Milli q iq 7000 water purification system

Compritol 888 ATO was a generous gift from Gattefossé (Saint-Priest Cedex, France). Poloxamer 188 and stearic acid were purchased from Alfa Aesar (Ward Hill, MA, USA). Nicotine was procured from Acros Organics (Fair Lawn, NJ, USA). All other chemicals and solvents were of analytical grade and were obtained from Fisher Chemicals (Fair Lawn, NJ, USA). Hydroxypropyl methylcellulose (HPMC) (Methocel^® E4M premium CR (hypromellose USP) (Lot C143851) was purchased from PCCA (Houston, TX, USA). An in-house Milli-Q IQ 7000 water purification system by Merck (Burlington, MA, USA) was used to obtain milli-Q water (resistivity of 18.2 MΩ).

Potassium ferricyanide (K₃Fe(CN)₆), iron(III) chloride (FeCl₃ × 4H₂O), copper(II) sulfate (CuSO₄), Cerium(IV) sulfate tetrahydrate Ce(SO₄)₂ × 4H₂O, palladium chloride (PdCl₃), cobalt(II) chloride (CoCl₂ × 6H₂O), zinc(II) sulfate (ZnSO₄), manganese(II) chloride (MnCl₂ × 4H₂O), cadmium(II) chloride (CdCl₂), neodymium(III) chloride (NdCl₃), 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS), o-dianisidine, hydrogen peroxide (H₂O₂, 30%), sodium ethylenediaminetetraacetate (EDTA), sodium L-lactate, Nafion (5% solution in 90% low-chain aliphatic alcohols) and all other reagents and solvents used in this work were purchased from Sigma-Aldrich (Steinheim, Germany). All reagents were analytical grade and were used without further purification. All solutions used ultra-pure water prepared with the Milli-Q^® IQ 7000 Water Purification system (Merck KGaA, Darmstadt, Germany).

NIPAM (415324), tert-butyl
acrylate (tBA; 327182), 1,6-hexanediol diacrylate (HDDA; 246816),
diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO; 415952), and
disodium hydrogen phosphate (Na₂HPO₄; 71629,
TraceSELECT grade) were purchased from Sigma–Aldrich. Nitric
acid (HNO₃; 6901, ultrapure grade) was purchased from J.T.
Baker. Sodium hydroxide (106466, Suprapur grade) was purchased from
Merck for pH adjustment. All chemical solutions were prepared with
water purified using a Milli-Q IQ 7000 water purification system (Merck
Millipore). Working solutions were prepared via the
serial dilution of multielement calibration standards of Mn(II), Co(II),
Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) (10 mg L^–1; N9300233, PerkinElmer) with 10 mM phosphate buffer. Photocurable
resins of the dual-responsive polymers were prepared by mixing NIPAM,
tBA, HDDA, and TPO (25:56:18:1). TPO was used as the photoinitiator,
NIPAM was used for its stimuli-responsive properties,^{54 (link)−60 (link)} and tBA and HDDA were used for their shape-memory property.^{46 (link),61 (link)}

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 Ωm) obtained in a Milli-Q^® IQ 7000 water purification system (Merck KGaA, Darmstadt, Germany). Next, 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 are unstable at room temperature and sensible to light, thus they were preserved in amber glass vials in the dark at −20 °C.