Development of a membrane solid-phase extraction method based on polyethyleneimine modified MWNTs for on-line extraction and preconcentration of acidic proteins in serum samples

Abstract

A membrane solid-phase extraction method based on polyethyleneimine modified multi-walled carbon nanotubes (MWNTs) for the on-line separation and concentration of acidic proteins in serum sample, followed by UV-Vis spectrophotometric determination, is developed. In this study, the polyethyleneimine was noncovalently adsorbed on the outer surface of the MWNTs and then the polyethyleneimine modified MWNTs (PEI–MWNTs) were filtered through a membrane to form an adsorbent layer. The alkalescent PEI coating provided high-density homogeneous functional groups on MWNTs' sidewall and led to homogeneous dispersion of MWNTs in aqueous solutions. The PEI–MWNTs membrane was applied to on-line separation of proteins in serum and exhibited excellent extraction and concentration ability for acidic proteins. Factors, which affected the efficiency of proteins extraction and their subsequent spectrophotometric determination, were studied and optimized. Under optimized conditions, the retention and recovery efficiencies of 100% and 92% for 25 μg mL⁻¹ of BSA solution were achieved, along with a RSD value of 1.9% at a flow rate of 30 μL s⁻¹. The limit of method detection was 1.0 μg mL⁻¹ with an enrichment factor of 12. The maximum adsorption capacity for BSA was 112 mg g⁻¹ MWNTs. The method was applied to isolating acidic proteins from bovine serum sample and obtained satisfactory results.