Detector ultraviolet

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. 

Because of the potential hazard of release of unignited hydrocarbons at ground level, a flame scanner with alarm in the control house is included for each pilot. The flame scanner must be located so that interference of ultra violet rays from the main flame or other sources do not cause false readings. Ultraviolet detectors should be mounted such that they are looking straight down through the pilots toward the ground. The installation should also provide strainers in each gas or oil line to pilots. 

If unidentified peaks are detected the stability of the protein under the chromatographic conditions should be checked. In all analytical investigations of proteins on SEC columns it is desirable to be able to monitor the eluted peaks at a very high sensitivity of the ultraviolet detector. Therefore, very pure (analytical grade) salts and buffers should be used. 

These combined HDF and GPC separations require the use of detectors such as static light scattering or viscometers to help sort out the convoluted elution profiles seen in those type of experiments. It should also be remembered in these situations that the typical refractive index or ultraviolet detector responses may not be representative of the actual mass fraction of insolubles eluting from the column because of the significant light scattering that can occur with those large particles in the detector cell. 

Despite their higher sensitivity and relative cheapness compared with ultraviolet detectors, amperometric detectors have a more limited range of applications, being often used for trace analyses where the ultraviolet detector does not have sufficient sensitivity. 

A stainless steel column (4.6 mm internal diameter by 250 mm length) packed with 4 micron Zorbax Octadecylsilane (ODS) (Dupont) was equilibrated with 78 % acetonitrile in water at a flow rate of 2.0 ml/min provided by a Spectraphysics, model 8700, pump and controller. The effluent was monitored at 215 nm using a Jasco Uvidec 100 V ultraviolet detector. Peaks were recorded and calculations performed by a Spectraphysics recording integrator, model 4270. Samples, containing 5 mg/ml of material dissolved in p-dioxane, were applied to the column automatically with a Micromeritics autosampler, model 725, equipped with a 10 microliter loop. Some analyses were performed on a Hewlett-Packard HPLC, model 1090, equipped with a diode array detector. 

By far, the most frequently used device is the ultraviolet detector. Three types are employed (23) — single wavelength with low pressure mercury source, multiwavelength filter photomer with medium pressure mercury source, and spectrophotometer. 

Headspace analysis has also been used to determine trichloroethylene in water samples. High accuracy and excellent precision were reported when GC/ECD was used to analyze headspace gases over water (Dietz and Singley 1979). Direct injection of water into a portable GC suitable for field use employed an ultraviolet detector (Motwani et al. 1986). While detection was comparable to the more common methods (low ppb), recovery was very low. Solid waste leachates from sanitary landfills have been analyzed for trichloroethylene and other volatile organic compounds (Schultz and Kjeldsen 1986). Detection limits for the procedure, which involves extraction with pentane followed by GC/MS analysis, are in the low-ppb and low-ppm ranges for concentrated and unconcentrated samples, respectively. Accuracy and precision data were not reported. 

Figure 1 Ultraviolet spectra for benzaldehyde and benzoic acid solvent, methanol reference, methanol cell, 1.0 cm. (From Pfeiffer, C. D., Larson, J. R., and Ryder, J. F., Linearity testing of ultraviolet detectors in liquid chromatography, Anal. Chem., 54, 1622, 1983. Copyright American Chemical Society Publishers. With permission.)...

Varma [106] determined iodide in seawater in amounts down to 2 mg/1 by a method based on pre-column derivatisation of the iodide into 4-iodo-2,6-di-methyl phenol. An ultraviolet detector was employed. 

Applications. Ultraviolet detectors are ideally suited for applications where rapidly developing fire can occur in a relatively open area. UV detectors can be used to monitor ammunition assembly lines, gunpowder troughs, or open areas that are stocked with hazardous materials. These detectors are not typically affected by extremes of temperature or pressure, adverse weather conditions, high humidity, nor are they sensitive to solar radiation. 

It must also be noted that since the ultraviolet detector is an optical device, objects that are able to block its view cannot be allowed to come between the detector and the area to be protected. 

When properly applied, ultraviolet detectors can serve as excellent fire detectors in munitions manufacturing. Detection times as fast as 10 milliseconds can be achieved while effectively resisting false alarms. 

Advantages. Like ultraviolet detectors, infrared detectors have their advantages and limitations. Several advantages of IR units make them valuable in certain installations ... 

All of the ionizing air systems at Longhorn are located in areas where ultraviolet sensors are used in conjunction with deluge systems for fire protection. Care must be taken to shield the ultraviolet detectors from the ion generating corona source. The systems used at Longhorn are individually shielded with PVC tubing or with hoods. 

HCN = hydrogen cyanide HPLC = high performance liquid chromatography NaOH = sodium hydroxide GC = gas chromatography ECD = electron capture detector NPD = nitrogen-phosphorus detector UV = ultraviolet detector. 

Lanina et al. 1992 Oishi 1990). These methods include gas chromatography (GC) combined with mass spectrometry (MS) and high-performance liquid chromatography (HPLC) combined with an ultraviolet detector (UV). No comparisons can be made between methods since no data were given regarding sensitivity, recovery, or precision. 

GC = gas chromatography HC1 = hydrochloric acid HPLC = high-performance liquid chromatography MS = mass spectrometry Na2S04 = sodium sulfate NR = not reported UV = ultraviolet detector... 

The nitrobenzene oxidation mixture was analyzed using the HPLC method. 0.2 mL of the stock solution was pipetted into a 25 mL volumetric flask and acetonitril-water (1 2 vA ) was added to it. About 20 gL of the sample solution was next injected into the HPLC system (Shimatzu) equipped with a Hypersil bond C,g coluitm (particle size 5 gL, 25 x 4.6 mm i.d.) to quantitatively determine the vanillin component while another component was determined qualitatively. Acetonitril-water (1 8) containing 1% acetic acid was used as an eluent with a flow rate of 2 tuL/min. The eluent was then monitored with an UV (ultraviolet) detector at 280 ran [6]. 

A high-performance liquid chromatography system can be used to measure concentrations of target semi- and nonvolatile petroleum constituents. The system only requires that the sample be dissolved in a solvent compatible with those used in the separation. The detector most often used in petroleum environmental analysis is the fluorescence detector. These detectors are particularly sensitive to aromatic molecules, especially PAHs. An ultraviolet detector may be used to measure compounds that do not fluoresce. 

The separation of a mixture of aromatic compounds (benzene, naphthalene, anthracene, chrysenes, and benz(a)pyrene) at 31 bar is shown in Figure 3. This chromatogram was obtained with a Perkin Elmer Model 250 ultraviolet detector with the high-pressure cell placed after the cooling heat exchanger and before the flow control valve. A similar chromatogram is obtained with an Isco Model UAA with a 10 mm micro cell placed after the flow control valve. 

Nitrogen-phosphorus detection PC = Photoconductivity TEA = Thermal energy analyzer UV = Ultraviolet detector... 

B. K. Meyer, Magnetic Resonance Investigations on Group Ill-Nitrides M. S. Shur and M. Asif Khan, GaN and AlGaN Ultraviolet Detectors... 

Razeghi M, Rogalski A (1996) Semiconductor ultraviolet detectors. J Appl Phys 79 7433... 

HPLC system with an ultraviolet detector (254 nm) and a nonporous poly-(styrene-divinylbenzene) particle based Ci8 reversed-phase column, DNASep (Transgenomic, Omaha, NE, USA). 

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). 

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