2.2.2. Performing of HPLC Analyses

Qualitative and quantitative analyses by high-performance liquid chromatography (HPLC—VWR/Hitachi LaChrom Elite®, Tokyo, Japan) on the release of p-AA from the respective (homo)- and (co)oligoesters were performed. The samples were filtered through syringe filters Iso-Disc™ (0.2 μm, Supelco®) (Sigma-Aldrich Chemie GmbH, Steinheim, Germany) and separated on a LiChrospher® RP-18 column (250 mm <sup>×</sup> 4 mm, 5 <sup>μ</sup>m, Merck) protected by guard column LiChrospher® RP-18 (4 mm × 4 mm, 5 μm, Merck KGaA, Darmstadt, Germany). The mobile phase consisted of 0.1% formic acid in water and acetonitrile. Table 1 shows the solvent gradient used for separation. The flow rate was set at 1 mL/min. The evaluation was performed using diode array detector (DAD) at 254 nm. The samples were analyzed in triplicate. The standard curve of peak area versus acid concentration was constructed over the range from 0.03 to 125 μg/mL and subjected to linear regression analysis (R2 = 0.9953). The calibration curve used for HPLC measurements is presented in Figure 1.


**Table 1.** Solvent gradient used for high-performance liquid chromatography (HPLC) analysis.

A is 0.1% formic acid in water and B is acetonitrile.

**Figure 1.** High-performance liquid chromatography (HPLC) calibration curve for p-anisic acid.

*2.3. Assessment of Cytocompatibility of (Homo) and (Co)oligoesters Containing the p-Anisic Acid Moiety*

#### 2.3.1. Statistical Analysis

The data were analyzed by use of a one-way analysis of variance (ANOVA) followed by a Tukey post hoc test. All of the obtained results were expressed as means ± SD. *p*-value of <0.05 was considered statistically significant. The analysis was performed with a use of Statistica 13.3 software (StatSoft, Kraków, Poland).
