomic DNA is present in RNA samples, an optional DNase I treatment can be performed. DNase I should be inactivated/removed after treatment.