Detector, atomic spectrometer diode array

During the last decade, research efforts in the field of LC-MS have changed considerably. Technological problems in interfacing appear to be solved, and a number of interfaces have been found suitable for the analysis of flavonoids. These include TSP, continuous-flow fast-atom bombardment (CF-FAB), ESI, and APCI. LC-MS is frequently used to determine the occurrence of previously identified compounds or to target the isolation of new compounds (Table 2.11). LC MS is rarely used for complete structural characterization, but it provides the molecular mass of the different constituents in a sample. Then, further structural characterization can be performed by LC-MS-MS and MS-MS analysis. In recent years, the combination of HPLC coupled simultaneously to a diode-array (UV-Vis) detector and to a mass spectrometer equipped with an ESI or APCI source has been the method of choice for the determination of flavonoid masses. Applications of LC-MS (and LC-MS-MS) in flavonoid... 

The tail of the plasma formed at the tip of the torch is the spectroscopic source, where the analyte atoms and their ions are thermally ionized and produce emission spectra. The spectra of various elements are detected either sequentially or simultaneously. The optical system of a sequential instrument consists of a single grating spectrometer with a scanning monochromator that provides the sequential detection of the emission spectra lines. Simultaneous optical systems use multichannel detectors and diode arrays that allow the monitoring of multiple emission lines. Sequential instruments have a greater wavelength selection, while simultaneous ones have a better sample throughput. The intensities of each element s characteristic spectral lines, which are proportional to the number of element s atoms, are recorded, and the concentrations are calculated with reference to a calibration standard. 

In the atomic emission detector (AI D), the effluent from the OC column is introduced into a microwavc-induced plasma (MIP), an inductively coupled plasma (ICP). or a direct current plasma (DCP). The MIP has l)cen most widely used and is available commercially. TTie MIP is used in conjunction with a diode array or chargc coupled-device atomic emission spectrometer as shown in I igure27-I2. The plasma is sufficiently en-... 

The AED employs a microwave-induced He plasma to dissociate eluted analyte molecules to their component atoms and excite them to emit at characteristic wavelengths. This is very similar to the mechanism in the argon plasma inductively coupled plasma source (cf. Section 7.3.1). A spectrometer with a diode array detector (Figure 7.26b and c) isolates and measures the intensity of sensitive emission lines unique to each element. Depending on the relative sensitivity and proportion of atoms in the molecules, separate element response channels may display peaks in several element-selective chromatograms. These data may be combined with retention... 

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