Diode array detector wavelength

Separation of C oand C70 can be achieved by HPLC on a dinitroanilinopropyl (DNAP) silica (5pm pore size, 3(X)A pore diameter) column with a gradient from H-hexane to 50% CH2CI2 using a diode array detector at wavelengths 330nm (for C q) and 384nm (for C70). [J Am Chem Soc 113, 2940, 1991.]... 

Such effects principally cannot be observed in multi band detectors such as a UV diode array detector or a Fourier transform infrared (FTIR) detector because all wavelengths are measured under the same geometry. For all other types of detectors, in principle, it is not possible to totally remove these effects of the laminar flow. Experiments and theoretical calculations show (8) that these disturbances can only be diminished by lowering the concentration gradient per volume unit in the effluent, which means that larger column diameters are essential for multiple detection or that narrow-bore columns are unsuitable for detector combinations. Disregarding these limitations can lead to serious misinterpretations of GPC results of multiple detector measurements. Such effects are a justification for thick columns of 8-10 mm diameter. 

This an excellent example of the value of the diode array detector. If the chromatogram shown in figure 3 was monitored at two different wavelengths, then a peak ratio curve would immediately disclose the presence of the second peak (see page 175) and it would no longer be necessary to resort to changes in mobile phase composition to establish the presence of the impurity. 

It is seen that however sophisticated the software might be, it would be virtually impossible to de-convolute the peak into the three components. The peaks shown in the diagram are discernible because the peaks themselves were assumed and the composite envelope calculated. The envelope, however, would provide no basic data there is no hint of an approximate position for any peak maximum and absolutely no indication of the peak width of any of the components. The use of the diode array detector, monitoring at different wavelengths, might help by identifying uniquely one or more of the... 

THF = tetrahydrofuran. ACN = acetonitrile, p.s. = particle size. i.d. = internal diameter, o.d. = outer diameter. MeOH = methanol. MS = mass spectrometry. DAD = diode array detector, n.a. = not available. THC = tetrahydrocurcumin. = exdtation wavelength. X = emission wavelength. 

Investigations relying on HPLC coupled to a UV-Vis detector should be set at 470 to 475 nm for betaxanthins and 535 to 540 nm for betacyanins. Gradient elution is commonly preferred to achieve complete separation. If a diode array detector is available, common monitoring wavelengths are 280 nm for colorless phenolics, 406 nm for betalamic acid, 470 nm for betaxanthins, and 536 nm for betacyanins. 

Some analytical instruments produce a table of raw data which need to be processed into the analytical result. Hyphenated measurement devices, such as HPLC linked to a diode array detector (DAD), form an important class of such instruments. In the particular case of HPLC-DAD, data tables are obtained consisting of spectra measured at several elution times. The rows represent the spectra and the columns are chromatograms detected at a particular wavelength. Consequently, rows and columns of the data table have a physical meaning. Because the data table X can be considered to be a product of a matrix C containing the concentration profiles and a matrix S containing the pure (but often unknown) spectra, we call such a table bilinear. The order of the rows in this data table corresponds to the order of the elution of the compounds from the analytical column. Each row corresponds to a particular elution time. Such bilinear data tables are therefore called ordered data tables. Trilinear data tables are obtained from LC-detectors which produce a matrix of data at any instance during the... 

Polar or thermally labile compounds - many of the more modern pesticides fall into one or other of these categories - are not amenable to GC and therefore LC becomes the separation technique of choice. HPLC columns may be linked to a diode-array detector (DAD) or fluorescence detector if the target analyte(s) contain chromophores or fluorophores. When using a DAD, identification of the analyte(s) is based on the relative retention time and absorption wavelengths. Similarly, with fluorescence detection, retention time and emission and absorption wavelengths are used for identification purposes. Both can be subject to interference caused by co-extractives present in the sample extract(s) and therefore unequivocal confirmation of identity is seldom possible. 

Series 10 chromatography LC-95 variable wavelength UV/visible detector, LC-90 variable wavelength UV detector, LC-135 and L-235 diode array detectors, LC 1-100 computing integrator, 1SS-100 intelligent amjj in s stjm, Series 410 LC pump... 

A diode array detector is well suited to achieve these goals. Full range spectra should be collected for the method development samples and evaluated with two-dimensional or three-dimensional visualization to determine the best detection wavelength. 

The wavelength accuracy of the diode array detector is commonly determined by comparing a measured absorbance with the absorbance maxima of a reference... 

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