In some electrochemistry research papers, the result obtained from a differential pulse voltammetry (DPV) technique is presented in peak current vs. log(concentration) plot. in such cases, how to calculate sensitivity, LoD and LoQ from that data? Also what about their "unit"?
To calculate sensitivity, Limit of Detection (LoD), and Limit of Quantification (LoQ) from a Differential Pulse Voltammetry (DPV) plot of peak current against the logarithm of concentration, you typically need to perform a series of steps:
Plot the DPV Data: Plot the peak current (y-axis) against the logarithm of concentration (x-axis) for your analyte.
Determine Sensitivity: Sensitivity is typically calculated as the slope of the linear portion of the calibration curve. You can determine this by fitting a linear regression line to the data points in the linear range of the plot. The slope of this line represents the sensitivity of the method.
Calculate LoD: LoD is often defined as the concentration that yields a signal-to-noise ratio (S/N) of 3:1. To calculate LoD, you need to estimate the noise level from the baseline of the DPV plot. Then, using the formula: LoD = 3 * (Standard Deviation of Blank / Sensitivity), you can determine the concentration corresponding to the 3:1 S/N ratio.
Calculate LoQ: LoQ is typically defined as the concentration that yields a signal-to-noise ratio (S/N) of 10:1. Similar to LoD, you estimate the noise level from the baseline of the DPV plot and then use the formula: LoQ = 10 * (Standard Deviation of Blank / Sensitivity) to determine the concentration corresponding to the 10:1 S/N ratio.
You can calculate sensitivity, Limit of Detection (LoD), and Limit of Quantification (LoQ) from a DPV plot of peak current vs. logarithm of concentration using the following steps:
1. Perform a linear regression analysis:
- You'll need your peak current data (y-axis) and the corresponding logarithmic concentration values (x-axis) for this step.
- Use linear regression analysis to fit a straight line to your data points.
- The linear regression analysis will provide you with the slope (m) and the y-intercept (b) of the equation that best fits your data. The slope (m) represents the sensitivity of your DPV measurement.
2. Calculate the standard deviation of the blank (SD_b):
- The blank measurement is typically the peak current obtained for a solution with no analyte present. It represents the background signal of your system.
- Assuming you have multiple blank measurements, calculate the standard deviation (SD_b) of these blank peak current values.
3. Calculate LoD and LoQ:
- LoD and LoQ are based on the standard deviation of the blank and the sensitivity (slope) of your calibration curve.
- LoD (Limit of Detection): This is the minimum concentration of analyte that can be distinguished from the background noise with a certain level of confidence (usually 95%). It is calculated as:LoD = 3 * SD_b / m
- LoQ (Limit of Quantification): This is the minimum concentration of analyte that can be quantified with a specific degree of accuracy (usually 10%). It is calculated as:LoQ = 10 * SD_b / m
Interpretation:
- A higher sensitivity (slope) indicates a larger change in peak current with increasing concentration, leading to lower LoD and LoQ values. This is desirable for better detection limits.
- Lower standard deviation of the blank (SD_b) also leads to lower LoD and LoQ values. This emphasizes the importance of minimizing background noise in your DPV measurements.