Retention of arsenic species on zwitterionic stationary phase in hydrophilic interaction chromatography

Zwitterionic hydrophilic interaction chromatography (ZIC (R)-HILIC) was used to study the retention of selected organoarsenicals. The retention behavior of nine organic arsenic species on ZIC (R)-HILIC was investigated to elucidate which is the driving force for their separation, hydrophilic partitioning or adsorption driven by hydrogen bonds with surface H-donor/acceptor groups of the stationary phase. For this, the retention factor of the compounds k was correlated with log P-O/W and with the calculated strength of hydrogen bonding of the analytes. By examining aliphatic and phenylic compounds separately, improved correlation was received. This indicates that both phenomena contribute to the separation of these arsenic species on ZIR (R)-HILIC. The results obtained evidence that considerable electrostatic interactions also occur on ZIC (R)-HILIC. Retention behavior of arsenic species was investigated by varying the separation conditions, which shows that the composition of the eluent has a strong influence on the retention behavior. It is highly dependent on water/acetonitrile ratio, pH value and salt additives. Dissociation degree and polarity of arsenic species, which are varying with pH, regulate the distribution of arsenic species between stationary and mobile phases in HILIC. Increase in the ammonium acetate concentration leads to shortened or to prolonged retention depending on the structure of the arsenic species.