Lc ms grade water

The reference compounds 3,4-dihydroxycinnamic acid, chlorogenic acid, 4-hydroxy-3-methoxycinnamic acid, 4′-hydroxycinnamic acid, 3,4,5-trihydroxycinnamic acid, 4-hydroxybenzoic acid, (−-epicatechin, apigenin, cyanidin-3-glucoside, (±)-6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox), and β-carotene, and the individual sugars glucose, fructose, and sucrose, were obtained from Sigma-Aldrich (Steinheim, Germany). Formic acid was obtained from Sigma-Aldrich. LC-MS grade water, methanol, ethanol, dichloromethane, and acetonitrile were acquired from PanReac Applichem (Castellar del Vallés, Barcelona, Spain).
Note: the names for the phenolic compounds used in this paper are based on the nomenclature thesaurus of Kay et al., 2020 [16 (link)].
The reagents 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl (DPPH), 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AAPH), fluorescein, potassium persulfate, sodium hydroxyde, potassium dihydrogen phosphate, and sodium hydrogen phosphate were also acquired from Sigma-Aldrich (Steinheim, Germany).

LC–MS-grade methanol (from Honeywell) was used for extractions (including SPE cartridges preconditioning) and analyses. LC–MS-grade water (from PanReac Applichem) was used for HPLC–MS analyses and SPE cartridges preconditioning or washing. Ammonium acetate (from Aldrich) was used as an additive for HPLC eluents. Perfluorooctanoic acid analytical standard (> 98% from Aldrich) was used for LC–MS calibration curves and to obtain spiking solutions which were freshly prepared and checked for their PFOA content before each batch of analyses. SPE cartridges Strata TM-X-AW (33-µm polymeric weak anion 200 mg/6 mL tubes) were purchased from Phenomenex and used for PFOA extraction from seawater samples. PFOA-free polypropylene micropipette tips were used for quantitative small volume withdrawals. In order to prevent any type of PFOA contamination, the equipment used for sampling and extraction procedures was washed with the same methanol used for extraction and analysis. LC–MS analyses were performed using a 6540 UHD Accurate-Mass Q-TOF LC/MS (Agilent Technologies) equipped with a Dual AJS ESI source. Histograms, tabs, and statistical analysis have been realised using Excel 2016 (Microsoft) and PAST3 (Hammer et al. 2001 ).

Methanol of LC-MS purity grade (from Honeywell, Charlotte, NC, USA) was utilized for extractions and analyses. LC-MS grade water (from PanReac AppliChem, Chicago, IL, USA) was used for HPLC-MS analyses preconditioning or washing procedures. Ammonium acetate (from Aldrich, St. Louis, MO, USA) served as an additive for HPLC eluents during analyses. Sodium sulfate, purchased from Aldrich, was used in the filtration process. The analytical standard of perfluorooctanoic acid (PFOA), with a purity grade exceeding 98% and acquired from Aldrich, was employed for LC-MS calibration curves and for preparing spiking solutions. PFOA-free polypropylene micropipette tips were used for small-volume withdrawals to prevent any PFOA contamination. The equipment used for sampling and extraction procedures was thoroughly washed with methanol to avoid contamination. LC-MS analyses were conducted using a 6540 UHD Accurate-Mass Q-TOF LC-MS/MS system (Agilent Technologies, Santa Clara, CA, USA) equipped with an Electron Spray Ionization source type Dual AJS ESI, operating in negative ionization mode.