Detector wavelength robustness

Robustness Systematically change chromatographic conditions (examples column temperature, flow rate, gradient composition, pH of mobile phase, detector wavelength). Check influence of parameters on separation and/or peak areas. 

The robustness of a method is a measure of the method s ability to remain unaffected by small but deliberate changes to the method parameters (e.g., flow rate, detector wavelength, etc. see Table 8.6 for some further examples). 

Another goal of validation is to show that a method is robust, which means that it is not affected by small changes in conditions. For example, a robust chromatographic procedure gives reliable results despite small changes in solvent composition, pH, buffer concentration, temperature, injection volume, and detector wavelength. 

Detection Most pharmaceutical compounds have UV chromophores. UV detector is the most commonly used detector. Wavelengths at Xmax or X ai are usually selected for method robustness. For example, three wavelengths at 265 (Xmax), 226 (Xvai), and 210 nm (Xmax) can be potentially used for a compound with the UV profile shown in Figure 1.2. However, sensitivity is the highest at 265 nm, which is why 265 nm should be selected for best detection. In addition, UV profiles of impurities in the sample should be considered. A detection wavelength should be selected to ensure that all components have acceptable sensitivity, not just the major component. 

Rl detector Robustness variable wavelength UV detector, ELSD, electrochemical detector,... 

The imaging detectors, whether for point mapping, line scanning, or array detection, can be coupled with different types of spectrometers. Instrument types are classified by wavelength selection modality into imaging Fourier transform (FT) and tunable filter (TF) spectrometers, both of which are presented below, and dispersive spectrometers. FT imaging systems are classical laboratory instruments while TF spectrometers are compact and robust systems for chemical imaging. 

If the components to be detected fluoresce, a fluorescence detector can be employed. A mercury or xenon lamp with a monochromator is used as the source for the exitation wavelength. Modern systems use lasers as light source, but such systems are mainly used in trace analysis and not in preparative systems. The main advantage of fluorescent detectors is their high sensitivity. Their reduced robustness and limitation to fluorescent compounds makes them not widely used in preparative chromatography. 

The application of NIR luminescent materials depends on the availabiUty of robust, cost-effective excitation sources and light detectors for such materials. For NIR luminescent lanthanide complexes, it is especially the relatively limited choice of accessible detectors that has slowed their investigation and further development. Most standard spectrofluorimetric and microscopic equipment are equipped with detectors that are mainly sensible in the visible. An extension of the spectroscopic sensitivity of this equipment farther into the red usually does not go to wavelengths longer than 850 nm (the limit of typical multi-alkali photocathodes). We will briefly discuss some recent developments in excitation sources and detectors that are applicable in particular to NIR luminescent lanthanide complexes. 

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