Talanta ELSEVIER Talanta 43 (1996) 1349-1356 Synchronous fluorimetric determination of salicylic acid and diflunisal in human serum using partial least-squares calibration A. Mufioz de la Peiia*, M.D. Moreno, I. Durhn-Me&, F. Salinas Departmmt of’ Analyrkal Chemisrry. L’nicrrsit~~ q/ E.~tremadura. 06071 Budajor. Spain Received 13 September 1995: revised 9 February 1996; accepted I9 February 1996 Abstract The simultaneous determination of salicylic acid and diflunisal in human serum has been accomplished by synchronous fluorimetry. in combination with partial least-squares multivariate calibration. The total luminescence information of the analytes has been used to optimize the spectral data set for the calibration, by analysis of the three-dimensional excitation-emission matrices. The synchronous spectrum, maintaining a constant difference of Ai. = 128 nm between the emission and excitation wavelengths, has been selected as optimum to perform the determination. The method is based on the fluorescence of these compounds in chloroform containing 1% (v/v) acetic acid. Serum samples are treated with trichloroacetic acid to remove the proteins, and both analytes are extracted into chloroform-l”/;) (v/v) acetic acid prior to the determination. For concentrations ranging from 60-240 pg ml-’ of each drug, analytical recoveries range from 96’1% to 103% for salicylic acid and from 97% to 105’X1 for diflunisal. &‘~‘ords: Diflunisal; Partial least-squares; Salicylic acid; Synchronous Fluorimetry 1. Introduction DiAunisal [2-hydroxy-5-(2,4-difluorophenyl) be- nzoic acid] is a ring-substituted salicylic acid derivative with analgesic and anti-inflammatory properties which make the drug useful for the treatment of osteoarthritis [l]. A comparison of the pharmacological profile of diflunisal with those of some well- known anti-inflammatory agents, such as aspirin, ibuprofen and in- domethacin, showed that diflunisal is more potent and less toxic than these drugs [2]. * Corresponding author. Two reports [3,4] have appeared demonstrating that diflunisal significantly interferes with salicy- late measurements in most methods used in the routine analysis of this drug: photometry, fluorimetry and fluorescence polarimetry. This in- terference is a problem if the salicylate concentra- tion determined by these methods is used for therapeutic monitoring, or in emergency toxicol- ogy screening of salicylate [3]. To analyze mixtures of salicylic acid and diflu- nisal in serum samples,gas chromatography [5] or high performance liquid chromatography [6] have been used. Recently, a non-chromatographic method has been proposed for the simultaneous determination 0039-9140/96/Sl5.00 C 1996 Elsevier Science B.V. All rights reserved PII SOO39-9140(96)01910-8