# Electrochemically Activated Screen-Printed Carbon Electrode for Determination of Ibuprofen
## 3 Results and Discussion
### Analytical Characteristic (LOD, LOQ, Repeatability, Reproducibility and Selectivity)  
In our earlier work, we found that the electrochemical activation of the electrode surface using CV in 0.1 M NaOH resulted in changes in its morphology and a decrease in the charge transfer resistance, which translated into a significant increase in the rifampicin oxidation peak current [15]. Based on these conclusions, under optimized conditions the DPV measurements were made to two IBP calibration curves, at the non-activated electrode (SPCE) and electrochemically activated using CV in 0.1 M NaOH electrode (aSPCE). As shown in Figure 4A,C, with the increase of IBP concentrations, the DPV oxidation peaks increased gradually. As can be seen, the linear ranges of calibration curve obtained at the SPCE were from 5.0-50.0 and 50.0-500.0 \(\rm\upmu M\). Moreover, the results demonstrated that the anodic peak currents were proportional to two ranges of IBP concentration intervals (Figure 4D), one is 0.5-20.0 \(\rm\upmu M\) (r = 0.9988) and the other is 20.0-500.0 \(\rm\upmu M\) (r = 0.9992) at the aSPCE. The limits of detection (LOD) and quantification (LOQ) were 1.50 and 5.0 \(\rm\upmu M\) (for SPCE), and 0.059 and 0.20 \(\rm\upmu M\) (for aSPCE), respectively (LOD = 35 Da/b;  
Figure 2: Effect of \(\rm pH\) (**A**) and acetate buffer concentration (**B**) on the analytical signal of 20.0 \(\rm\upmu M\) IBP.  
LOQ = 10 SDa/b, SDa--standard deviation of intercept (_n_ = 3); b--slope of calibration curve) [17]. The results confirmed that the electrochemical activation by CV in 0.1 M NaOH surface of screen-printed electrode contributes to the enhancement of analytical signals and thus to lowering the LOD and LOQ of IBP. Moreover, compared with the aSPCE and SPCE, the oxidation peak shifted towards less positive potential at the aSPCE. As can be seen, the LOD is significantly lower than those obtained for another methods and electrodes. It should be emphasized that the SPCE activation procedure was performed only once before all DPV measurements for the one IBP calibration curve. So the SPCE surface should be electrochemically activated before replacing the IBP solution.  
A comparison between the analytical performance of the present activated sensor and other methods as well as some previous literature electrodes for the determination of IBP in pharmaceutical formulations is given in Table 1.  
For validation of the proposed analytical procedure, IBP signal repeatability, reproducibility of electrode-to-electrode and selectivity of method were evaluated. The repeatability was examined by the determination of 20.0 uM at the aSPCE for ten successive measurements. The relative standard deviation (RSD) of the result was 3.5% (_n_ = 10), indicating that the IBP at the aSPCE has good repeatability. Moreover, under the same procedure, three aSPCE were prepared independently and the reproducibility was estimated. The RSD was 4.5% (_n_ = 9) for the peak current measured for 20.0 uM IBP, which demonstrates the reliability of the electrochemical activation procedure.  
Next, the effect of potential interferents occurring in pharmaceutical formulations on the IBP signal (20.0 uM) was studied. It was found that the IBP signals are stable (up to \(\pm\)10%) for the 50-fold excess of glucose and paracetamol.