Fluorescence spectroscopy filters

Dunn and Stich [78] and Dunn [79] have described a monitoring procedure for polyaromatic hydrocarbons, particularly benzo[a]pyrene in marine sediments. The procedures involve extraction and purification of hydrocarbon fractions from the sediments and determination of compounds by thin layer chromatography and fluorometry, or gas chromatography. In this procedure, the sediment was refluxed with ethanolic potassium hydroxide, then filtered and the filtrate extracted with isooctane. The isooctane extract was cleaned up on a florisil column, then the polyaromatic hydrocarbons were extracted from the isoactive extract with pure dimethyl sulphoxide. The latter phase was contacted with water, then extracted with isooctane to recover polyaromatic hydrocarbons. The overall recovery of polyaromatic hydrocarbons in this extract by fluorescence spectroscopy was 50-70%. 

In the other study. X-ray fluorescence spectroscopy was used to analyze trace element concentrations by observing dusts on 37 ram diameter cellulose acetate filters (20). Twenty-three elutriator and twenty-three area samples from 10 different bales of cotton were analyzed. The average fraction of total dust accounted for by the elements analyzed was 14.4% amd 7.6% for vertical elutriator and area samples, respectively. Although the variation in absolute quantity of atn element was high, the relative abundance of an element was consistent for measurements within a bale. Averaged over all the samples analyzed, calcium was the most abundant element detected (3.6%), followed by silicon (2.9%), potassium (2.7%), iron (1.1%), aluminum (1.1%), sulfur (1.0%), chlorine (0.8%) and phosphorous (0.6%). Other elements detected in smaller aunounts included titanium, manganese, nickel, copper, zinc, bromine, rubidium, strontium, barium, mercury amd lead. 

Brown and Bern (26) cinalyzed the elemental composition of four card room dusts using X-ray fluorescence spectroscopy. Two of these were from filter cake material collected in two textile mills from which fine dusts (<20 ym) were separated by mechanical agitation (sonic sifting). The third sample was from filter cake material collected in a textile mill from which dust was removed by hexane washing followed by sonification of the bath, filtration and further sonification. The fourth sample came from dust collected on an electrostatic precipitator in a model card room. Results are shown in Table VI. 

Shaw also describes two techniques that now make it possible to analyze particles without removing them from collection filters. To determine the mass of a sample, technicians insert the particle-laden filter between a source that emits beta particles and a detector that counts them. As the mass increases, the number of particles that can penetrate the sample decreases. To determine the atomic elements in a specimen, laboratory workers may also separately carry out x-ray fluorescence spectroscopy. X-rays passed through the sample cause each element to emit charactenstic x-rays. The energy levels of the rays reveal the identity of the elements the intensity of the x-rays (number emitted) reflects the concentrations. 

Experimental Setup. The instrumentation (both optics and electronics) for studying saturated laser induced fluorescence spectroscopy is much less conplicated than for CARS. The experimental setup shown in Figure 18, as used in our laboratory, is typical for these studies. In some experiments it is advantageous to use a monochromator rather than band pass filters to isolate the laser induced fluorescence signal. The lasers used are either flash lamp pumped systems or NdsYAG pumped dye lasers. 

Fluorescence Spectroscopy and Test. Fluorescence Spectroscopy is the branch of visible spectroscopy dealing with fluorescence In conducting a test, the object to be studied (such as an inorg or organic specimen) is shielded from extraneous light and is then illuminated with an ultraviolet lamp (such as a quartz mercury lamp), covered with a filter to remove visible radiation. If the sample glows (fluoresces), the spectrum of this glow is studied by spectroscope and this permits the establishment of the identity of the sample... 

Fluorescence quantum efficiencies of several solid materials have been measured by photoacoustic spectroscopy." The photophysics of quantities for some common fluorescence standards have been made with some accuracy the influence of refractive index corrections on yield and lifetimes are discussed, 9,10-diphenylanthracene, quinine bisulphate, and 2-aminopyridine being the selected examples. Correction for inner filter effects in fluorescence spectroscopy have been proposed. ... 

Lasing can be sustained over a continuous range of wavelengths on the order of 40 to 50 nm. The broad band over which lasing occurs makes the dye laser suitable for tuning by inserting a grating, a filter, a prism, or an interferometric element into the laser cavity. Dye lasers are very useful for molecular fluorescence spectroscopy and many other applications. 

Off-line systems are typically used for the detection of the metal analytes occurring in the atmosphere as particulates or fumes which, after collection by an appropriate filter, are subjected to dry ashing followed by acid decomposition [63] or, more commonly, wet ashing [63], and quantitation by ICP-AES [64], flame AAS [65], normal or furnace AAS [66,67], or X-ray fluorescence spectroscopy [68]. Oguma and van Loon [69] reported a method for the... 

Suggest why A < 0.2 is recommended to minimize inner filter effects in fluorescence spectroscopy using a standard I cm pathlength cuvette. (Hint calculate the % transmission.)... 

In excited-state spectroscopies, including fluorescence spectroscopy, wavelength is accurately an SLI variable only in the limit of low absorbance. With typical specimen geometry, an absorbance of 0.02 gives a nonlinearity of approximately 2%, so that either specimen absorbance should be less than 0.02 at all wavelengths used or else this inner filter effect should be carefully corrected. In fluorescence spectroscopy, Raman scattering is a signal that does not obey a multilinear model ... 

In low-level fluorescence spectroscopy or Raman spectroscopy, the scattered light of the intense exciting laser often overlaps the fluorescence lines. Here special interference filters are available which have a narrow minimum transmission at the laser wavelength (line-blocking filter) but a high transmission in the other spectral ranges. 

Flnorescence spectroscopy, although not a new teclmique, is stiU, compared to other analytical methods, relatively immature in terms of standardization of measurement. As mentioned in Chapter 1, the birth of fluorescence spectroscopy was marked by the work of Sir George Gabriel Stokes, who in 1852 reported his studies on quinine bisulfate using what today would be considered a filter fluorimeter arrangement, as shown in Figure 5.1. 

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