Detectors ultraviolet detection

ECD = electron capture detector FID = flame ionization detection GC = gas chromatography HECD = Hall electrolytic conductivity detector HRGC = high-resolution gas chromatography HSD = halogen-specific detector H2SO4 = sulfuric acid MS = mass spectrometry NR = not reported PID = photoionization detection UV = ultraviolet detection... 

Detection in 2DLC is the same as encountered in one-dimensional HPLC. A variety of detectors are presented in Table 5.2. The choice of detector is dependent on the molecule being detected, the problem being solved, and the separation mode used for the second dimension. If MS detection is utilized, then volatile buffers are typically used in the second-dimension separation. Ultraviolet detection is used for peptides, proteins, and any molecules that contain an appropriate chromophore. Evaporative light scattering detection has become popular for the analysis of polymers and surfactants that do not contain UV chromophores. Refractive index (RI) detection is generally used with size exclusion chromatography for the analysis of polymers. 

In liquid chromatographic analysis of macrolides and lincosamides, most popular is the ultraviolet detector (Table 29.4). Tylosin, tilmicosin, spiramycin, sedecamycin, and josamycin exhibit relatively strong ultraviolet absorption, but erythromycin, lincomycin, pirlimycin, and oleandomycin show extremely weak absorption in the ultraviolet region. Hence, detection at 200-210 nm has been reported for the determination of lincomycin (146). However, a combination of poor sensitivity and interference from coextractives necessitated extensive cleanup and concentration of the extract. Precolumn derivatization of pirlimycin with 9-fluorenylmethyl chloroformate has also been described to impart a chromophore for ultraviolet detection at 264 nm (140). 

Water is so transparent that ultraviolet detectors can operate at wavelengths as short as 185 nm. where most solutes have strong absorption. To take advantage of short-wavelength ultraviolet detection, background electrolyte must have very low absorption. Borate buffers are com-... 

Direct determination of urea pesticides by high-performance liquid chromatography has been widely reported in the literature (10,32-36,127-130). Ultraviolet detection has often been used (32,33,35,36,60,127) with usually acceptable sensitivity, although this detector is nonspecific and the sensibility is, in general, low. To overcome this problem, several techniques have been assayed, such as precolumn enrichment (60), postcolumn derivatization (34,10), and the use of other detection techniques such as the electrochemical (129), photoconductivity (128,130), and fluorescence detectors (9,10,34). Table 9 summarizes representative papers using these techniques in HPLC analysis. 

While HPLC does not always produce superior results to those with TLC it allows greater versatility and is more suitable for the analysis of complex organic matrices such as cereals. HPLC coupled to sensitive detection and sophisticated data retrieval has improved the identification of selected mycotoxins at levels much less than achieved by TLC. Additional chromatographic modes such as normal-phase, reverse phase and ion-exchange chromatography have been employed. There are no truly universal detectors available for HPLC. Detectors presently in use include Fourier transform infrared detections (FT-IRD), diode array ultraviolet detection (DAD) and mass selection detectors (MSD) (Coker, 1997). 

Specialized Stationary Phases for Liquid Chromatography Chiral Stationary Phases for Liquid Chromatography Detectors for Liquid Chromatography Ultraviolet Detection of Chromophoric Groups Derivatizing Reagents for HPLC... 

An ultraviolet detector used in series with a conductivity detector is the basis for a method [39] for the determination of anions in non saline waters. This combination of detectors greatly increases the amount of information that can be collected on a given sample. The application of ultraviolet detection has the following advantages ... 

In areas where the possibility of fire is the greatest, a high speed ultraviolet detection system is employed. The ultraviolet eyes detect the presence of a flame and are interconnected with a high speed water deluge system. In some areas the fire detection devices have process shutdown capabilities. The detectors are situated such that the entire hazardous area can be monitored at all times. They are equipped with air shields that not only cool the detector but also blow clean air across the face of the lens, keeping any dust from accumulating on the lens, which assures detection capability. Further, the detectors have a built-in test lamp which serves as a check of... 

Ultraviolet, fluorometric, and mass spectrometric detectors have aU been successfully used for the determination of residues of quinolones in food. Quinolones exhibit remarkable ultraviolet absorption therefore, they are ideal for direct determination by ultraviolet detection anywhere in the wavelength range from 254 to 295 nm. However, the most popular is fluorometric detection, due to the... 

Until recently the main disadvantage of this technique was the poor sensitivity of the detectors. Development of more sensitive detectors such as a reductive amperometric electrochemical detection, ultraviolet detection, ICP-AES, ICPMS, AFS, and AAS has resulted in wider applications in environmental studies. The main advantage of liquid chromatography is the possibility to separate a great variability of organomercury compounds. Applications of HPLC for Hg speciation studies have been reviewed by Harrington. ... 

EDCs in the environment are often analyzed using GC or LC based instrumental techniques. GC coupled with an electron capture detector (BCD), a nitrogen-phosphorus detector (NPD), or mass spectrometry (MS) has been the preferred method due to its excellent sensitivity and separation capability on a capillary column. High performance liquid chromatography (HPLC) with various detectors such as ultraviolet detection (UV), fluorescence detection (FLD), MS, and more recently tandem MS (MS/MS) has also been used for analysis of some EDCs, especially for the polar compounds. Analytical techniques for each class of EDCs will be discussed in the following section. 

Peak height ratios for different detectors or, e.g., ultraviolet detection at several wavelengths, can be used. Another method is to observe the change in retention times upon derivatization of the sample either by chemical or enzymatic methods. With continuous wavelength detectors stopped flow scanning of ultraviolet or fluorescence spectra is a possibility. Isotopic labelling can be used and, finally, fractions can be collected and characterized by, e.g., spectroscopic methods. 

Ultraviolet detection is at 210 nm or, additionally for Emoc derivatives, 266 nm. Note that such detection will not show free amino acids and, unless these have aromatic side chains or UV-absorbing side-chain protecting groups, it will be necessary to use a conductivity detector. 

The eluants employed for HPLC separations may comprise water, aqueous buffer solutions, miscible organic solvents such as methanol and acetonitrile or a mixture of the above. All solvents should be of high spectroscopic purity, dust-free, and should be filtered and degassed (i.e. have dissolved gases displaced) before use. They should also, if ultraviolet detection is being employed, be transparent to the detector wavelength employed. 

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