Flame Emission Spectroscopy (FES) is a powerful analytical technique widely used for identifying and quantifying elements in various samples. In this laboratory experiment, undergraduate students were introduced to FES and its significance in analytical chemistry. The experiment aimed to provide students with hands-on experience in constructing the FES instrument using low-cost readily accessible material and understanding its component's functions. The students prepared standard solutions of known concentrations of lithium (Li) to construct a calibration curve, using MATLAB program. They used a specially designed graphical user interface (GUI) for image-based data analysis to determine Li concentration in real samples using smartphone-captured flame images. To investigate the impact of interfering ions on Li analysis, students studied the effects of sodium (Na), potassium (K), and calcium (Ca) as interferents. The results showed that the designed FES instrument allowed accurate Li analysis in the presence of interfering ions with a relative error of less than 8%. The experiment provided students with valuable insights into error analysis, data interpretation, and the importance of accurate measurements in analytical chemistry. The practical training in assembling the FES instrument and using image-based data analysis tools enhanced students' practical skills and understanding of chemical analysis techniques.