Milli q system

The technique was similar to that reported by Grijota et al. [24 (link)]. The method was developed entirely by the research support service of the University of Extremadura using inductively coupled plasma mass spectrometry (ICP-MS) (7900; Agilent Tech., Santa Clara, CA, USA). The linearity of the calibration curves for indium in plasma, serum, urine, erythrocytes, and platelets was greater than 0.985. The equipment was calibrated with several standards prepared from commercial multi element solutions of certified standards.
For plasma, serum and urine samples, the reagents used were nitric acid (HNO₃) 69% Trace select from Fluka and ultrapure water obtained from a Milli-Q system manufactured by Millipore (Burlington, MA, USA). A Rhodium solution of 400 μgL⁻¹ was used as internal standard.
For erythrocyte and platelet samples, the reagents used were 69% HNO₃, hydrogen peroxide, both from Fluka’s Trace Select and ultrapure water obtained from a Milli-Q system manufactured by Millipore (USA). A 400 μg/L Yttrium and Rhodium solution was used as internal standard.
The limits of detection (LOD) and limits of quantification (LOQ) of Fe in the different matrices throughout the investigation were (in μg/L): plasma and serum (LOD = 0.706; LOQ = 7.06), urine (LOD = 0.630; LOQ = 6.30), erythrocytes (LOD = 0.100; LOQ = 1.00) and platelets (LOD = 0.190; LOQ = 1.90).

All chemicals used for the extraction of the phenolic compounds, i.e., methanol and formic acid, were of analytical grade (>99%, Fisher Scientific, Madrid, Spain) and water was obtained from the Milli-Q system (Merck-Millipore, Darmstadt, Germany). For the UHPLC analysis of flavanol glycosides, formic acid and methanol solvents were supplied by Sigma Aldrich (St. Louis, MO, USA) and Milli-Q water was obtained from Milli-Q system (Millipore, Molsheim, France). (+)-Catechin-4′-O-β-glucoside was hemisynthesized as previously described [17 (link)] from (+)-catechin commercial standard supplied by Sigma Chemical Company (St. Louis, MO, USA).

All reagents employed, unless otherwise stated, were of analytical grade. Standards of arbutine, resveratrol, ethyl gallate, syringaldehyde, polydatin, tyrosol, umbelliferon, 4-hydroxybenzoic acid, caffeic acid, chlorogenic acid, gallic acid, homogentisic acid, p-coumaric acid, vanillic acid, ferulic acid, syringic acid, and trans-cinnamic acid were obtained from Sigma-Aldrich (Steinheim, Germany). The structures and CAS numbers of all studied phenolic compounds are summarized in Table 1. Stock standard solutions of all phenolics (ca. 1000 mg/L) were prepared in methanol in amber glass vials. Intermediate working solutions were then prepared by appropriate dilution with Milli-Q water. All stock solutions were stored at 4 °C.
Methanol and acetonitrile (both UHPLC-gradient grade), absolute ethanol and acetone were purchased from Panreac (Barcelona, Spain). Water was purified using an Elix 3 coupled to a Milli-Q system (Millipore, Bedford, MA, USA) and filtered through a 0.22 µm nylon membrane integrated into the Milli-Q system.