## 3 Results and Discussion
### Effect Concentration Ratios and Evaluation Methods on Analytical Performance  
In general, peak height and width increase with a higher concentration of analyte. It follows that concentration ratio can significantly distort the recognition of individual ocopherols. Hence, it was necessary to find out if investigated ocopherol compounds overlap within the scope of calibration measurement, which could affect the main analytical characteristics, namely linear range, limit of detection (LOD), limit of quantification (LOQ), precision, and accuracy. Figure 4A-C represents calibration voltammograms (20-200 \(\mu\)mol L\({}^{-1}\)) of a selected form of ocopherols, whereas two others had a constant concentration of 50 \(\mu\)mol L\({}^{-1}\). Additionally, calibration measurements were performed to find out mutual influencing, where the concentration of two forms was simultaneously increased, as shown in Figure 4D-F. Resultant voltammograms showed that overlapping of \(\gamma\)-TOH and \(\delta\)-TOH anodic peaks is more evident if one of these forms has a higher concentration than the other, whereas the mutual recognition of \(\alpha\)-TOH and \(\delta\)-TOH peaks increased with a higher concentration of both forms. Surprisingly, the overlapping was suppressed if concentrations of all three forms (3-300 \(\mu\)mol L\({}^{-1}\)) were mutually increased (see Figure 4G). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Electrode** & **Method** & **Working Medium** & \multicolumn{3}{c}{**Anodic Peak Potential (V)**} \\  & & & \(\alpha\)**-TOH** & \(\gamma\)**-TOH** & \(\delta\)**-TOH** & **Reference** \\ \hline GCPE & ExSV-SWV & H\({}_{2}\)O and acetone (40:60) & 0.475 & 0.520 & 0.540 & [12] \\ GCE & DPV & Benzene and MeOH (1:2) & 0.644 & 0.714 & 0.804 & [19] \\ GCE & DPV & Hexane and EtOH (40:60) & 0.475 & 0.550 & 0.665 & [23] \\ PtE & DPV & Glacial acetic acid & 0.692 & 0.755 & 0.889 & [24] \\ GCE & SWV & MeCN & 0.645 & 0.753 & 0.857 & This work \\ \hline \hline \end{tabular} Notes: GCPE; glassy carbon paste electrode and ExSV; extractive stripping voltammetry.  
\end{table} 
Table 1: Comparison of electrode material and working medium on anodic potential peaks. Overview of all analytical parameters obtained during simultaneous voltammetric detection of investigated tocopherols is presented in Table 2. To achieve the coefficient of determination (\(R^{2}\)) in the accepted value higher than 0.9900, calibration ranges from 3 to 100 \(\mu\)mol L\({}^{-1}\) for all tocopherol forms can be taken into account. High positive y-intercept (\(q\)) values and low sensitivity (\(k\)) of appropriate equations of the calibration curves (\(q>0.2\)\(\mu\)A and \(k<0.09\)\(\mu\)A mol\({}^{-1}\) L) were obtained when polynomial, linear curve cursor, and zero base evaluation methods were used. On the other hand, if the deconvolution evaluation method is preferred, values of \(q<0.1\)\(\mu\)A and \(k>1.0\)\(\mu\)A mol\({}^{-1}\) L will be obtained. Therefore, the deconvolution should be preferred. From all LOQ values shown in Table 2, it seems that the present study could help to develop a simple voltammetric determination of the \(R^{2}\) values. Figure 4: SWVs of 20–200 \(\mu\)mol L\({}^{-1}\) of one tocopherol form when two others had a constant concentration of 50 \(\mu\)mol L\({}^{-1}\) (varying \(\alpha\) concentrations); (**A**), varying \(\gamma\) concentrations; (**B**) and varying \(\delta\); (**C**). SWVs of 20–200 \(\mu\)mol L\({}^{-1}\) of two tocopherols when one had a constant concentration of 50 \(\mu\)mol L\({}^{-1}\) (varying \(\gamma\) and \(\delta\) concentrations); (**D**) varying \(\alpha\) and \(\delta\) concentrations; (**E**) and varying \(\alpha\) and \(\gamma\) concentrations;(**F**). Simultaneous voltamactic detection of 3–300 \(\mu\)mol L\({}^{-1}\) of all tocopherol forms (**G**). All voltammograms were obtained at GCE in pure MeCN containing 0.1 mol L\({}^{-1}\)LiClO\({}_{4}\), \(E_{\rm step}\) = 1 mV, \(E_{\rm ampl}\) = 25 mV, and \(f\) = 25 Hz.