Ultraviolet HPLC detector

Liquid chromatography with TEA detection or an ultraviolet HPLC detector has been evaluated as an analytical procedure that simultaneously determines EGDN and NG in air [57], Samples were collected by drawing a known volume of air through large sampling tubes containing Tenax-GC resin. The samples were desorbed with methyl alcohol and analysed by LC with TEA or an UV HPLC detector. A Dupont Zorbax CN... 

The results from conventional gel permeation chromatography (GPC) of four acetylated aspen lignin derivatives are shown in Table 1. These data were collected with a sensitive ultraviolet HPLC detector, permitting 0.2 mg column loadings. The values for, and (35) proved to be similar to those... 

Hplc techniques are used to routinely separate and quantify less volatile compounds. The hplc columns used to affect this separation are selected based on the constituents of interest. They are typically reverse phase or anion exchange in nature. The constituents routinely assayed in this type of analysis are those high in molecular weight or low in volatility. Specific compounds of interest include wood sugars, vanillin, and tannin complexes. The most common types of hplc detectors employed in the analysis of distilled spirits are the refractive index detector and the ultraviolet detector. Additionally, the recent introduction of the photodiode array detector is making a significant impact in the analysis of distilled spirits. 

HPLC) system equipped with an ODS column and ultraviolet (UV) detector for quantitative determination. 

The most basic method for the determination of the methylxanthines is ultraviolet (UV) spectroscopy. In fact, many of the HPLC detectors that will be mentioned use spectroscopic methods of detection. The sample must be totally dissolved and particle-free prior to final analysis. Samples containing more than one component can necessitate the use of extensive clean-up procedures, ajudicious choice of wavelength, the use of derivative spectroscopy, or some other mathematical manipulation to arrive at a final analytical measurement. A recent book by Wilson has a chapter on the analysis of foods using UV spectroscopy and can be used as a suitable reference for those interested in learning more about this topic.1... 

HPLC has been used, with an ultraviolet absorption detector set for 254 nm, for the determination of aromatic hydrocarbons and with a flow calorimeter for the detection of all hydrocarbons. Increased sensitivity and decreased interference can be achieved with the ultraviolet absorption detector by measuring absorption at two wavelengths and using the ratios of the absorption at those wavelengths [28]. 

The ultraviolet (UV) absorption HPLC detector is basically a UV spectrophotometer that measures a flowing solution rather than a static solution. It has a light source, a wavelength selector, and a phototube like an ordinary spectrophotometer. The cuvette is a flow cell, through which the column effluent flows. As the mobile phase elutes, the chromatogram traces a line at zero absorbance, but when a mixture... 

From the available analytical techniques, the most commonly employed is HPLC coupled with an ultraviolet (UV) detector, which provides a rapid, relatively cheap and easy routine analysis of conjugated BAs from serum samples. HPLC with UV detection determination does not require sample derivatisation, but the sensitivity of... 

An ultraviolet detector using a flow cell such as that. in Figure 25-19 is the most common HPLC detector, because many solutes absorb ultraviolet light. Simple systems employ the intense 254-nm emission of a mercury lamp. More versatile instruments have deuterium, xenon, or tungsten lamps and a monochromator, so you can choose the optimum ultraviolet... 

Fig. 45 Reversed-phase HPLC of autoxidized trilinolenin (peroxide value = 236.4 meq/kg). Nova-Pak C18 cartridge column (Waters, Milford, MA) (3.9 X 150 mm, 60 A, 4 yam), mobile phase acetonitrile/ dichloromethane/methanol (80 10 10). Ultraviolet (UV) detector (235 nm) and evaporative light-scattering detector (ELSD). Primary oxidation products, double peak at 3.6 min secondary oxidation products elute before primary oxidation products.

Baker and Bottomly [80] developed a multi-residue method for the determination of synthetic pyrethroids in fruit and vegetables. After extraction with hexane-acetone, the pyrethroids are separated from coextractives by a partition process and chromatography on a silica gel column and quantitatively determined by electron-capture gas-liquid chromatography and/or HPLC using an ultraviolet spectrophotometric detector. 

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). 

