Why are hollow cathode lamps used for atomic absorption spectroscopy?
Atomic absorption lines are very narrow.
For the Beer-Lambert law to be applicable, the bandwidth of the source should be narrow in comparison with the width of the absorption peak. Otherwise, the signal-to-noise ratio and the slope of the calibration curve would be low; the resulting sensitivity would be poor.
Continuous radiation sources use monochromators; however, even good monochromators have effective bandwidths that are significantly greater than the width of atomic absorption lines.
Therefore, the use of line sources with bandwidths even narrower than the width of absorption peaks is preferred.