Instrumental bandwidth reducing

Altogether, the results deliver a clear answer to the question, what is the optimal instrumental bandwidth for CS AAS. The bandwidth should never be chosen smaller than two times the FWHM of absorbing lines. Higher values for AAinstr will not significantly reduce the shot-noise limited Amin- Nevertheless they should be avoided to allow the best possible background correction (BC). With respect to the results presented in Section 2.1.5, an optimized value for the instrumental resolving power / = A / AA is between 50 000 and 150000. 

Filters obviously do not provide monochromatic radiation and in many cases the bandwidth may be as great as 100-150 nm (Figure 2.19). Increasing the concentration of the dye may reduce the bandwidth to some extent but will also reduce the amount of radiation transmitted and this then will impose a strain on the detecting system and the sensitivity of the instrument. 

The procedures described next were developed for the deconvolution of electronic absorption spectra (UV-visible spectra) but are equally applicable to the deconvolution of infrared, Raman or NMR spectra. UV-visible spectra differ from vibrational spectra in that the number of bands is much smaller and the bandwidths are much wider. Band shape may also be different. UV-visible spectra are also usually recorded under conditions of high resolution and high signal-to-noise ratio. Spectra from older instruments usually require manual digitization from a spectrum on chart paper, at e.g., 10 nm intervals. With the widespread use of computer-controlled instruments, it is a simple matter to obtain a file of spectral data at, e.g., 1 nm intervals. In fact, it may be necessary to reduce the size of the data set to speed up calculations. 

Turbidity meters with narrow-band near infrared (NIR) light sources (peak output at 0.86 pm spectral bandwidth <0.06 pm) are recommended by ISO. Such instruments reduce problems of algal build-up on the optical surfaces, are less affected by color, and are more sensitive to the slightly larger particles typical of sediment transport systems. However, some relaxation of the infrared protocol is tolerable for field instruments operating in continuous monitoring mode. 

---