To be effective, the detector must be capable of responding to concentration changes in all of the compounds of interest, with sensitivity sufficient to measure the component present in the smallest concentration. There are a variety of HPLC detectors. Not all detectors will see every component separated by the column. The most commonly used detector is the variable ultraviolet (UV) absorption detector, which seems to have the best combination of compound detectability and sensitivity. Generally, the more sensitive the detector, the more specific it is and the more compounds it will miss. Detectors can be used in series to gain more information while maintaining sensitivity for detection of minor components. 

Verhaar et al.18 described the HPLC analysis of reaction mixtures of lactose (oxidation and degradation). In this work, a refractive index (RI) detector coupled with a variable wavelength ultraviolet (UV) detector at 212 nm was used to monitor the... 

A typical pSFC instrument, at first glance, is designed like an HPLC system. The major differences are encountered at the pump, the column oven, and downstream of the column. pSFC is best carried out using pumps in a flow-control mode. A regulator mounted downstream of the column and ultraviolet-visible detector (UV) controls the pressure drop in the chro-... 

As far as the conversion of the analytical response is concerned, the most used detectors in GrFFF have been, until now, conventional ultraviolet (UV) detectors commonly used for HPLC. With this type of detector, the amount of particles with diameter di is proportional to the detector response at the zth point. With particulate samples, in fact, because of UV detector optics, the response is a turbidity signal read within an angle between the incident light and the photosensor (i.e., usually smaller than —10°) rather than the absorbance. This turbidity signal can be assumed to be directly proportional to the sum of all cross-sectional areas of the particulate sample components at any time. The validity of the above assumption, in the case of particles which are about 10-fold larger than the incident wavelength, is discussed elsewhere [6]. The mass frequency function can thus be expressed as [7]... 

Ultramicroelectrode Synonymous with microelectrode. Ultraviolet/visible detector, HPLC Detector for high-performance liquid chromatography that uses ultraviolet/visible absorption to monitor eluted species as they exit a chromatographic column. 

Carbon dioxide is transparent to below 190 nm, making it an ideal fluid for use with ultraviolet (UV) detectors. It can be used with acetonitrile above 195 nm and with methanol above 205 nm. The UV-vis detectors used in SFC are standard HPLC detectors in every way except for high pressure flow cells. Double tapered windows (45° bevels with matching seals) balance the stress and allow cells to be built that withstand more than 600 bar. The operator needs to be sure that the data collection rate is set fast enough to not round off the faster peaks experienced in SFC. 

Fluorescence detectors can give improved selectivity over ultraviolet absorption detectors because fewer compounds fluoresce than absorb (Chapter 16). Sensitivities at least as good as and perhaps better than the UV detector are achieved, depending on the geometry of the excitation source-detector arrangement, the intensity of the source, and the quantum efficiency of the fluorophore. The amper-ometric detector (see Chapter 15) is useful for detecting electroactive substances and has found considerable use in biological applications, for example, in the HPLC separation and detection of trace quantities of catecholamines from the brain. 

Diode array detector HPLC multichannel ultraviolet-visible detector consisting of a linear array of photodiodes onto which the full spectrum falls, i.e. 200 400 nm ultraviolet, 400-800 nm visible regions. Thus a complete spectrum can be obtained in less than 0.1 s, also several wavelengths can be monitored simultaneously to achieve maximum sensitivity for each component. 

UV detector HPLC detector based on an ultraviolet-visible spectrophotometer using microsample flow cells (10 pi). Response to components depends on their absorption spectrum and absorptivity coefficient as defined by the Beer-Lambert law. Detector wavelength is set to give maximum sensitivity ideally at Amax however an optimum wavelength, Aopt at which all the components have a satisfactory absorbance, may be used. 

Infrared Absorption Detectors. Two types of infrared detectors have been offered commercially. The first is a filter instrument similar in design to that shown in Figure 16-13. The second, and more sophisticated, type of infrared detector is based on Fourier transform instruments similar to those discussed in Section I6B-1. Several of the manufacturers of Fourier transform infrared (FTIR) instruments offer accessories that permit their use as HPLC detectors. Infrared detector cells are similar in construction to those used with ultraviolet radiation except that windows arc constructed of sodium chloride or calcium fluoride. Cell path lengths range from 0.2 to 1.0 mm and volumes from 1.5 to 10 pL. 

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