Dispersive solid phase extraction using magnetic nanoparticles performed in a narrow-bore tube for extraction of atorvastatin, losartan, and valsartan in plasma

Sample preparation is an essential step in most analytical procedures. Solid phase extraction (SPE) as a powerful clean–up method has drawbacks such as: clogging of cartridges, being time–consuming, necessity of pump usage, low extraction efficiency resulted in particles aggregation, and impossibility of treatment of large sample volumes [1]. New SPE methods have attracted special attention in recent years and proposed for resolving the SPE problems. Magnetic solid phase extraction (MSPE) is one of the new SPE procedures which uses magnetic sorbents to adsorb analytes. These sorbents can be separated easily using an exterior magnetic force from the aqueous solution. Then, a suitable solvent is used for desorption of the analytes for further determination [2, 3]. Magnetic nanoparticles (MNPs) are a kind of nanoparticles which are presenting super-paramagnetism and also possess unique reactivity and large specific surface area due to its nano nature. Bare MNPs are seldom used in extraction methods because of lack of functional groups to interact with the analytes, aggregation tendency resulting in loss of their magnetism, quick biodegradation, and easily oxidation in air. Thus, MNPs are coated by silane groups for preventing aggregation and oxidation by air and to functionalize of them with different groups which make the sorbents suitable to interact with the interested analytes [4]. In this study, a new version of MSPE performed in a narrow–bore tube has been proposed. For this purpose, hydrophobic octyl (C8) functionalized Fe3O4 MNPs stabilized by SiOH groups (Fe3O4@SiO2@C8) are used as the magnetic sorbents for the extraction of atorvastatin, losartan, and valsartan from human plasma prior to their determination by HPLC–PAD. After precipitation of the plasma proteins, the supernatant is diluted with deionized water and filled into the narrow–bore tube. Then mg–level of the sorbent is added into the tube. The sorbent is dispersed and moved down through the solution instead of passing the solution from the cartridge used in the conventional SPE. Using an external magnet, the collected sorbents at the bottom of the tube are transferred to top of the solution and released to move down through the solution for three times to increase the extraction efficiency. Finally the adsorbed analytes are desorbed by µL–level of methanol and injected into the separation system. Under the optimum extraction conditions LODs and LOQs were in the range of 0.05–0.07 and 0.16–0.24 mg L-1, respectively. The method was used for the determination of the selected pharmaceuticals in human plasma samples.