Optima 8000 spectrometer

Approximately 100 mg of shoot or root dry biomass was carefully weighed and mineralized in a microwave medium pressure digestor (Milestone Start D, FKV Srl, Torre Boldone, Italy) with 7 mL of 69% HNO₃ and 2 mL of 30% H₂O₂ (ultrapure grade). Zinc concentration in the resulting solutions was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) using an Optima 8000 spectrometer (Perkin Elmer, Waltham, MA, USA), following the procedure of [83 ].

Cellular uptake of TiO₂ NPs was determined by measuring intracellular titanium concentration using inductively coupled plasma-optical emission spectrometry (ICP-OES). Briefly, 2 × 10⁵ cells/well were seeded in culture dishes. After adhesion, cells were exposed to TiO₂ NPs (0, 25 and 100 μg/mL) under normal gravity and simulated microgravity. After 48 h, cells were washed with PBS, and collected by trypsinization. Cell count was conducted using trypan blue staining. Then cells were suspended in 100 μL PBS and stored at 4 °C until digestion. Samples were transferred to a quartz beaker, then 3 mL of ultrapure HNO₃ was added and the samples were heated for 2 h at 120 °C. Afterwards, 1 mL H₂O₂ was added for further heating digestion, and then the samples were dried by heating at 180 °C. Next, the obtained solutions (about 200 μL) were transferred to a polypropylene vessel and diluted to 3 mL with 2% HNO₃. A calibration curve was constructed using standard solutions prepared by serial dilution of a reference solution (NIM-RM3041, National Institute of Metrology, 100 mg/L) and intracellular Ti concentrations of the samples were measured with a Optima 8000 spectrometer (PerkinElmer, Waltham, MA, USA). Cellular uptake of TiO₂ NPs was calculated against the cell counts (µg/10⁵ cells).

ICP-MS Nexion 350X with an ESI autosampler (Perkin Elmer, USA instrument, Perkin Elmer, Waltham, Massachusetts, MA, USA) was used to determine total cerium concentration in the receiver phases. A six-point standard curve obtained by the dilution of cerium standard solution for ICP-MS analysis (by Sigma Aldrich, Milan) was used for ICP-MS measurements (0.01–10 μg L⁻¹, ion mass 140 u.m.a.). The limit of detection of cerium was 0.001 μg L⁻¹ for ICP-MS and the precision of the measurements as repeatability (relative standard deviation (RSD) %) for the analysis was <5%.
Total cerium concentration in donor phases and in the solutions resulting from the mineralization of the skin samples were performed by (ICP-OES) using an Optima 8000 Spectrometer (PerkinElmer) equipped with an S10 Autosampler. ICP-OES analyses were conducted using a calibration curve obtained by dilution (range: 0–10 mg L⁻¹) of cerium standard solution (by Sigma Aldrich, Milan, Italy). The limit of detection (LOD) at the operative wavelength of 413.764 nm was 0.01 mg L⁻¹. The precision of the measurements expressed as RSD % for the analysis was always less than 5%.