The ability of students to perform quantitative analysis is a fundamental aspect of analytical chemistry courses and laboratories. In this laboratory experiment, students quantitatively analyze both liquid and solid samples through the use of internal standard calibration and ATR-FTIR spectroscopy. Using a problem-based approach to selecting their internal standards, students gain a deeper understanding of the internal standard method of calibration and the process of selecting appropriate standards for the analysis of sodium benzoate and acetophenone. This experiment allows students to explore the internal standard method of calibration under a wider context of quality control and quality assurance as they frame their quantitative analyses through both internal and external quality assurance testing methods. In a survey of students undertaking this experiment, most students responded that the experiment provided them with a better understanding of the internal standard method of calibration, and the selection of internal standards, and offered them an opportunity to gain hands-on experience with ATR-FTIR spectroscopy.