2.2.2. Extraction Experiments

Optimisation of extraction procedure was conducted using a methanolic standard solution of oleanolic (OA), betulinic (BA) and ursolic acid (UA) at concentration of 0.1 mg/mL. All the experiments were performed in triplicate at ambient temperature.

### Dispersive Solid Phase Extraction (d-SPE)

OA, UA and BA solution (1 mL) was mixed with various amounts of sorbent (100, 150, 200 and 250 mg), degassed, and dynamically shaken using vortex for 1–10 min. The suspension was subsequently centrifuged at 9000 rpm for 5 min, supernatant was removed and analyzed with the use of HPLC. The amount of retained compounds was calculated as a difference between applied amount and amount found in supernatant.

The analytes were eluted by shaking with 3 mL portions of various solvents, supernatants were filtered, analyzed with the use of HPLC and % of recovery was calculated.

Finally, the optimized d-SPE conditions were applied for sample pretreatment of plant extracts.

### 2.2.3. Matrix Solid Phase Dispersion (MSPD)

Pulverized plant material was mixed with Si-PANI, ground to powder (ca. 5 min), packed into a 3-mL polypropylene column, and retained by two polyethylene frits. Eluent was passed through the column using Millipore vacuum pump system (Merck) at the flow rate of 1 mL/min and the eluates were analyzed by HPLC.
