Yes, the Nucleoside Digestion Mix cannot digest an inverted 5´-ppp-5´ bridge (such as in m7G-G mRNA cap structures), thymine dimers or phosphothioesters. The Nucleoside Digestion Mix has reduced activity on oligonucleotides that have highly modified backbones with one or more substituents at the 2´, 4´ or 5´ ribose positions, such as antisense RNAs or other therapeutic oligonucleotides that have been engineered to resist nuclease cleavage. To ensure complete digestion, samples containing complex secondary structures and a large number of modifications (particularly modifications at the ribose 2´-position) may benefit from overnight incubation with the Nucleoside Digestion Mix in order to achieve complete digestion. Alternatively, the ratio of Nucleoside Digestion Mix:nucleic acid may be increased from 1 μl/μg substrate to 5-10 μl/μg substrate.