The Use of Disposable IR Cards for Quantitative Analysis Using an Internal Standard
Ramee Indralingam, Angelito I. Nepomuceno · Journal of Chemical Education · 2001
Infrared spectroscopy is traditionally used to identify compounds and aid in structure elucidation. However, solid samples require tedious and sometimes messy preparation of KBr pellets or mineral oil mulls and solutions cannot be used because there are no solvents that do not absorb in the IR. Disposable IR cards have simplified sample preparation for IR spectrometry. Moreover, they allow samples to be preserved for long periods, so that results can be verified at a later time. We report an experiment suitable for the instrumental analysis portion of the analytical chemistry course. It employs an internal standard in order to utilize the disposable cards for quantitative analysis. We use potassium thiocyanate as the internal standard because it has few absorption bands in the IR and they do not interfere with the bands of the unknown, benzophenone. Acetone is used as the solvent because it evaporates readily, making no contribution to the spectrum. This lab is useful as a teaching tool to illustrate the use of internal standards and calibration curves and the principle of Beer's law. It can be adapted for the determination of any analyte, provided the analyte and internal standard have distinctly separate IR bands. It is particularly useful in areas such as forensic chemistry, in which lab results are likely to be contested and samples must be preserved for long periods of time.