Spectral bandwith

Absorption and CD spectra should be acquired with instruments that are capable of achieving spectral bandwidths of 1 nm or less over an ultraviolet wavelength range of 190 to 350 nm. Sample temperatures must be controlled. Spectra shown in this chapter have been obtained at 20° 5° with a Cary Model 118 spectrophotometer and a Jasco Model J500A spectropolarimeter. Typically, the spectrophotometer is operated with a scan speed of 0.5 nm/sec and a period of 1 sec, in the auto slit mode with the gain set so that the spectral bandwidth is always less than 1 nm. The spectropolarimeter is set to a time constant of 1 sec, a scan speed for single scans of 10 nm/min, and a spectral bandwith of 1 nm. 

Only in the case of some alkali metals which have some few widely spaced resonance lines across the visible spectrum, may this be achieved by simple filter monochromators. For the determination of most elements, however, high quality UV/VIS monochromators are required that are capable of achieving a spectral bandwith of the order of 0.1 nm. Such monochromators are nowadays implemented in most commercial AA instruments. The optical components used (particularly, monochromators and detectors) are very similar to those used for emission spectroscopy and will be discussed in more detail later. 

An important parameter of a spectrometer is the relative bandwith RB. It is defined by the spectral bandwidth of the spectrometer relative to the linewidth to be recorded. 

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