Chemometric assisted solid-phase microextraction for the determination of anti-inflammatory and antiepileptic drugs in river water by liquid chromatography diode array detection

M. MARTÍNEZ GALERA; L. VERA-CANDIOTI; M.D. GIL GARCÍA; H.C. GOICOECHEA

San Sebastián, España

Congreso; XV Reunión Nacional de la Sociedad Española de Química Analítica; 2009

Environmental sample matrices such as ground superficial and waste-waters are complex samples, often containing compounds which can interfere with the compounds of interest, so that direct analysis may not be possible and, moreover, pharmaceuticals are generally found in these matrices at trace concentration levels. Therefore, it is necessary to perform an initial sample preparation step, including purification and concentration of the analytes. Sample preparation may be achieved by a wide range of techniques but all of them shows the two above mentioned goals, in addition to provide a robust and reproducible method which is independent of variations in the sample matrix [1]. Even though traditional sample-preparation methods are still in use (e.g. solid phase extraction, SPE), trends in recent years are focused towards smaller initial simple sizes, small volumes or no organic solvents, greater specificity or greater selectivity in extraction and increased potential for automation. Solid phase microextraction (SPME) is a modern sampling preparation technique for isolating and preconcentrating organic compounds, which is in compliance with all these requisites and, additionally, is highly sensitive and can be used for polar and no polar analytes.   In the present work, an analytical method for the simultaneous determination of seven non steroidal anti-inflammatory drugs (naproxen, ketoprofen, diclofenac, piroxicam, indomethacin, sulindac and diflunisal) and the anticonvulsant carbamazepine is reported. The method involves preconcentration and clean-up by SPME using polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibers, followed by liquid chromatography with diode array detection analysis (LC-DAD). Parameters that affect the efficiency of SPME step such a soaking solvent, soaking period, desorption period, stirring rate, extraction time, sample pH, ionic strength, organic solvent and temperature were investigated using a Plackett-Burman screening design. Then, the factors presenting significant positive effects on the analytical response (soaking period, stirring rate, stirring time) were considered in a further central composite design (CCD) to optimize the operational conditions for the SPME procedure. Additionally, multiple response simultaneous (MRS) optimization function was used to find the optimum experimental conditions for the on-line SPME procedure. The best results were obtained using a soaking period of 5 min, stirring rate of 1400 rpm and stirring time of 44 min. The use of SPME avoided matrix effect and allowed to quantify the analytes in river water samples by using Milli-Q based calibration graphs. Recoveries ranging from 71.6 to 122.8 % for all pharmaceuticals proved the accuracy of the proposed method in river water samples. Method detection limits were in the range of 0.5 to 3.0 mg L-1 and limits of quantitation were between 1.0 and 4.0 mg L-1 for pharmaceutical compounds in river water samples. The expanded uncertainty associated to the measurement of the concentration ranged between 8.5% and 29.0% for 20 mg L-1 of each analyte and between 9.0% and 29.5% for the average of different concentration levels.