Spectrofluorimetric determination of anthranilic acid derivatives based onterbium sensitized fluorescence

Terbium sensitized fluorescence was used to develop a sensitive and simple spectrofluorimetric method for the determination of the anthranilic acid de rivatives furosemide and mefenamic and tolfenamic acids. The method makes u se of radiative energy transfer from anthranilates to terbium ions in alkal ine methanolic solutions. Optimum conditions for the formation of the anthr anilate-Tb3+ complexes were investigated. Under optimized conditions, the d etection limits are 6 x 10(-9), 1.4 x 10(-8) and 9.0 x 10-9 mol l(-1) for f urosemide, mefenamic acids and tolfenamic acid, respectively. The range of application is 2.5 x 10(-8)-5.0 x 10(-5) mol l(-1) for all three drugs. The method was successfully applied to the determination of furosemide and mef enamic and tolfenamic acids in serum after extraction of the samples with e thyl acetate, evaporation of the organic layer under a stream of nitrogen a t 40 degrees C and reconstitution of the residue with alkaline methanolic t erbium solution prior to instrumental measurement The mean recoveries from serum samples spiked with furosemide (5.0 x 10(-7), 2.0 x 10(-6) and 8.0 x 10(-6) mol l(-1)), mefenamic acid (3.0 x 10-6, 9.0 x 10-6 and 3.0 x 10(-5) mol l(-1)) and tolfenamic acid (3.1 x 10(-6), 12.5 x 10(-6) and 2.5 x 10(-5 ) mol l(-1)) were 96 +/- 8, 101 +/- 5 and 98 +/- 7%, respectively. The with in-run precision (RSD) for the method for two serum samples of each drug va ried from 2 to 8% and the day-to-day precision for two concentration levels varied from 2 to 13%.