High purity acrylamide

High purity acrylamide, ¹³C₃-acrylamide and 5-hydroxymethylfurfural were purchased from Sigma-Aldrich (Diesenhofen, Germany). HPLC gradient grade acetonitrile and methanol were purchased from J.T. Baker (Deventer, Holland). All other chemicals used in this study were of analytical grade. Zorbax Extend-C18 column (250 × 4.6 mm, 5 μm) was purchased from Agilent Technologies (Santa Clara, CA, USA), and 0.45 μm PVDF (polyvinyl difluoride) filters Chromafil Xtra PVDF-45/25 from Macherey-Nagel (Düren, Germany). Ultra-pure water was used throughout the experiments (MilliQ system, Millipore, Bedford, MA, USA).
Stock solutions of acrylamide (1 mg/mL), ¹³C₃-acrylamide (1 mg/mL) and HMF (1 mg/mL) were prepared by dissolving in distilled water:acetonitrile (50:50 v/v). Working solutions were prepared by diluting the stock solution with water:acetonitrile (50:50 v/v) to concentrations of 0.75, 1, 2.5, 5, 10, and 25 ng/mL for acrylamide and ¹³C₃-acrylamide; 50, 100, 250, 500, 1000 and 2500 ng/mL for HMF. Stock solutions and working standards were kept at 4 °C. Carrez I solution was prepared by dissolving 15 g of potassium hexacyanoferrate in 100 mL of water, and Carrez II solution by dissolving 30 g of zinc sulfate in 100 mL of water.

Materials used in this study were corn grits, and hazelnut, camelina, pumpkin, and hemp seed press cakes. Press cakes were obtained by screw pressing in a screw expeller (Model SPU 20; Senta, Serbia) and were defatted via supercritical CO₂ extraction (custom-made extractor described by Jokić et al. [41 ]). These processes are described in detail in our previous article, with the same preparation for usage in the extrusion process, along with the approximate composition [18 (link)].
Gallic acid, Folin–Ciocalteu, DPPH, high-purity acrylamide, ¹³C₃-acrylamide, and 5-hydroxymethylfurfural were purchased from Sigma-Aldrich (Diesenhofen, Germany). HPLC gradient grade acetonitrile and methanol were purchased from J.T. Baker (Deventer, The Netherlands).