Spectrophotometric determination of nalidixic and pipemidic acids in a flow injection assembly with a solid-phase reactor as a highly stable reagent source

The flow-injection spectrophotometric determination of nalidixic (I) and pi pemidic (II) acids were can-led out by reaction with Fe(III) ions entrapped in a polymeric material and filling a packed-bed reactor; the released Fe( III) complexed with the quinolone is monitored at 426 nm. The method worked with a high reproducibility, even when using different reactors, days and solutions. Selectivity of the procedure was tested with different foreign c ompounds found in human urine as well as in pharmaceutical formulations con taining both quinolones; no relevant interferences were observed. The calib ration graph for (I) was linear over the range 1-250 mug ml(-1) with a rela tive standard deviation of 0.7% at 100 mug ml(-1) (n = 43). The calculated sample throughput was of 26 h(-1). The LOD was (s/n = 3) 0.1 mug ml(-1).The calibration graph for (II) was linear over the range 10-500 mug ml(-1) wit h a relative standard deviation of 1.1% at 150 mug ml(-1) (n = 40). The cal culated sample throughput was of 25 h(-1) and the LOD was (s/n = 3) 1 mug m l(-1). The method was applied to determine the (I) in pharmaceutical formul ations and of (II) in pharmaceutical formulations and human urine. (C) 2001 Elsevier Science B.V. All rights reserved.