Elix milli q academic system

All reagents used were of analytical grade. Ordered mesoporous silica of the SBA-15 type was purchased from ACS Material Advanced Chemical Supplier (Pasadena, CA, USA). (3-aminopropyl) triethoxysilane (APTES, 99%), N- propyl]aniline, toluene (99.8%), acetonitrile ( > 99.9%) were purchased from Sigma Aldrich (Steinheim, DE). Primary Secondary Amine (PSA, Fig. 1 A Hydrochloric acid (35% w/w, d = 1.187 g/mL) and NaOH ( > 98%) were from Carlo Erba (Milano, IT). NaCl, MgSO 4 •7H 2 O and H 2 SO (95-97%, d = 1.84 g/mL) were from Sigma-Aldrich. High-purity water (18.2 M •cm resistivity at 25 °C), produced by an Elix-Milli Q Academic system from Millipore (Vimodrone, MI, Italy), was used for standard and eluent preparation.

Methylene blue (MB) and Rhodamine B (RB), HCOONa and HPLC grade CH3CN used for the eluent preparation were from Sigma-Aldrich (Milan, Italy). Eluent and standard solutions were prepared in high-purity water (18.2 MΩ cm -1 resistivity at 25 °C), produced by an Elix-Milli Q Academic system (Millipore, Vimodrone, MI, Italy).

All chemicals used were of analytical grade or better; 65% HNO3, 40% HF, 37% HCl and 30% H2O2 used for sample mineralization were purchased from Merck or Sigma Aldrich. Standard analyte solutions were prepared by dilution of 1000 mg/L concentrated stock solutions (Merck Titrisol or Sigma Aldrich). Na2CrO4 salt (Sigma-Aldrich) was used for the preparation of Cr(VI) standard solutions. Recovery of water-soluble and precipitated species of Cr(VI) by the extraction solutions was evaluated using Na2CrO4, and PbCrO4 salts respectively. H2SO4 (95-97%) and CH3OH were purchased from Sigma Aldrich (Chemie, Steinheim, DE).
(NH4)2SO4 (Carlo Erba, Arese, Milano, Italy) and NH4OH (Sigma Aldrich) were used for eluent preparation. The post-column reagent, 1,5-diphenyl carbazide (DPC), was from Carlo Erba. The chemicals present in the extracting solutions (see below) were purchased from Sigma Aldrich.
High-purity water (HPW, 18.2 MΩcm resistivity at 25 °C), produced by an Elix-Milli Q Academic system (Millipore, Vimodrone, MI, Italy) was used for the preparation of eluent and standards.
Eluents and sample solutions were filtered through 0.45µm mixed cellulose ester membrane filters.