Separation of nonsteroidal anti-inflammatory drugs by capillary electrophoresis using nonaqueous electrolytes

The aim of the present work was to investigate the separation of nonsteroidal anti-inflammatory drugs (NSAIDs: niflumic acid, flufenamic acid, piroxicam, alclofenac, tiaprofenic acid, flurbiprofen, suprofen, ketoprofen, naproxen, indomethacin, carprofen, indoprofen, sulindac) in capillary electrophoresis (CE) using completely nonaqueous systems. The influence of different parameters such as nature and proportion of organic solvent (methanol, acetonitrile, 2-propanol), apparent pH (ranging from 7 to 9) and temperature (ranging from 25 to 40 degrees C) on selectivity and migration times were studied systematically in an uncoated fused-silica capillary. A nonaqueous electrolyte made of 50 mM ammonium acetate - 13.75 mM ammonia in methanol proved to resolve 11 NSAIDs at 25 degrees C and 13 NSAIDs at 36 degrees C, both within 13 min and without a modifier besides the methanol itself. The same buffer containing 30% acetonitrile provides a satisfactory separation for 13 NSAIDs within 14 min at 25 degrees C.