UV light Fluorescence

TDM was first carried out on drags in biological samples using ultraviolet (UV) light, fluorescence, and electrochemical detection, which measured physicochemical properties of drags. Used alone, these detection methods had low sensitivity and selectivity and were soon obsolete.10... 

The short-wavelength limit for a photomultiplier is determined by the transmission of the window material covering the photocathode. Quartz can be used for tubes to be operated down to about 170 nm, and tubes with LiF windows are available to permit operation down to 105 nm. In the 30 to 300 nm region, an ordinary photomultiplier can be used by coating the quartz or pyrex entrance window with a film of sodium salicylate that, upon absorption of UV light, fluoresces with nearly unit quantum efficiency at about 400 nm. 

Direct Optical Evaluation With 365-nm UV Light (Fluorescence Measurement)... 

High-performance liquid chromatographic (HPLC) procedures using reversed-phase columns and detection by ultraviolet (UV) light, fluorescence detection (FED),... 

MP-suspension by automated ASTM-bulb Magnetization current by Hall-Sensor Magnetization time UV-Light intensity All Liquids (fluorescence, contamination) Process times and temperatures Function of spraying nozzles, Level of tanks Flow rates (e.g. washing, water recycling) UV-Light intensity... 

Photodegradation as well as fluorescence quenching has been observed in chlorophyll monolayers [302,316]. Whitten [317] observed a substantial decrease in the area of mixed films of tripalmitin and a ci5-thioindigo dye as isomerization to the trti 5-thioindigo dye occurred on irradiation with UV light. 

LIF is also used witii liquid and solid samples. For example, LIF is used to detect lJO ions in minerals the uranyl ion is responsible for the bright green fluorescence given off by minerals such as autunite and opal upon exposure to UV light [23],... 

Fluorescence Microscope. A useful light microscope utilizes UV light to induce fluorescence in microscopic samples (40). Because fluorescence is often the result of trace components in a given sample rather than intrinsic fluorescence of the principal component, it is useful in the crime laboratory for the comparison of particles and fibers from suspect and crime scene. Particles of the same substance from different sources almost certainly show a different group of trace elements. It is also very useful in biology where fluorescent compounds can be absorbed on (and therefore locate and identify) components of a tissue section. 

Colorimetric and Fluorimetric Analysis. The functional groups of amino acids exhibit Htde absorption of uv light from 210 to 340 nm where uv absorption spectrometry is most conveniently conducted. Thus color or fluorescence formation reactions are employed for amino acid detection (128). 

Colorless substances absorb at wavelengths shorter than those of the visible range (the UV range normally amenable to analysis X = 400...200 nm). Such compounds can be detected by the use of UV-sensitive detectors (photomultipliers. Sec. 2.2.3.1). Substances that absorb in the UV range and are stimulated to fluorescence or phosphorescence (luminescence) can be detected visually if they are irradiated with UV light. 

Fluorescent and phosphorescent substances are excited into an unstable energy state by UV light. When they return to the ground state they release a part of the energy taken up in the form of radiation. The emitted radiation is less energetic than the light absorbed and usually lies in the visible part of the spectrum. Since absorption (excitation) and emission obey a linear relationship over a certain range a reduction in absorption leads to a reduction in the luminescence, too. 

This property can be applied to the detection of substances that absorb in the UV region For on layers containing a fluorescent indicator or impregnated with a fluorescent substance the emission is reduced in regions where UV-active compounds partially absorb the UV light with which they are irradiated. Such substances, therefore, appear as dark zones on a fluorescent background (Fig. 4A). 

These restrictions do not apply to the less intense fluorescent tubes installed in the UVIS or MinUVIS (Fig. 6) or Universal UV lamps (Fig. 7). Black glass surrounds or screens serve as filters. Unfortunately account is often not taken of the fact that the transparency for short-wavelength UV light decreases appreciably with increasing duration of irradiation (Fig. 8). So it is advisable to change the filters of lamps intended for short-wavelength radiation at regular intervals. They can... 

Substances that are intrinsically fluorescent can often be exeited with long-wavelength UV light. They absorb the radiation and then emit, usually in the visible region of the spectrum, so that they appear as bright luminous zones, whieh can frequently be differentiated by color. They, thus, set themselves apart from the multitude of substances that only exhibit absorption. This detection possibility is characterized by high specificity (Sec. 2.3). 

Primary and secondary amines, amino acids and phenols react In the case of long-wavelength UV light (A = 365 nm) the DANS amides fluoresce yellow-green, while amines that have reacted at a phenolic OH group have an intense yellow to yellow-orange fluorescence The detection hmit for DANS amides is ca 10 mol [86]... 

Aluminium oxide deoxynivalenol in wheat 7 mm at 120 °C, yields a fluorescent derivative under UV light (i = 365 nm) [193, 196]... 

After the dipped or sprayed chromatogram has been dried in a stream of cold air long-wave UV light (2 = 365 nm) reveals fluorescent yellow zones (flavonoids). Sterigmatocystine, which can be detected without derivatization on account of its red intrinsic fluorescence (detection limit 0.5 pg), also fluoresces pale yellow after being heated to 80°C [9] or 100°C [13] for 10 min on the other hand, citrinine, zearalenone and vomitoxin fluoresce blue. 

The chromatogram is freed from mobile phase and immersed for 1 s in the freshly prepared reagent solution and then heated to 105 to 110 °C for 5 to 10 min. Green, blue or purple fluorescence appears on a dark background under long-wavelength UV light (2 = 365 nm). 

Grey-green zones on a white background resulted they exhibited weak red fluorescence under long-wavelength UV light (X = 365 nm) glucose and fructose exhibited pale blue fluorescence in method B. Some hRf values are listed in Table 1. 

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