ABSTRACT
A detector is necessary to measure either radiation produced by the sample in emission or fluorescence or the radiation transmitted through the sample in absorbance spectroscopic methods. In absorption spectroscopy, a sample is irradiated with electromagnetic radiation, and the amount which passes through is monitored. Atomic absorption and emission spectroscopy in the ultraviolet and visible regions are used to determine metals in samples derived from air, water, or solids. The radiation is detected and its frequency and intensity give information about the identity as well as the amount of the radiating species. In absorption, radiation is passed through the sample. The absorption of incident radiation is governed by Beer's law. Sample molecules may be excited by absorbed radiation. These may undergo a radiationless transfer to a lower energy state, before emitting the remaining excess energy as radiation and dropping back to the ground state. Atomic emission spectroscopy uses the radiation emitted from excited atoms in a vapor state.
