Scattered light...the curse of modern spectrofluorometry And how SLM/AMINCO instruments have solved the problem. The most serious problem caused by scatter interference is that it limits the minimum detectable quantity of a compound more than any other factor, excepting only the compound's fluor escence efficiency (see Fig. 1).
signal to noise ratio for a holographic grating will be, at the worst, six-to-seven fold better than for the classicallyruled grating (at the latter's maximum).
A slice right out of the melon T h e good news is that the curse of scattered light can be —and has been — solved. How effectively? A good example was afforded to us at a recent West Coast exhibit. Upon arriving, we were dismayed to discover that we had brought no sample to scan on a working instrument. Even worse, we had shipped no cuvettes. So, inspired by desperation, we bought a melon, sliced off a chunk of rind, inserted it in the sample compartment and scanned. T h e resulting spectra were essentially free of scatter-induced artifact, despite these artificially demanding circumstances. efficiency everywhere but near the blaze wavelength (see Fig. 2). Our experience is that stray light from a finely-ruled (1200 lines/mm) holographic grating is about an order
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Fig. 1 Sample fluorescence is a minor constituent of this combined scatter/fluorescence peak at full scale deflection.
T h e three secrets: optics, optics, optics The monochromator grating is the key to minimizing scattered light. Gratings are of two types: classicallyruled and holographic. T h e peak efficiency of the holographic grating is generally lower, but the curve is flatter, which translates to a higher
Fig. 2. The efficiency curve of a holographic grating is generally lower but flatter than that of a ruled grating if 0.2
