**2.5 Sensitivity, limit of detection (LOD) and limit of quantitation (LOQ ) calculation for the rGO/MOx nanocomposite**

As shown in **Figure 2(a)** the corresponding calibration curves (−1.0 to +0.8 V) potential range for heavy metal ions (HMIs) simultaneous analysis are recorded for various concentration (1-10 μM). Similarly, the inset of **Figure 2(b)** and **Tables 1** and **2** represent the linearization equations and the corresponding correlation coefficients for rGO/MOx for both individual as well as simultaneous analysis on square wave voltammetry (SWV) or differential normal pulse voltammetry (DNPV).


### **Table 1.**

*Demonstrate the statistical calculation table of limit of detection (LOD) and limit of quantitation (LOQ ) for simultaneous sensing/detection of heavy metal ions (HMIs) using SWV and DNPV voltammetry technique.*


### **Table 2.**

*Statistical calculation of nanocomposites (rGO/MOx) for individual as well as simultaneous analysis of heavy metal ions (HMIs).*

The limit of detection (LOD) and limit of quantitation (LOQ ) for individual as well as simultaneous detection of heavy metal ions (HMIs) via rGO/MOx modified electrodes may be calculated/measured respectively.

The Sensitivity (μA/μM) for individual as well as simultaneous analysis may be calculated. The results gained by the use of rGO/MOx for limit of detection (LOD) and limit of quantitation (LOQ ) both on DNPV and SWV voltammetry analysis may be compared with the World Health Organization (WHO) data for different heavy metal ions (HMIs).

The limit of detection (LOD) and limit of quantitation (LOQ ) of the nanocomposites can be calculated using calibration standards. The limit of detection (LOD) and limit of quantitation (LOQ ) may be determined by 3.3σ/S and 10σ/S respectively, where S is the slope of the calibration curve and σ is the standard deviation of reaction.

The slope can be assessed from the calibration curve of the selection. The estimate of σ is typically the root mean squared error (RMSE) or standard deviation of the residuals taken from the regression line. The slope is used to convert the variation in the response back to the scale of the theoretical concentration.
