N hexane

All reagents were of analytical grade or better. TEXS (toluene; ethylbenzene; o-, m-, and p-xylene; and styrene) were acquired from Sigma-Aldrich (Madrid, Spain, http://www.sigmaaldrich.com). Individual stock standard solutions (1 g·L⁻¹) were prepared in hexane and stored at 4 °C. Working standard solutions were prepared daily by rigorous dilution of the stocks in ultrapure Mill-Q water.
Single-walled carbon nanohorns (SWNHs, >90 wt % purity, 40–50 nm in length and 4–5 nm in diameter) were purchased from Carbonium S.r.l. (Padua, Italy, http://www.carbonium.it/public/site/index.php). SWNHs were dispersed in chloroform (HPLC gradient grade, Sigma-Aldrich, Madrid, Spain) while n-hexane (Panreac, Madrid, Spain) was selected as the eluent.
Tap and Guadalquivir river water samples were selected for the determination of the target compounds following the proposed SWNH-monolithic (micro)solid-phase extraction approach. River waters were collected in amber glass bottles and maintained without headspace at 4 °C until analysis.

Standards 2,3,7,8 TCDD and PCB-1 (2-monochlorobiphenyl), PCB-28 (2,4,4-tri-chlorobiphenyl), PCB-101 (2,2,4,5,5-pentachlorobiphenyl) and PCBs-77 (3,3′,4,5′-tetrachlorobiphenyl), and the organic solvents (AR grade) were purchased from Riedel-de-Haën (Seelze-Hannover, Germany). Pesticide quality solvents (n-hexane and chloroform) were purchased from Panreac (Barcelona, Spain). Chemicals for the synthesis of molecularly imprinted polymers (MIPs), which include, functional monomer methacrylic acids (100 g, 98% purity), porogen solvent chloroform anhydrous (1 L, GC grade 99%), Standard of dioxin (2,3,7,8 TCDD) (1 mL, 97.5% purity) which was used as a template, 1,1′^- Azobis (cylohexanecarbonitrile) (25 g, 98%) used as an initiator, cross linker ethylene glycol dimethacrylate (25 g, 98%), acetic acids (2.5 L, 100%), methanol (1 L, 99.8%), were all purchased from Sigma-Aldrich (St Louis, MO, USA). Nitrogen gas for purge was purchased from AFROX (Johannesburg, South Africa).

In order to determine changes in UV absorbance, a UV-Visible spectrophotometer (UV-2005, J. P. Selecta, Barcelona, Spain) was used. The procedure was the following, based on previous works [50 (link)]: biolubricant samples (1 g) were dissolved in 300 mL of n-hexane (99.0%, PanreacApplichem, Barcelona, Spain). Afterwards, absorbance spectrums were determined within a specific wavenumber range (0–300 nm) for control samples and doped samples (with an optimum TBHQ content, as explained in previous sections) at different oxidation times (0, 1, 3, 5 and 8 h). Thus, the characteristic peak observed during oxidation (at 230 nm, as explained in the Section 2) was selected to observe the changes in absorbance taking place during oxidation.

Organic solvents, such as methanol (high-performance liquid chromatography (HPLC) grade, Carlo Erba, Val de Reuil, France), ethanol (absolute, VWR International, Fontenay-sous-Bois, France), acetone (reagent grade, Sigma-Aldrich, St. Louis, MO, USA), chloroform (VWR International, Fontenay-sous-Bois, France) and diethyl ether (reagent grade, VWR International, Fontenay-sous-Bois, France), were employed for the different extraction procedures. For the assessment of total soluble carbohydrates and polyphenol contents, concentrated sulfuric acid and phenol (reagent grade) were from J.T. Baker (Phillipsburg, NJ, USA), whereas Folin–Ciocalteu reagent, D-glucose, and gallic acid were purchased from Sigma-Aldrich (Milan, Italy). For single polyphenol analysis, commercial standards were supplied by Sigma-Aldrich (Milan, Italy). For the determination of fatty acid composition, n-hexane was purchased from PanReacAppliChem (Barcelona, Spain), whereas fatty acid methyl ester (FAMEs) reference standards (C4-C24) were from Supelco (Bellefonte, PA, USA).

Fatty acid methyl esters (Supelco 35 Component FAME Mix) were obtained from Sigma-Aldrich SL (Madrid, Spain). N-hexane, isopropanol, anhydrous sodium sulfate, undecanoic acid (C11:0), methyl acetate, sodium methoxide, methanol, oxalic acid, and diethyl ether were acquired from Panreac Química SL (Panreac AppliChem, Barcelona, Spain) and Sigma-Aldrich (Merck, Munich, Germany). All reagents were of analytical grade.

Sodium carbonate, sodium chloride, glacial acetic acid, ferric chloride, potassium persulfate, methanol (high-performance liquid chromatography (HPLC) grade), n-hexane (99%, gas chromatography (GC) grade) were obtained from Panreac (Barcelona, Spain). Gallic acid, (±)-6-Hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (TROLOX), Folin–Ciocalteu reagent, 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS); 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,4,6-tris(2-pyridyl) S-Triazine (TPTZ), hexanal, trans-2-heptenal, octanal and trans-2-decenal volatiles standards were acquired from Sigma–Aldrich Inc. (St. Louis, MO, USA). Spring Garlic (Peregrin, Almeria, Spain), Picual virgin olive oil (Tierras de Tavara, Jaen, Spain), onions and crusted pear red tomato jar were obtained in a supermarket in Alicante (Spain) whereas dried thymus and Rosmarinus were acquired from the company Carmencita (Alicante, Spain).

Sodium methylate (0.5 mol L⁻¹ methanolic solution, HPLC grade), sulphuric acid (98%), acetic acid glacial (99.5%), sodium thiosulphate (0.1 mol L⁻¹), starch solution, and n-hexane (99%, GC grade) were obtained from Panreac (Barcelona, Spain). Standards for GC analysis (99%) of methyl tridecanoate, oleic, linoleic, stearic, and palmitic acid methyl esters, petroleum ether (≥95%), methanol (≥99.8%), potassium iodide, chloroform (≥99.8%, for HPLC), acetic acid, hydrochloric acid, isooctane, potassium iodate, p-anisidine reagent, internal standard 4-methyl-2-pentanone, and hexanal (98%) were acquired from Sigma-Aldrich Inc. (St. Louis, MO, USA). All chemicals used were of analytical grade.