In this thesis a fast, sensitive, and simple method based on magnetic nanoparticles (M) modified -3-(trimethoxysilyl)-1-propanthiol as an adsorbent has been developed for extraction, preconcentration, and determination of trace amounts of Cd (II) in environmental samples. These magnetic nanoparticles can be easily dispersed in aqueous samples and retrieved by the application of external magnetic field via a piece of permanent magnet. The main factors affecting the extraction efficiency such as pH value, sample volume, eluent concentration, stirring time, and interferences ions have been investigated and established. Under the optimal conditions, high preconcentration factor (333) were achieved. The limits of detection was as low as 0.07 µg L ? 1 . The prepared sorbent was applied for preconcentration of trace amounts of Cd (II) in the various water samples with satisfactory results. In the second work the applicability of microporous membrane based liquid–liquid–liquid microextraction was evaluated for the extraction and preconcentration of chloropromazine prior to their determination by differential pulse voltammetry. The target drug was extracted from 5 mL of aqueous solution (donor phase, 0.08 M NaOH) into an organic extracting solvent (n-dodecane) impregnated in the porous of a polymeric microporou membranec and finally back extracted into 200 µL of aqueous acidic solution located inside the extraction cell. In order to obtain high extraction efficiency, the parameters affecting the extraction including pH of the source and receiving phases, the type of receiving and organic phases, ionic strength, stirring rate and extraction time were studied and optimized. Under the optimized conditions, enrichment factors up to 18.5 were achieved .The calibration curve were obtained in the range of 0.005–75 µM with reasonable linearity ( R 2 0.99 ) and a limit of detection of 0.0025 µM (based on S/N = 3). The results indicated that Microporous membrane based liquid–liquid–liquid microextraction method has excellent clean-up and high preconcentration factor and can be served as a efective and sensitive method for monitoring of the drug in biological samples.