Ch3cooh

Deionized water, with medium electrolytic conductivity not exceeding 1 µS/cm at 20 °C, was used for preparing aqueous solutions, along with the following compounds of analytical grade: Pb(NO₃)₂ (POCh, Gliwice, Poland), Zn(NO₃)₂ 6H₂O (POCh), Cd(NO₃)₂ 4H₂O (Acros Organics, Geel, Belgium), Cr(NO₃)₃ 9H₂O (Acros), HNO₃ (POCh), HCl (Chempur, Piekary Slaskie, Poland), H₂SO₄ (POCh), CH₃COOH (POCh), CH₃COONa (Chempur), EDTA-Na (Sigma-Aldrich, Saint Louis, MO, USA) and 2-[4-(2-hydroxyethyl)-1- piperazinyl]-etanosulfonic acid (HEPES, Sigma-Aldrich). The following compounds were used for preparing the membranes: analytical grade trichloromethane (POCh) as the carrier solvent, o-nitrophenyl octyl ether (o-NPOE) and o-nitrophenyl pentyl ether (o-NPPE) with ≥99% purity (Fluka, Busch, Switzerland), bis(2-ethylhexyl) adipate (DOA) with 99% purity (Sigma-Aldrich) as plasticizers, cellulose triacetate (CTA, Fluka) as the polymer support and calixresorcin[4]renes with the structures shown in Figure 1. Synthesis of the carriers was described earlier in the papers [16 (link),17 (link)].
Immobilized supported liquid membranes (SLM) were prepared from 25 µm thick Celgard 2500 type (Hoechst Celanese Corporation, Charlotte, NC, USA) of microfiltration polypropylene membrane sheets, with 45% porosity, pore curvature of 2.22 and pore diameter between 0.04 and 0.4 µm.

All solvents: chloroform, diethyl ether, methanol, and chemicals: CH₃COOH, KOH, NaOH (purchased from Chempur, Piekary Śląskie, Poland), used for extraction and analysis were of analytical grade. Authentic standards of α-amyrin and ursolic acid methyl ester were purchased from Roth (Karlsruhe, Germany); β-amyrin, lupeol, uvaol, oleanolic acid, campesterol, sitosterol and stigmasterol were purchased from Sigma-Aldrich (Steinheim, Germany).