Use of time-resolved lanthanide-sensitized luminescence for the kinetic determination of p-aminobenzoic acid

Lanthanide-sensitized luminescence was for the first time used to develop a simple kinetic method for the determination of p-aminobenzoic acid. The method is based on the formation of a complex with terbium(III) in the presence of trioctylphosphine oxide as synergistic agent and Triton X-100 as micellar medium. The high initial rate of the complex formation required the use of stopped-flow mixing technique in order to make kinetic measurements which, in addition, allows the method to be automated. Its analytical features compare very favourably with those described by using solid-surface room temperature phosphorescence in terms of rapidity, precision and selectivity. The initial rate is obtained within only 0.2 s after the reactants are mixed, which allows ready application of the proposed method to routine analyses. The calibration graph is linear over the range 0.08-4.0 mu g ml(-1) p-aminobenzoic acid and the detection limit is 0.02 mu g ml(-1). The relative standard deviation is close to 2%. The kinetic methodology avoids the effect of the sample matrix allowing the direct determination of this compound in pharmaceutical preparations. Analytical recoveries ranged between 98.6 and 113.0%. (C) 1998 Elsevier Science B.V.