Diode array detector time resolution

Because polyphenolics show chemical complexities and similar structures, isolation and quantification of the individual polyphenolic compounds have been challenging. Many traditional techniques (paper chromatography, thin-layer chromatography, column chromatography) have been used. HPLC, with its merits of exacting resolution, ease of use, and short analysis time, has the further advantage that separation and quantification occur simultaneously. A reversed-phase HPLC apparatus equipped with a diode array detector makes possible the easy isolation and separation of many polyphenolics. For enhanced performance of HPLC separation, the polyphenolics should first be isolated into several fractions to effectively separate the individual polyphenolics (Jaworski and Lee, 1987 Oszmianski and Lee, 1990). 

UV diode array and fast scanning detectors not only enable the generation and use of libranes of known natural product standards, but can also enhance chromatographic resolution. This enhancement is due to peak punty assessment, which allows the researcher automatically to compare UV spectra at different time points across a peak of interest and thus detect the presence or absence of multiple poorly resolved components. This feature is generally included in the standard software of most commercially available diode array detectors. 

For detection in the UV-visible region, photomultipliers or other photoelectric devices are used. Some instruments may use a multi-channel diode array detector. An array of typically 300 silicon photodiodes detects all the wavelengths simultaneously with a resolution of about 1 nm. This provides a great saving in time and an improved signal/noise ratio. 

If the retention times of the compounds to be separated are known, or if they can be detected by using UV (including diode arrays), radiochemical or fluorescence detectors, stop-flow LC-NMR becomes an option. Upon detection, the PC controlling the liquid chromatograph allows the pumps to continue running, moving the peak of interest into the NMR probe. Once the pumps have stopped, normal high-resolution NMR spectroscopy is possible. It could be... 

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