Diode-array technology

With the introduction of diode-array technology in the 1980s, a further dimension is now possible because coupled LC-UV with diode array detection (DAD) allows the chromatographic eluent to be scanned for UV-visible spectral data, which are stored and can later be compared with a library for peak identification. This increases the power of HPLC analysis... 

Introduction to all forms of spectroscopy including UV-VIS, NMR, and MS http //www scimedia com/chem-ed/spec/uv-vis/uv-vis htm Theory and practice of spectroscopy http //chemistry gsu edu/post docs/koen/wuvhtml Read Theory and Spectra Interpretation http //chem external hp com/cag/products/uvistech html Introduction and applications of diode array technology http //www cis rit edu/htbooks/nmr/... 

The introduction of rapid-scanning UV-VIS detectors based on diode-array technology has been of great assistance in confirming the identity of peptides that contain aromatic residues (Phe, Tyr, and Trp). The advantage of these detectors lies in their ability to store spectra for subsequent use. 

Concerning the portable instrument (PASTEL UV), a Diode Array technology has been developed and the optical system is designed as shown on Figure 2.4.2. 

The general optical design is the same as described for the PASTEL UV (Diode Array technology, Deuterium lamp for high measuring dynamic and reproducible results). 

Most applications depend on the understanding of the limitations of the detection principles and of the equipment used, which helps to avoid trivial errors. For this reason, after a short introduction to the theoretical fundamentals, different types of instrumentation are compared with respect to sample handling and error avoidance. Besides absorption, the suitability of fluorescence, reflectance, and interferometry are demonstrated. Some new applications by use of fiber optics and diode array technology are given. Measurements in turbid solution are introduced and a few clinical examples are mentioned. Finally, principles of multicomponent analysis are discussed. 

Diode array technology is another leading candidate for measuring color, as well as other visible properties, of specimens. Polychromatic hght reflected or transmitted from a specimen is dispersed by a grating and focused on an array of detectors, each detecting a specific wavelength interval (38) (Fig. 3). Instrument examples of this are Zeiss OFT 311, OFR 311, and MCS 2 x 511 (Fig. 4). 

Procedure Phenolic acids were detected between 210 and 360 nm using a Hewlett Packard diode array detector (HP 1100 HPLC system). The separation was achieved with a Nucleosil 100-5 C18 column 5 pm 4.0x250 mm (Agilent Technologies, USA) at a flow rate of 1.0 ml/min and injection volume of 5 mL. For the elution, a discontinuous acetonitrile-water gradient was used 15% acetonitrile (5 min), 30% acetonitrile (20 min), 40% acetonitrile (25 min), 60% acetonitrile (30 min), 60% acetonitrile (35 min) and... 

For reference methods, HPLC with various detectors has become the standard reference technique for analysis of food additives, but new developments in this area are mainly linked to detector technology. Diode array detectors have not totally met the expectations of food analysts in terms of their specificity and LC-MS is likely to fill the gap. Specific detection with biosensor chips may also have a future for certain analyses. The use of combined LC-MS/DAD systems is... 

Agilent Technologies Agilent CE General purpose Diode array detection... 

Near-infrared Spectroscopy for Process Analytical Technology 119 5.3.2 The scanning grating monochromator and polychromator diode-array... 

Attenpts to Analyze Complex Polymers Using SEC Detector Technology. For linear copolymers, multiple detectors and, more recently, diode array UV/vis spectrophotometers have been used in attempts to overccxne the above analysis problems. The basic idea is to provide more than one detector response so that the polymer concentration and the number of properties will together equal the number of detector responses (Figure 4). This provides the same number of equations as the number of unitnowns (5,6). 

Detector Technology. For copolymer composition analysis the new diode array UV/vis detectors are extremely attractive the absorption at many wavelengths are instantaneously recorded there is only a single spectrophotometer cell so that transport time delays between detectors and axial mixing in detector cells do not confound comparison of detector response at different wavelengths and for styrene copolymers, extremely low concentrations of polymer can be detected. 

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... 

These three examples illustrate technology developments over time (dual-channel detector, diode array detector, mass spectrometer). Note that while the overall methodology is very similar (methanolic extracts, methanol-based, acidified solvents used for HPLC, detection of eluted compounds), the exact conditions for successful separation need to be defined for each system. 

Huber, L. Applications of Diode-Array Detection in HPLC. Waldbronn, Germany Agilent Technologies (1989), publ. number 12-5953-2330. 

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