Determination of Unknown Concentrations of Sodium Acetate Using the Method of Standard Addition and Proton NMR: An Experiment for the Undergraduate Analytical Chemistry Laboratory

In this experiment, students learn how to find the unknown concentration of sodium acetate using both the graphical treatment of standard addition and the standard addition equation. In the graphical treatment of standard addition, the peak area of the methyl peak in each of the sodium acetate standard solutions is found by integration using proton NMR. Using the calibration curve of the peak areas of the methyl protons of sodium acetate versus the concentration of the sodium acetate solutions, the concentration of the unknown is determined through extrapolation to the x axis. In a separate experiment, the unknown concentration of sodium acetate is found using the standard addition equation. In this case, the methyl peak areas in the unknown sodium acetate solution and the unknown sodium acetate spiked with a standard are obtained using proton NMR. The standard addition equation is then used to find the concentration of the unknown. This experiment has been successfully used in the undergraduate analytical lab and students have learned the method of standard addition to find unknown concentrations of sodium acetate in the millimolar range. It has also given them the opportunity to have hands-on experience using NMR spectroscopy as a quantitative tool.