# Application of Microgel as a Sorbent for Bisphenol Analysis in Liquid Food Samples
## 3 Results
### Comparison of Microgel with SPE Cartridges  
Both SPE procedures for Supelclean(tm) ENVI-18 and Affinimip(r) cartridges were taken from the producer's application notes with slight modifications (Table 3). The suggested cleaning mixture has a higher concentration of organic solvent, which throughout the extraction procedure resulted in eluting bisphenols from the sorbent of both cartridges. This is why the cleaning mixture was changed to 5/95 ACN/H\({}_{2}\)O. The amount of 10 mL of filtered extract from fruits in syrup (without dilution) was spiked with 50 ug\(\cdot\)L\({}^{-1}\) standard solution of BPB, BPE, BPF and BPA, and then it was introduced into the SPE cartridge. Following the application of the extract, cartridges were washed with 5 mL of 5/95 acetonitrile/water mixture, and each sample was eluted with 2 mL of 80% of methanol/water mixture. The experiments for microgel were performed in 2 mL microcentrifuge tubes; for that reason, the amount of the loading sample and elution solvent must be smaller in comparison to SPE cartridges. After preconcentration, all collected samples were analyzed by LC-FLD, and recoveries were calculated.  
As presented in Figure 5, both cartridges showed very good recoveries (101.3-115.6% for Affinimip(r) and 98.5-112.8% for Supelclean(tm) ENVI-18) for preconcentration of 10 mL of fruits in syrup spiked with 50 ug\(\cdot\)L\({}^{-1}\) standard solution of investigated bisphenols. However, the Supelclean(tm) ENVI-18 cartridge was easily clogged with the matrix of the food sample, which prolonged the SPE procedure. The recoveries obtained for our microgel SPE procedure were comparable (from 71.2 to 108.3% for all bisphenols). However, lower recoveries (71.2-72.4%) obtained for BPE and BPF were caused by weaker retention of both bisphenols on microgel as small amounts were found in the effluent. In order to verify the results obtained on the microgel, all the samples where BPA was found (mandarin, pineapple, mushroom, peach and pickles) were also preconcentrated by using Affinimip(r) cartridge, and the results were consistent with each other. For example, by using Affinimip(r) cartridge for preconcentration, the determined amount of BPA in pickles was 10.9 ug\(\cdot\)L\({}^{-1}\) and 19.8 ug\(\cdot\)L\({}^{-1}\) for peach. These results differ only by less than 10% to the concentrations determined after microgel extraction (Table 2).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Analyte**} & **Pineapple** & **Mandarin** & **Mushroom** & **Peach** & **Pickles** \\ \cline{2-6}  & & & **C** [ug\(\cdot\)L\({}^{-1}\)] & & \\ \hline BPA & 6.2 \(\pm\) 0.9 & 8.5 \(\pm\) 0.4 & 11 \(\pm\) 0.4 & 22 \(\pm\) 2.0 & 12 \(\pm\) 1.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The detected concentration of bisphenol A in liquid food samples after the extraction procedure.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sorbent** & **Microgel (5 mg)** & **ENVI-18 (500 mg)** & **Affinimip® (100 mg)** \\ \hline \multirow{3}{*}{Conditioning} & \multirow{3}{*}{-} & 5 mL of MeOH 1  & 3 mL of 2\% FA 2/MeOH \\  & & 5 mL of H\({}_{2}\)O & 3 mL ACN 3  \\  & & 1 mL of fruits in syrup & 10 mL of fruits in syrup & 10 mL of fruits in syrup \\  & spiked with 50 ug\(\cdot\)L\({}^{-1}\) & spiked with 50 ug\(\cdot\)L\({}^{-1}\) & spiked with 50 ug\(\cdot\)L\({}^{-1}\) \\ \hline Cleaning & 0.5 mL of H\({}_{2}\)O & 5 mL of 5/95 ACN/H\({}_{2}\)O & 5 mL of 5/95 ACN/H\({}_{2}\)O \\ \hline Elution & 0.2 mL of 80\% MeOH & 2 mL of 80\% MeOH & 2 mL of 80\% MeOH \\ \hline \hline \end{tabular}
\end{table}
Table 3: Solid-phase extraction methods used for preconcentration of fruits in syrup.