How can the presence of impurities be determined using IR spectroscopy?

The presence of impurities in a sample can be effectively determined using infrared (IR) spectroscopy by identifying the bond types within the molecule. Each functional group within a compound has a characteristic absorption pattern in the IR spectrum, which corresponds to the vibrations of bonds between atoms. When a sample contains impurities, additional peaks or shifts in the expected absorption bands may be observed.

For instance, if a pure compound typically shows absorptions at certain wavelengths due to its characteristic functional groups, the introduction of an impurity may result in additional peaks indicating the presence of different functional groups or alterations in the molecular environment. By analyzing these changes, one can infer the presence of impurities, making IR spectroscopy a valuable tool in determining sample purity.

The other options do not directly relate to the capability of IR spectroscopy to identify impurities. Molecular mass is measured using techniques like mass spectrometry, while melting point analysis typically provides information about sample purity but does not identify the types of bonds present. Similarly, the refractive index is a property that can indicate changes in purity but does not provide specific information about the functional groups or bonds in the sample.