Ultrapure nitric acid

Elemental analysis was performed for hydrolysed Bio-A proteins. Ashes were determined by weight loss at 105 °C and at 550 °C respectively (Reg.CE 152/2009 IO-CEN); organic matter (OM) by loss in ignition (OM = dry matter–ash); pH in water (3/50, w/v); total carbon (TC) by wet oxidation method with potassium dichromate (MI 1.2.9-Ed.2 Rev.2:2017); total nitrogen (TKN, MI 1.2.9–Ed.2 Rev.2:2017) via the Kjeldhal method; ammonium nitrogen (NH₄⁺ -N) by extraction with diluted HCl and steam distillation with magnesium oxide (UNI EN 15475:2009); total organic nitrogen (TON) by difference (TON = TKN–NH₄⁺ -N). Hydrolysis degree has been calculated following known method (G.U. 26/01/01 n°21, DM 21/12/00). Microbiological stability of the hydrolysed product was evaluated through salmonella (DM 1337 27/01/2014 GU 42 29/02/2014) and coliforms (ISO 4832:2006) content. Total metals were determined by acid digestion with ultrapure nitric acid and hydrogen peroxide (Merck, Darmstadt, Germany) in Teflon bombs in the microwave oven (Milestone, Sorisole, BG, Italy) and determination by Microwave Plasma Atomic Emission Spectrometry (MP_AES, Agilent, Santa Clara, CA, USA). Post-retanned leather samples were examined using a scanning electron microscope (SEM; S-3000 N, Hitachi, Chiyoda, Tokio, Japan) operating at 5 kV.

Filter residues were leached using 0.5 M nitric acid instead of harsh acid digestion that might complicate the results by mineralizing the activated carbon or polypropylene filter material. A known amount (~0.5 gram) of the dried residue (from GAC or PP filters) were mixed with 5 ml of 0.5 M ultrapure nitric acid (Merck) in a beaker and left at room temperature for 24 hours. The mixture following room-temp digestion was filtered through 0.45 µm membrane and diluted to 10 ml with deionized water and saved for ICP-MS analysis as described above.

Mn was assayed in control and Mn-exposed dams immediately following parturition. Rats were sacrificed; and the frontal cortex, neostriatum, and hippocampus were dissected. The kidney, liver, femoral bone, femoral muscle, and heart muscle also were taken as samples. Mn levels were estimated in both control and Mn-exposed rats at P14 and P56. Approximately, 100 mg of each tissue was dissolved in 1.0 ml of ultra-pure nitric acid (Merck). Next, Mn²⁺ content was assayed using SP-2900 Pye Unicam AA (Cambridge, UK) atomic absorption spectrometer and handled according to the Company’s brochure (Whiteside 1976 ). Results were presented in μg/g wet tissue.

A coastal seawater CRM, BCR-579, was provided by the European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM, Geel, Belgium). The certified mercury mass fraction for this material is 1.9 ± 0.5 ng/kg.
Ultrapure water was supplied by the three-step ion exchange system, Milli-Q, fed by the reverse osmosis system, Elix 3, both from Millipore (El Paso, TX, USA). Sixty-five percent of ultrapure nitric acid (Merck KGaA, Darmstadt, Germany) was used for the preparation of acid matrices and cleaning solutions. Sodium tetrahydroborate (proanalysis grade; Merck KGaA, Darmstadt, Germany) and sodium hydroxide from Fluka (Sigma-Aldrich, St. Louis, MO, USA) were used as reductant agents. Sodium chloride for analysis (Merck KGaA, Darmstadt, Germany) was used to prepare artificial seawater matrices. Mercury solutions were prepared by diluting a 1000 mg/L certified solution (Merck KGaA, Darmstadt, Germany).

All samples were taken in May 2022 from the Black Sea. Sampling locations are schematically represented in Figure 3. The studied areas are with different levels of anthropogenic pressure, a bay area vs. a close proximity of a highly urbanized city with notable industries, a large port facility and cover a distance up to 2000 m from the shore. Under flat sea conditions, the collected surface seawater samples were filtered through 0.45 μm polycarbonate membrane filters (Sigma-Aldrich, St. Louis, MO, USA) to remove larger particulate matter, slightly acidified with ultrapure nitric acid (65%, Merck, Germany; to pH 7.5), and placed in acid-cleaned low-density polyethylene bottles (Nalgene General Oceanics, Miami, FL, USA). For preservation, the samples were refrigerated in the dark at 4 °C. Such sample treatment/storage conditions were proven to ensure particle stability prior to analysis [11 (link)]. Used as a field blank, Milli-Q water was stored, treated, and analyzed in the same way as the real samples [6 (link)].

All the reagents (nitric acid), silver nitrate, and silver nanoparticles (colloidal stabled suspension), and 1000 μg/mL standards (Ag and Zn) used for this research work were of p.a. grade, supplied by Merck, Darmstadt, Germany. Ultra-pure nitric acid supplied by Merck, Darmstadt, Germany, and ultrapure water produced by NIROSTA (Millipore, Burlington, MA, USA) were used in ICPMS analysis. Textile samples used for functionalization were pure cotton and viscose materials intended for medical purposes.