A Rotating Filter Disc Alternative to Photodiode Array Detection Systems
With traditional single-wavelength monitoring, solute discrimination depends totally on retention-time data. With two detectors coupled in series, absorbance ratios are also obtainable; thereby compounds for which the UV profiles appear very similar have been successfully distinguished. Since, however, reproducibility problems can arise with dual detector systems, we developed our own multi-wavelength detector. At the outset, photodiode arrays were not available commercially, and a detector based upon a rotating filter disc was conceived. The disc can hold up to 4 interference filters (UV or visible), and is rotated at a constant speed (2 rev/sec). The absorbance data from the 4 wavelengths are stored on a computer and then processed very quickly, with no operator involvement, to produce a summary of absovbances, absorbance ratios and retention-time data at the end of a chromatographic run.
Consideration is given below to the design of the detector for operation in the UV or visible mode, to performance and cost, and to applications of absorbance ratioing for discriminative purposes as exemplified by the analysis of drugs including barbiturates and dyes. The design is compared with that of multi-wavelength detectors based on photodiode arrays.
KeywordsRelative Retention Time Absorbance Ratio Methyl Violet Filter Disc Visible Mode
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