Capillary electrochromatographic separation of non-steroidal anti-inflammatory drugs with a histidine bonded phase

An open tubular wall-coated capillary column containing histidine functional groups was prepared and employed for the capillary electrochromatographic separation of non-steroidal anti-inflammatory drugs. The anion exchange along with the hydrogen bonding and hydrophobic properties of the surface coating allowed the separation of analytes with very similar ionic mobility. Selectivity and resolution were studied by changing the pH over the range from 3.5 to 5.0 and the concentration of the buffer from 10 to 25 mM, as well as variation of the organic modifier, such as methanol, ethanol and 1-propanol over the range 7.5 to 20%. The optimum experimental conditions for the separation of a drug mixture, which consisted of indoprofen, ketoprofen, suprofen, naproxen, flurbiprofen, fenoprofen and ibuprofen were using a mixture of acetate buffer (20 mM, pH 5.0)–ethanol (1:5, v/v) as background electrolyte and an applied voltage of −20 kV with UV detection at 220 nm. The separation of these drugs could be achieved with an average plate number of 1.0·105 m−1.