Chromatogram analysis
If you count from the baseline, you can see that the curve contains a defined area under it. The peak area is used to make the calibration. This is done because that area is proportional to the concentration of the analyte. The higher the concentration, the larger the peak and, thus, the higher the peak area.
Once you have plotted the points using the peak areas of the known concentrations, you can make linear regression analysis (y = mx + y0) to find out the equation that relates the peak area and the concentration of the analyte. The peak area is plotted on the y axis and the analyte concentration is plotted on the x axis. y0 is the point where the line intersects the y axis, which is constant. When you apply a linear regression analysis, you will be able to determine the slope (m) of the line. Thus, you can use the peak area that was processed for your unknown sample and calculate the concentration of the analyte, as shown in the Figure 1.
Figure 1. Calibration curve showing the relation between peak area to the concentration.