## 4 Results and Discussions  
Voltammetric behavior of C- and Pt-electrodes in the absence of an electroactive substance was described earlier [15]. In Reference [15], we gave the results of decoding a voltammetric series with the help of the DGI method. In the practical aspect, it is interesting to compare the results presented in this paper with results obtained earlier. The special interest is related to parameters calculated for the integral voltammetric curves. In the presence/absence of electroactive substance in the repeated sensor, the integral curves allow obtaining more monotone parameters in data space, which reflects the modification of the sensor surface and variations of the solution content at small variations of the electroactive component's concentration. It is interesting to note that the results obtained earlier for the background solution allow quantitatively characterizing the aging phenomenon;  
Figure 7: (**a**) Monotone behavior of the statistical parameters \(\sigma_{B}\)(c) and \(\sigma_{C}\)(c) in data space that can be chosen for calibration purposes. They independently confirm the behavior of the ellipse rotation (correlation) angle (see Figure 6) found for the discrete geometrical invariants (DGI) of the second order. (**b**) Random-like (non-monotone) behavior of the statistical parameters \(\sigma_{B}\)(c) and \(\sigma_{C}\)(c) in the measurement space for the C-electrode, which cannot be chosen for calibration purposes. They reflect the strong fluctuation characteristic of the measurement space, confirmed also by the parameters characterizing the invariant of the second order. As for the Pt-electrodes, these curves demonstrate quasi-monotone behavior. the repeated cycles of electrochemical oxidation/reduction of the components of the background electrolyte are accompanied by surface electrode degradation. This phenomenon was observed for C- and Pt-electrodes. In voltammetry, there is a signal drift problem and a sensor memory effect tightly related to it. The elimination of this negative effect is impossible, especially for cases where a large number of electrodes are used to form the given multisensor system. One solution is to use special mathematical methods for a quantitative description of the random noises and signal drifts aggravated by the measured equipment interferences. Comparing the preliminary results obtained earlier in Reference [15], one can formulate the following conclusions:  
1. The C- and Pt-electrodes at the repeated functioning cycles exhibit the aging phenomenon that leads, in turn, to the temporal signal drift. This drift distorts the measured VAGs. This effect is expressed clearly in the analysis of the curves associated with the measurement space. For a quantitative description, as well as the control and elimination of this negative phenomenon, we use the DGI method that frees the system from the imposed model and errors related to the treatment procedure. 2. The integral curves in the measurement space because of the DGI application demonstrate the sensitivity of both electrodes to the amino-acid concentration variations (see the monotone curves obtained for the data space). 3. The aging effect confirms our previous conclusions; after achieving the activated state, the electrode behavior at the given potential sweep depends on the number of cycles to a lesser degree. This effect is expressed clearly for the more inertial Pt-electrodes. For C-electrodes, we presumably observe the varied behavior covering all 1000 measurements. 4. The ratio Rt(_c_) = <y(_c_)>/ <x> (remember that the variable <x> = <y(0)> is always related to the buffer solution), while dispersion Dsp(_c_) = <DY^2>/ <DX^2>, depicted in Figure 4a, characterizes the center of gravity and its standard deviation. They are more sensitive to the surface changes evoked by the aging phenomenon. Both parameters have monotone behavior for C- and Pt-electrodes in the presence/absence of the amino acid.