K2s2o8

6-Hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox, 97%) and n-alkane standard solution C₇-C₃₀ (1000 μg/mL each component in hexane) were purchased from Sigma-Aldrich Chemie (Taufkirchen, Germany); 2-(3-hydroxy-6-oxo-xanthen-9-yl)benzoic acid, fluorescein (FL) and 2,2′-azobis-2-methyl-propanimidamide dihydrochloride (AAPH) were from Fluka Analytical (Bornem, Belgium); NaCl, KCl, KH₂PO₄ and K₂S₂O₈ were from Lach-Ner (Brno, Czech Republic); Na₂HPO₄ was from Merck KGaA (Darmstadt, Germany); carbon dioxide and nitrogen gases (99.9%) were from Gaschema (Jonava, Lithuania). International Calibration Extract 4 (ICE-4), containing α- and β-acids (10.98% of cohumulone; 31.60% of humulone+adhumulone; 13.02% colupulone; 13.52% lupulone+adlupulone), was obtained from Labor Veritas AG (Zürich, Switzerland). Divinylbenzene/Carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibers and 20 mL SPME vials were purchased from Supelco (Bellefonte, PA, USA). All solvents were of analytical and HPLC-grade.

2,2′-Azino-bis(3-ethylbenzthiazoline-6-sulphonic acid), (ABTS); 2,2-diphenyl-1-picrylhydrazyl hydrate free radical (DPPH^•, 95%); gallic acid (GA, 3,4,5-trihydroxybenzoic acid, 99%); 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox, 97%); and Na₂CO₃ were purchased from Sigma-Aldrich (Steinheim, Germany). Folin–Ciocalteu’s phenol reagent (2 M); 2-(3-hydroxy-6-oxo-xanthen-9-yl)benzoic acid (fluorescein); and 2,2′-azobis-2-methyl-propanimidamide dihydrochloride (AAPH) were from Fluka Analytical (Bornem, Belgium). KCl, NaCl, K₂S₂O₈, and KH₂PO₄ were from Lach-Ner (Brno, Czech Republic). Na₂HPO₄ and isoamyl alcohol (a mixture of isomers) were from Merck KGaA (Darmstadt, Germany). Agricultural origin ethanol (96.3%) was from Stumbras (Kaunas, Lithuania). Liquid nitrogen was from AGA SIA (Riga, Latvia). CO₂ and N₂ gases (99.9%) were from Gaschema (Jonava region, Lithuania). Perchloric acid; 2-thiobarbituric acid; 1,1,3,3 tetraethoxypropane; butylated hydroxytoluene; sulfuric acid; and boric acid were purchased from Sigma-Aldrich Chemie (Steinheim, Germany). Sodium hydroxide (NaOH, 50%) was from Ingle AS (Ingliste, Estonia), and Kjeltabs FOSS Analytical A/S was from Oridor Eesti OÜ (Tartu, Estonia).

Gallic acid (3,4,5-trihydroxybenzoic acid, 99%), 2,2-diphenyl-1-picrylhydrazyl hydrate free radical (DPPH^•, 95%), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox, 97%), Supelco^® 37 Component FAME Mix (10 mg/mL in methylene chloride), microcrystalline cellulose (20 μm), catalytic tablet (3.5 g K₂SO₄ and 0.4 g CuSO₄), Na₂CO₃, were purchased from Sigma-Aldrich (Steinheim, Germany). Folin–Ciocalteu’s phenol reagent (2 M) was obtained from Fluka Analytical (Bornem, Belgium). NaCl, KCl, KH₂PO₄, K₂S₂O₈ were from Lach-Ner (Brno, Czech Republic), Na₂HPO₄ from Merck KGaA (Darmstadt, Germany), boron trifluoride 24% methanol solution from Acros organics (Geel, Belgium), ethanol (96.3%, agricultural origin) from Stumbras (Kaunas, Lithuania), liquid nitrogen from AGA SIA (Riga, Latvia), carbon dioxide and nitrogen gases (99.9%) from Gaschema (Jonava region, Lithuania). All solvents for pressurized liquid extraction (PLE) and solid–liquid extraction (SLE) were of analytical grade. Chromatographic analysis was performed using LC-grade grade solvents.