ORIGINAL The Effects of Stationary Phases on Retention and Selectivity of Oligonucleotides in IP‑RP‑HPLC

nucleotide mers that are composed of a purine or pyrimi-dine base, pentose sugar and phosphate residues [1]. Natu-ral oligonucleotides exist in the form of small RNA mole-cules or intermediates derived from the breakdown of large nucleic acids [2]. Oligonucleotides may be also chemically synthesized and used in various fields of science, including as primers for DNA amplification in the polymerase chain reaction (PCR) or as therapeutics against cancer and viral infection [3–6]. The critical requirement for these com-pounds is their high purity. Quality control of synthetic oligonucleotides, determination of shorter ones and related compounds is usually accomplished by chromatographic techniques, especially ion-pair high-performance liquid chromatography (IP-RP-HPLC) [7–15]. The separation of oligonucleotide depends on two mechanisms: hydropho