5. Measurement Modes
The design of an analytical instrument based on spectroscopy depends on the nature of the energetic transitions involved (e.g., electronic, vibration, rotation, translation, nuclear), the nature of the radiative process involved (e.g., absorption, emission, fluorescence) and the nature of the food matrix (e.g., absorbing or non-absorbing).� These factors determine the wavelength (frequency) of electromagnetic radiation used, the way that the electromagnetic radiation is generated and the way that the electromagnetic radiation is detected.� Some commonly used designs are highlighted below:
� Emission.� The sample being analyzed is energetically stimulated (e.g., by heating or application of radiation) and the amount of electromagnetic radiation produced by the sample is measured at different wavelengths, e.g., atomic emission spectroscopy, NMR, fluorescence.
� Transmission. An electromagnetic wave generated by the analytical instrument is propagated directly through the sample and the reduction in its amplitude due to interaction with the sample is measured at different wavelengths, e.g., atomic absorption spectroscopy, infrared transmission measurements, UV-visible spectrophotometery.
� Reflection. An electromagnetic wave generated by the analytical instrument is reflected from the surface of the sample and the reduction in its amplitude due to interaction with the sample is measured at different wavelengths, e.g., infrared reflection measurements, color measurements.