1. History

Historically, the eye was the first detector used (spectroscopy). Its sensitivity is limited by definition to the visible range (400-700 nm), and while the eye can compare intensities, it cannot accurately assess an absolute intensity. Nevertheless, the eye is a sensitive detector, particularly of yellow light, and in the 19th century it was possible to detect a few mg/L of Na in a flame. Analytical atomic spectrometry, in this case emission spectrometry, only became quantitative with the use of the photographic plate (spectrography). The photographic plate has many advantages, not least the amount of information that can be stored on it. It's easy to record several complete spectra over a wide range of wavelengths. On the other hand, the plate requires development to reveal the information, its measurement dynamic range is very low, and its use for quantitative analysis requires the use...