## 4 Results and Discussions
For the Pt-electrode, this monotone dependence is weak; it confirms the high stability of the Pt-electrode during electro oxidation processes. We should stress here that Figure 4a,b are more informative and allow characterizing the d-tryptophan behavior, as well as comparing its electroactivity with the interaction of C- and Pt-electrodes. 1. In data space, the dispersion curves Dsp for C- and Pt-electrodes differ by their mutual location with respect to each other; the value Dsp(_c_) (C-electrode) exceeds the curve Dsp(_c_) (Pt-electrode) for all values of \(c\). The gravity ratios Rt(_c_) for both types of electrodes are strongly deviated from each other as well. 2. In measurement space, a significant difference is observed for the curve Dsp(c) (Pt). It is explained by the excess electroactivity of the tryptophan molecule in its interaction with the Pt-electrode. One can stress here that the clearly expressed peaks on the initial VAGs were not observed. Therefore, one can conclude that parameters Rt(_c_) and DSp(_c_) contain qualitative information about the nature of the depolarizator and the corresponding electrode. 5. The behavior of parameters _A_(c) and _B_(c) (Figure 5a,b) is more sensitive to the surface changes; the behavior of parameter _A_(_c_) for both types of electrodes is characterized by a monotone behavior, which increases in the presence/absence of the amino acid. 6. The ellipse rotation (correlation) angle \(\alpha\) for the C-electrode in the absence of amino acid does not correlate with the number of oxidation/reduction cycles; furthermore, it does not depend on the sensor duration and cannot be associated with the aging phenomenon. However, as shown in Figure 6, this parameter correlates strongly with d-tryptophan concentration. The calculated curve is monotone with respect to increasing the concentration of d-tryptophan. For the Pt-electrode after 300 cycles in the presence/absence of amino acid, this curve has an increasing trend. We relate this increasing tendency with additional processes of oxidation in the background solution. From our point of view, this parameter can be used for calibration purposes of some non-electroactive components of the background solute. 7. The parameters analyzed above reflect the specificity of electrode processes from different points of view. For the more active C-electrode, which has better oxidation characteristics, many output DGI parameters changed more intensively in comparison with the more inertial Pt-electrode. The Pt-electrode is more stable in oxidation processes. Being a more \"stable\" material with respect to the transfer electron process related to the oxidation of amino acids, it requires the calculation of an extended set of \"fine\" parameters that are sensitive to concentration variations of the electroactive substance. For the given case, we associate these variations with the behavior of parameter \(\sigma_{B,C}\). As it follows from the analysis of Figure 7a, these parameters have monotone and decreasing characteristics against the concentration in data space. In the measurement space shown in Figure 7b, these parameters characterize again the electroactivity of the C-electrode, which has variable characteristics, compared to the relatively stable behavior of the Pt-electrode. Again, the 300-cycle boundary is conserved. Only after this limit does the Pt-electrode tend to the aging regime. 8. The proposed DGI approach is rather general and enables comparing random curves with different samples, using the _same_ set of parameters expressed in terms of moments up to the fourth order. We showed also that these parameters have different sensitivity with respect to the input factor (in our case, this factor is associated with concentration of the amino acid).