Diffusive Liquid Phase Microextraction (DLPME) as an efficient and rapid technique coupled with UV-Vis spectrophotometry – photo diode array detection was used in this research for extraction and measurement of methylphenidate (MPh) in water samples. This extraction method, is based on \"Homogeneous\" and \"Dispersive” liquid liquid extraction, and used of a ternary liquid system an organic solvent (lighter than water), as the extractor phase; diffuser solvent and aqueous sample solution [1]. After the extraction, the analyte carrier; an organic drop is introduced into the UV-Vis cell for determination of MPh. In the experimental section, main parameters which are affected on the extraction such as kind of organic solvent, diffuser solvent, phase volumes, extraction time, pH of sample solution, rate and time of centrifuge and effect of surfactant were optimized with “one variable-at-a-time” (univariate) process. But univariate is a strategy based on experience that does not guarantee the attainment of a true optimum of the extraction conditions [2]. Conversely, the chemometric approach relies on a rational experimental design, which allows the simultaneous variation of all experimental factors, saving time and materials [3]. Thus in the present study experimental design is applied to determine in an efficient way the set of conditions that are required to obtain a process with desirable, often optimal, characteristics [4]. For these reasons the microextraction procedure of methylphenidate (MPh) in water samples has been screened by a fractional factorial design with a twofold repetition of the center, in two levels. The optimization of seven operational parameters was carried out in a set of experiments developed by experimental design, which allow a rapid optimization with a minimal number of experiments. In this case, a surface response design with a two-fold repetition of the center and the multiple data analysis was employed. This comprises a total number of 40 experiments. Experimental design and statistical evaluation of the data obtained were made by means of the software package Statgraphics Centurion MINITAB14.

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