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 pipemidic (II) acids were carried 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 426nm. The method worked with a high reproducibility, even when using different reactors, days and solutions. Selectivity of the procedure was tested with different foreign compounds found in human urine as well as in pharmaceutical formulations containing both quinolones; no relevant interferences were observed. The calibration graph for (I) was linear over the range 1-250?gml-1 with a relative standard deviation of 0.7% at 100?gml-1 (n=43). The calculated sample throughput was of 26h-1. The LOD was (s/n=3) 0.1?gml-1. The calibration graph for (II) was linear over the range 10-500?gml-1 with a relative standard deviation of 1.1% at 150 ?gml-1 (n=40). The calculated sample throughput was of 25h-1 and the LOD was (s/n=3) 1 ?gml-1. The method was applied to determine the (I) in pharmaceutical formulations and of (II) in pharmaceutical formulations and human urine.