**1. Introduction**

Polyaniline (PANI) is one of the best known conductive polymers with broad application in many fields such as chemistry, physics, optics, materials and biomedical science. It was applied, e.g., as a component of sensors, diodes, solar batteries, electromagnetic shields, and materials for protection against corrosion [1–5]. Due to the unique properties of PANI such as simplicity of synthesis, mechanical and chemical flexibility, resistance on pH and temperature, hydrophobicity, π-conjugated structure, polar groups, and ion exchange ability [1,2,6,7], it also proved to be useful in extraction techniques, mainly as a component of various composites, e.g., with graphene [8], montmorillonite [9], cyclodextrin [10], polyester [11], etc. Metal fibers covered with these types of materials were used for

solid-phase microextraction (SPME), magnetic solid phase extraction (MSPE), headspace solid phase microextraction (HS-SPME) and magnetic dispersive solid phase extraction (MDSPE) of different target compounds from the matrix. Polyaniline and sorbents modified with PANI were also successfully applied in solid phase extraction (SPE) [12–18]. However, reports on the applications of polyaniline based materials for plant samples are scarce. For instance, Arnnok et al. [19] used polyaniline-modified zeolite in DSPE of fruit and vegetables to isolate carbamate, organophosphate, sulfonylurea, pyrethroid and neonicotinoid; Alizadeh et al. [11] adapted polyester-polyaniline fiber for SPME of volatile organic compounds (VOCs) from lemon juice, and silica modified with polyaniline (Si-PANI) was applied as an SPE adsorbent for sample clean-up before HPLC analysis of triterpenes in plant extracts [18]. SPE is one of the most common techniques for pretreatment of biological materials; however, it has some drawbacks, e.g., the relatively time-consuming procedure, the high consumption of solvent, and the risk of losses of volatile analytes [20–22]. Therefore, recently, the other techniques have gained attention of researchers dispersive solid phase extraction (d-SPE) and matrix solid–phase extraction (MSPD). Both techniques are useful for pretreatment of samples with complex matrix, due to high efficiency combined with low cost, simplicity and high speed of process [23–27].

In the present study, Si-PANI was tested as a sorbent for d-SPE and MSPD of oleanolic, ursolic and betulinic acid from *Viscum album* L. and *Ocimum basilicum* L. Polyaniline was chosen for covering of silica because the mix mode retention mechanism allows to retain various group of analytes, both charged and uncharged, cationic and anionic forms. The extraction conditions such as: form of PANI, washing solution and eluent were optimized experimentally. The physico-chemical features of the sorbent such as polyaniline form and quality the deposition of PANI film on silica were verified by Raman spectroscopy and microscopy combined with automated procedure using computer image analysis.

### **2. Methods and Materials**

### *2.1. Materials and Reagents*

Silica gel Lichrospher 60 Si, aniline (for analysis EMSURE), ammonium peroxydisulphate (extra pure) used for synthesis of the adsorbent, solvents and reagents: ammonia solution, hydrochloric acid, ortho-phosphoric acid, ammonium acetate, methanol, acetonitrile (gradient grade for liquid chromatography) were from Merck (Darmstadt, Germany). Water was deionized using ULTRAPURE Milipore Direct-Q® 3UV–R (Merck). Standards of betulinic (BA) ( ≥98%), oleanolic (OA) ( ≥97%), and ursolic (UA) ( ≥98.5%) acid were purchased from Sigma-Aldrich (St. Louis, MO, USA).

Extracts from *Viscum album* L. and *Ocimum basilicum* L were prepared by extraction of pulverized plant material (1.00 g) with methanol (2 × 20 mL) in ultrasonic bath (2 × 15 min). The obtained extracts were concentrated to 10 mL and filtered through Millex Samplicity Filters 0.20 μm (Merck).
