A new restricted access molecularly imprinted fiber for direct solid phase microextraction of benzodiazepines from plasma samples

Abstract

Restricted access molecularly imprinted polymers (RAMIPs) are hybrid materials that present selective binding sites for a template (or similar molecules), and an external hydrophilic layer that avoids the binding of proteins to the material, making them appropriate for the sample preparation of protein fluids. RAMIPs have been used successfully in online and offline solid phase extractions, but there is no application as a fiber in solid phase microextraction (SPME), to the best of our knowledge. In this paper, molecularly imprinted fibers were synthesized inside glass capillary tubes (0.53 mm i.d.), using diazepam and methacrylic acid as template and functional monomer, respectively. The MIP fibers were coated with a cross-linked bovine serum albumin (BSA) layer, resulting in RAMIP fibers that were used in the SPME of benzodiazepines directly from biological fluids. The BSA layer acts as a protective barrier that avoids the binding of proteins from the sample by an electrostatic repulsion mechanism. The protein exclusion capacity of the RAMIP fiber was about 98%, which is selective to benzodiazepines in comparison with other drugs (citalopram and fluoxetine). The SPME was optimized and the extraction conditions were set as follows: 1000 μL of the sample diluted with water (1 : 0.5, v : v), no pH adjustment, an extraction time of 20 min at 500 rpm, and elution with 200 μL of acetonitrile for 5 min at 500 rpm. The fibers were used in the SPME of benzodiazepines directly from plasma samples, followed by HPLC-DAD analyses. The method was linear for bromazepam (50–750 μg L⁻¹), clonazepam (15–250 μg L⁻¹), alprazolam (15–350 μg L⁻¹), nordiazepam (100–2100 μg L⁻¹) and diazepam (100–2600 μg L⁻¹), with correlation coefficients higher than 0.97. Relative standard deviations (precision) and relative errors (accuracy) ranged from 0.5 to 20.0%, and −15.6 to 21.6%, respectively.