Isopropyl alcohol

The nonwoven sample was used as a support layer to improve the mechanical strength, PVDF-PAA acted as a porous intermediate layer and GO acted a separation layer in the composite membrane, as shown in Figure 1. The vacuum filtration method was used to prepare the nonwoven/PVDF-PAA/GO composite [20 (link)]. In detail, the GO solution was prepared by dissolving dried GO in DI water via an ultra-sonication. Before the GO solution was deposited onto the surface of nonwoven/PVDF-PAA membrane, it was centrifuged (1000 rpm) at ambient temperature for 1 h to remove excessive large aggregates. Then, the GO suspension was filtrated through the two-component composite membrane using vacuum filtration by applying the suction force of a water aspirator with a wetting agent (2 mL isopropyl alcohol obtained from Mallinckrodt Baker Inc., Philipsburg, PA, USA). The GO deposition rate on the composite membrane was 0.097 ± 0.013 mg cm⁻² by filtering 10 mL of 200 ppm GO solution. The resulting membranes were dried in vacuum oven at 60 °C for overnight before filtration testing performance. The dried nonwoven/PVDF-PAA/GO sample was also denoted as three-component composite membrane.

The chemicals and solvents used for OTA extraction and for HPLC analysis were analytical grade or HPLC grade. The OTA standard used to prepare standard solutions for the validation of the applied methodology was obtained from Sigma-Aldrich Co. (St. Louis, MO, USA). Immunoaffinity columns used for samples purification (OchraTest™ WB) were purchased from Vicam® (Milford, MA, USA). PBS buffer pH 7.0 used during sample clean up procedure was prepared by dissolving sodium chloride (8.0 g), sodium phosphate dibasic (1.2 g), potassium phosphate monobasic (0.2 g), and potassium chloride (0.2 g) in purified water so as to obtain 1 litre of buffer. Water, acetonitrile, isopropyl alcohol, dichloromethane, and methanol were purchased from Mallinckrodt Baker B.V. (Deventer, The Netherlands); citric acid, phosphoric acid, sodium bicarbonate, sodium chloride, sodium phosphate dibasic, potassium phosphate monobasic, and potassium chloride were purchased from Carlo Erba Reagents (Cornaredo, MI, Italy); acetic acid and ethyl acetate were obtained from Sigma-Aldrich Co. (St Louis, MO, USA).