A method for nalidixic acid (NA) determination by transmitted room-temperature phosphorescence is proposed. The antibacterial agent NA in acidic solution shows native fluorescence; when NA is spotted on
a filter paper precoated with beta -cyclodextrin and lead (II) acetate and dried for 5 min, phosphorescence results. The transmitted phosphorescence was measured directly with the use of a homemade sample
holder. The excitation and emission wavelengths were 330 and 417 nm, respectively. The applicable concentration range was between 0.06 and 4.50 mu g/mL with a relative standard deviation of 2.8% and a detection
limit of 0.02 mu g/mL. The method was applied to the determination of NA in human urine and pharmaceuticals, with recoveries from 97.5 to 105.5%.
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