Monochromatic filter

When the fluorescence method becomes more generally adopted, it will be necessary to study not only those factors (neutral salt, temperature) which alter the equilibrium relationships, but also those which influence fluorescence (deformation effect, influence of solvent, etc. cf. P. W. Danckwortt, Luminescence Analysis, 2 Ed., Leipzig 1929 F. Weigebt, Optical Methods in Chemistry, 1927). The interesting publication of L. J. Desha should be consulted regarding the quantitative aspects of fluorometry. In quantitative work it is best to use the filtered monochromatic ultraviolet radiation (X = 366 mm) from a quartz lamp. Con-... 

Figure 3 Principle of a foam film microinterferometry cell. Single, thin liquid films are formed above a bubble attached to an air-water surface in a tightly closed cell placed in the field of a metallographic microscope (x 200). and illuminated by reflected heat-filtered monochromatic light. The microscope can be focused either on the film or on the bubble diameter. The interferometry patterns change with the film local thickness. In Figures 4 -6, the bubble diameter is 1.21 mm and the film diameter is 0.42 mm...

In contrast to spectrophotometry, hght-scattering experiments are generally conducted at constant wavelength. Mercury vapor lamps are the most widely used light sources, since the strong lines at 436 and 546 nm are readily isolated by filters to allow monochromatic illumination. Polarizing filters are also included for both the incident and scattered beams so that depolarization can... 

Until the advent of lasers the most intense monochromatic sources available were atomic emission sources from which an intense, discrete line in the visible or near-ultraviolet region was isolated by optical filtering if necessary. The most often used source of this kind was the mercury discharge lamp operating at the vapour pressure of mercury. Three of the most intense lines are at 253.7 nm (near-ultraviolet), 404.7 nm and 435.7 nm (both in the visible region). Although the line width is typically small the narrowest has a width of about 0.2 cm, which places a limit on the resolution which can be achieved. 

Additions to the PLM include monochromatic filters or a monochromator to obtain dispersion data (eg, the variation in refractive index with wavelength). By the middle of the twentieth century, ultraviolet and infrared radiation were used to increase the identification parameters. In 1995 the FTIR microscope gives a view of the sample and an infrared absorption pattern on selected 100-p.m areas (about 2—5-ng samples) (37). 

Photomultipliers are appreciably more sensitive sensors than the eye in their response to line or continuum sources. Monochromators are fitted to the light beam in order to be able to operate as substance-speciflcally as possible [5]. Additional filter combinations (monochromatic and cut-off filters) are needed for the measurement of fluorescence. Appropriate instruments are not only suitable for the qualitative detection of separated substances (scanning absorption or fluorescence along the chromatogram) but also for characterization of the substance (recording of spectra in addition to hR and for quantitative determinations. 

Cut off filters are employed to ensure that none of the excitation radiation can reach the detector. Monochromatic filters are used to select particular spectral... 

In long-wavelength UV light (2 = 365 nm) carbohydrates, e.g. glucose, fructose and lactose, yield pale blue fluorescent derivatives on a weakly fluorescent background. In situ quantitation can be performed at = 365 nm and 2fi = 546 nm (monochromatic filter M 546) [19]. Further differentiation can be achieved by spraying afterwards with p-anisidine-phosphoric acid reagent [8]. 

In situ quantitation The fluorimetric determination was carried out under long-wavelength UV light (/leic = 365 nm, Xn = 546 nm, monochromatic filter Fig. 1). 

Unlike the carbon monoxide measuring instrument discussed above, the Lion Intoximeter 3000 uses an interference filter to produce monochromatic radiation... 

To summarize Filtering is an effective way of producing intense monochromatic beams, but it is severely limited because it cannot be used at all wavelengths and cannot achieve high spectral purity at any wavelength. The analysis of a spectrum, that is, the selection of a line and the measurement of its intensity, requires Bragg reflection. 

Bragg reflection (1.14) can accomplish, as filtering (4.6) cannot, both monochromatization and spectral analysis. With a well-collimated beam, this can be done with a flat crystal, though not without further losses in intensity. 

For the purposes of analytical chemistry, four kinds of monochromatic beams need to be considered. (The quotation marks are to remind the reader that the beams under discussion are not always truly monochromatic.) Three kinds of beams—those produced by Bragg reflection (4.9), filtered beams (4.6), beams in which characteristic lines predominate over a background that can be neglected— will be discussed later ( 6.2). The fourth kind of beam contains monochromatic x-rays that are a by-product of our atomic age and that promise to grow in importance they are given off by radioactive isotopes. These x-rays must not be confused with 7-rays (11.1), which also originate from radioactive atoms but which differ from x-rays because the transformation that leads to radiation involves the nucleus. 

As indicated above, absorption effects can generally be predicted and satisfactorily estimated when only monochromatic x-rays are involved. When a polychromatic beam is used for excitation, the filtering of the beam by the sample complicates the situation and modifies the absorption effects. Even then, fairly reliable estimates of the effects can be made. 

Funk et al. have used a low-pressure mercury lamp without filter to liberate inorganic tin ions from thin-layer chromatographically separated organotin compounds these were then reacted with 3-hydroxyflavone to yield blue fluorescent chromatogram zones on a yellow fluorescent background [22]. Quantitative analysis was also possible here (XoK = 405 nm, Xji = 436 nm, monochromatic filter). After treatment of the chromatogram with Triton X-100 (fluorescence amplification by a factor of 5) the detection limits for various organotin compoimds were between 200 and 500 pg (calculated as tin). 

In situ quantitation For fluorimetric evaluation there was excitation at = 313 nm and the fluorescence emission was measured at = 365 nm (monochromatic filter M 365). This arrangement yielded the most intense signals. (The emission beam at X, = 365 nm is appreciably more intense than the visible yellow fluorescence.) Further treatment of the chromatogram with liquid paraffin - -hexane (1+2) is not to be recommended. 

Fig. 1 Comparison of the detection sensitivity after derivatization of three purine derivatives with chloramine T - sulfuric acid (A) and chloramine T - hydrochloric acid (B). Measurement X. (. = 365 nm, A.(, = 440 nm (monochromatic filter M 440) 1 = theophylline, 2 = theobromine, 3 = caffeine.

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