Separation of inorganic anions on hydrophobic stationary phases in ion chromatography

Inorganic anions were separated on hydrophobic stationary phases such as triacontyl-functionalized silica. Eluent conditions were examined in detail, and iodate, nitrate, iodide, and thiocyanate could be separated by using aqueous solutions. The effect of the eluent concentration on the retention of analyte anions was examined for a wide range of sodium sulfate concentrations of up to 1 M. The retention factor of hydrophobic anions decreased with increasing sodium sulfate concentration in the lower concentration region, while it increased with increasing sodium sulfate concentration in the higher concentration region. The addition of a small amount of an organic substance such as acetonitrile and tetraethylene glycol increased the retention of iodide and thiocyanate, while the addition of alcohols decreased their retention. Operating at lower temperature also increased the retention of analyte anions. It was expected that inorganic anions were retained on the stationary phase via hydrophobic interactions. The retention mechanism was discussed, considering the results obtained.