Beer's law scatter plot and trend line (linear regression) Eng. Haneen Nabil AL-Sbaihi Environmental Engineering Department Islamic University of Gaza In mathematical equations you will encounter in this course, there will be a dependent variable and an independent variable. Identifying the dependent and independent variables in a mathematical equation will help you identify what you are solving for in the equation. The independent variable is a variable whose value determines the value of the dependent variables. Independent variable is plotted on the Xaxis, and the dependent variable is plotted on the Y-axis. Other variables may also be present in equations. These may be constants or other variables. They may be given to you or you may be required to obtain them by performing curve fitting. The example below illustrates this point. Equation 1: y = mx + C y = dependent variable x = independent variable m and C = constants A calibration curve or standard curve is usually using series of standard solutions known concentrations is prepared and measured using spectrophometer instrument to determine the unknown concentration of sample. It is represent a graph where concentration is plotted against absorbance then a straight line (Beer's Law) is fit to the data that you obtained and the resulting equation is used to convert absorbance of the unknown sample into concentration. To plot any data in excel, you should enter the data, create a scatter plot with only Markers from data, and then add linear regression (trendline) to make