Flow injection spectrophotometric determination of the antibiotic fosfomycin in pharmaceutical products and urine samples after on-line thermal-induced digestion.

A new flow injection (FI) method for the precise and rapid spectrophotometric determination of the antibiotic fosfomycin (FMC) in urine and pharmaceutical samples is described. The method is based on the on-line quantitative thermal-induced digestion of the analyte prior to injection into the FI system. Ammonium persulfate was used as the oxidation reagent. The resulting orthophosphate ions were determined spectrophotometrically (lambda(max) = 690 nm) using the molybdenum blue approach. Chemical and FI variables that affected on-line oxidation were studied and optimized. The proposed method is very precise (s(r) = 1.2% at 1.0 x 10(-4) mol L(-1) FMC, n = 12), offers a high sampling rate of 60 h(-1), and allows for the determination of the analyte in the range 3.0 x 10(-6) to 3.0 x 10(-4) mol L(-1) with a satisfactory 3sigma detection limit of 1.0 x 10(-6) mol L(-1). Application of the proposed method to urine and pharmaceutical samples yielded accurate results with percentage recoveries in the range 96.4-102.5%. (c) 2002 Elsevier Science (USA)