Milli q iq 7000

N,N′-bis(acryloyl) cystamine (BAC), glutathione (GSH), 2-methoxyethanol (MetCel), phosphate-buffered saline tablets, potassium persulfate (KPS; crystallized from water), poly(vinylpyrrolidone) K90 (PVP), methacryloyl chloride, 1-aminopropan-2-ol, 6-aminohexanoic acid, tert-butyl carbazatem, methyl-6-aminohexanoate, and hydrazine hydrate were purchased from Sigma Aldrich (St. Louis, MO, USA). Poly(vinyl alcohol) 25/140 (PVA) was obtained from Wacker Chemie (München, Germany). 2-Ethoxyethanol (EtCel) and CH₃OH were purchased from VWR (Radnor, PA, USA). Dichloromethane, NaOH, and Na₂CO₃ were purchased from Lachema (Brno, Czech Republic). Tetrahydrofurane was purchased from Lachner (Neratovice, Czech Republic). EDC.HCl was purchased from Gen Script (Piscataway, NJ, USA). For the A4F characterization, the water of MilliQ purity was prepared by laboratory water purification system Milli-Q^® IQ 7000 (Merck KGaA, Darmstadt, Germany), and sodium azide (NaN₃; ≥99%, Lach-Ner, Neratovice, Czech Republic) was used as an antibacterial agent.

Monosodium phosphate (NaH₂PO₄) and disodium hydrogen phosphate (Na₂HPO₄) were purchased from Fisher Scientific (Rodano, Milan, Italy). They were used to prepare 0.1 M phosphate buffer at pH 7.4 with ultrapure water (resistivity = 18.2 M Ω⋅cm) obtained in a Milli-Q^® IQ 7000 water purification system (Merck KGaA, Darmstadt, Germany). Then, the buffer was eluted through a Chelex^® 100 sodium form resin (Bio-Rad, Segrate, Milan, Italy) to remove any metal contamination.
Solutions of DTT and DTNB (5,5′-dithiobis(2-nitrobenzoic acid)) (Sigma Aldrich s.r.l., Milan, Italy) were prepared in phosphate buffer (10 mM), while solutions of L-ascorbic acid sodium salt (AA) (Sigma Aldrich s.r.l., Milan, Italy) were prepared in ultrapure water (10 mM). Aqueous solutions of the reagents were preserved in amber glass vials in the dark at −20 °C, since they are unstable at room temperature and sensitive to light.

All analytical standard solutions were purchased from Cerilliant (Texas, USA) at a concentration of 1.0 mg/mL (native chemicals) or 100 µg/mL (mass-labelled chemicals) in either methanol or acetonitrile. The native chemicals included amphetamine, benzoylecgonine, cocaine, ketamine, mephedrone, methamphetamine, 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxyethylamphetamine (MDEA), methylenedioxymethamphetamine (MDMA), 6-monoacetylmorphine (6-MAM) and norketamine. The corresponding deuterated chemicals included 6-MAM-D₆, amphetamine-D₁₁, benzoylecgonine-D₈, cocaine-D₃, methamphetamine-D₁₁ and MDMA-D₅. The working solution was prepared in methanol at 10 µg/mL for a native-mixture standard and at 1 µg/mL for a mass-labelled-mixture standard (internal standard, IS) stored at −20 °C in amber vials. Ultrapure Milli-Q water was generated from the Milli-Q water purification system (Milli-Q IQ 7000, Merck, Darmstadt, Germany). Concentrated hydrochloric acid (HCl), LC-grade methanol, ammonia solution (32%) and Whatman glass microfiber filters (Grade GF/D) were purchased from Sigma Aldrich. Optima LC–MS grade formic acid was acquired from Fisher Scientific (New Hampshire, USA). Oasis MCX cartridges (150 mg, 6 cc) for solid-phase extraction (SPE) and the SPE manifold with 20 ports were acquired from Waters (Massachusetts, USA).

Ultrapure water (≥18 MΩ-cm resistivity; ≤5 µg L⁻¹ TOC) was obtained from a Milli-Q IQ 7000 purification system (Merck Millipore, Darmstadt, Germany). Elemental calibration solutions for inductively coupled plasma mass spectrometry (ICP-MS) were obtained from HPS (North Charleston, Charleston, SC, USA) and were prepared as 1 g L⁻¹ solutions in 1% nitric acid. All dilutions were performed with analytical-grade 65% nitric acid (Suprapur^®) or 30% hydrochloric acid (Merck, Darmstadt, Germany). Our analytical procedures were validated using the following Certified European Reference Materials (IRMM, Geel, Belgium): “ERM-CC141 Loam soil”, “ERM-CD281 Rye grass”, and “ERM-BD151 Skimmed milk powder”.

The different instruments used in this research were as follows: Zeiss SUPRA 55-VP with a field emission electron gun (FEG), scanning electron microscope (SEM) (Oberkochen, Germany), TGA/DSC 1/1600 (Mettler Toledo, Schwerzenbach, Switzerland), Milli-Q IQ 7000 (Merck, Darmstadt, Germany), Tristar II 3020 (Micromeritics, Norcross, GA, USA), DF-101D magnetic stirrer (Yuhua, Changzhou, China), BY-400C centrifuge (Bai-yang Medical Inst., Beijing, China), Heraeus Vacutherm VT 6060M (Thermo Electron, Langenselbold, Germany), 0.22 µm, 13 mm nylon filter (Bojin, Tianjin, China), HZQ-F160A thermostatic oscillator (Shanghai Yiheng scientific instruments, China), ultrasonic cleaner GT SONIC-D20 (Guangdong, China) and vortex mixture Mix-30S (MIU Instruments, Hangzhou, China).