Surface Imprinting of Silica Gel by Methyldopa and Its Application in the Solid Phase Extraction Procedure

An imprinted amino-functionalized silica gel material was prepared by surface molecular imprinting technique combined with a sol-gel process on the supporter of activated silica gel and used as a solid-phase extraction for the extraction and determination of methyldopa (MTD). Non-imprinted silica adsorbent was synthesized without the addition of MTD using the same process. MTD-imprinted and non-imprinted silica adsorbents were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and the static adsorption experiments. The prepared MTD-imprinted silica sorbent demonstrated high adsorption capacity and significant selectivity for MTD in the presence of competitive substances. The maximum adsorption capacity of surface imprinted and non-imprinted silica adsorbent for MTD were 14565.81 and 2990.56 µg g -1, respectively. The imprinted 3-aminopropyl triethoxysilane (APS) modified silica gel adsorbent provided fast kinetics for the adsorption of MTD. In the operational mode of solid phase extraction (SPE), calibration curve of MTD solution was linear in the range of about 15 to 100 µg mL -1. The limit of detection (LOD) and precision (RSD) during five replicates were 2.31 µg mL -1 and 5.69%, respectively. At last, the MTD-imprinted material was used as SPE adsorbent to determine the MTD in non-spiked and spiked pharmaceutical samples with satisfactory recovery higher than 94%.