Hlp 10 system

The serum/saliva samples were dissolved with the acidic treatment in the microwave-assisted digestion system Ethos Up—Advanced Microwave Digestion Labstation (Milestone Srl, Italy) with user-selectable output power (0–1800W with 1W increment). Microwave-assisted acid digestion of samples was performed using a polypropylene rotor equipped with 15 segments with 100 mL capacity, high-pressure Teflon vessels.
The aliquot of 0.25 mL of samples was used for digestion with 3.5 mL of 65% HNO₃ Suprapur® grade and 1.5 mL of deionized water (DI water, conductivity < 0.08 µS/cm, HLP10 system, Hydrolab, Poland) involved the following steps: the temperature increase to 180 °C in 10 min, the target temperature is constant for 15 min, and cooling step was applied for 15 min. The samples were dissolved with (DI) water up to final volume of 7 mL. Solutions were stored at 4 °C prior to Inductively Coupled Plasma Mass Spectrometry (ICP-MS) measurements.

All used chemicals were of analytical grade. CrEL (polyoxyl 35 castor oil, MW = 2500 g⋅mol⁻¹) and phosphate buffered saline (PBS, pH 7.4) were purchased from Sigma Aldrich (Milwaukee, WI, USA). Chl a (MW = 893.5 g⋅mol⁻¹) was isolated from fresh spinach leaves. The detailed protocol is described in [10 ]. PBS solutions were prepared with deionized water (not previously degassed) of conductivity ≤0.06 μS/cm from a HLP 10 system (HydroLab, Straszyn, Poland). Finally, PBS solutions for each experiment were filtered through a set of membrane filters (Millipore Express Plus, 0.22 μm). The concentration of dissolved oxygen in aqueous solutions was recorded using a HI-2004 Edge^® Dissolved Oxygen Meter with a HI 764080 electrode (Hanna Instruments, Woonsocket, RI, USA). All samples were prepared and stored in brown glass vials with screw caps (Thermo Fisher Scientific, San Jose, CA, USA).

Nitrolite was obtained from Purolite International, Ltd.,UK. Nitrolite was washed prior to the experiments in order to remove the surface dust. The physicochemical characteristics are presented in Table 1 [16 (link)].
Then, the sorbent was washed with demineralized water and dried at room temperature. The La(III), Ce(III), Pr(III), Nd(III), Cr(III) solutions were prepared form ROMIL PrimAg^® Mono-Component Reference Solutions. The metal ion solutions were in the nitrate form, being prepared from nitrate salts. The water used for investigation was HPLC grade and was obtained from the Hydrolab HLP 10 system. Its conductivity was 0.1 uS/cm. The pH values were adjusted by using sodium hydroxide and nitric acid solutions.