Nonabsorbable lines

The major function of the monochromator is to separate the resonance line of the element of interest from the nonabsorbable lines which are emitted by the hollow cathode lamp. Experiments performed over a number of years indicate that, for the elements with the most complicated spectra, a resolution of 2A. is needed. (Approximate required resolution settings are shown in Table I.) For ordinary atomic absorption, there is no advantage in having better resolution. For example, a monochromator with a resolution of 0.5A. is no better for atomic absorption than one with a resolution of 2A. 

Tl. Tarasevich, N, I., and Tsalev, D. L., Selection of nonabsorbing lines for background correction in atomic absorption analysis. Vestn. Mosk. Univ., Khim. 13, 242-244 (1972). 

Two-line compensation can be used under certain circumstances. This technique makes use of a nonabsorbing line nearby in wavelength to the analysis line. It may be a line from the same source lamp or from another lamp, and absorption measurements of both lines are necessary. The absorbing line (resonance line) measurement will include absorbance due to the analyte element and also the background absorbance. Measurement on the nearby nonresonance line will produce only background absorbance. The difference between the two measurements will be the absorbance due only to the analyte element. 

The two-line method has been used successfully for nickel in oil, using the resonance spectral line at 2320 A with the nonabsorbing line at 2316 A. Lead also can conveniently be determined by this method. The method cannot be used if the two spectral lines are too far separated in wavelength, since background absorption varies with wavelength. The two-line method also requires two separate measurements taken at separate times or it requires two-channel instrumentation. The method also has limited application because of the difficulty of suitable fixed line pairs for the measurement. 

Table 6 Background correction (BC) techniques Measure absorbance at a nearby nonabsorbing line Deuterium BC Smith-Hieftje BC...

Figure 8. TEM and optical absorption of the sample implanted with 5 x 10 Au /cm (a) TEM cross-sectional micrograph (dashed lines represent the free surface and film-substrate interface) (b) nanoparticles size distribution (c) simulated optical spectra (1) Au cluster in a non-absorbing medium with n = 1.6 (2) Au cluster in polyimide (absorbing) (3) Au(core)-C(shell) cluster in a nonabsorbing medium with n = 1.6 (4) the experimental spectrum of Au-implanted polyimide sample, (d) X-ray diffraction patterns as a function of the implantation fiuence.

Figure 14.3 Absorption by gray spheres in which the absorber is uniformly distributed (upper) and by small absorbing spheres mixed with much larger nonabsorbing spheres (lower) the total amount of absorbing material is the same for both. Solid lines were calculated approximately and dashed lines connect points calculated with Mie theory.

Fig. 5 Absorption spectrum of AT DNA oligomers around 3300 cm-1 (solid line) and absorbance difference spectra for several pump-probe delay times after excitation at 1740 cm-1 (FWHM 170 cm-1). The picosecond OH stretching response of water ranges from 3600 to 3050 cm-1. The spectrum at 0 ps delay time was obtained by averaging from -200 to 200 fs to eliminate nonabsorbing signal contributions.

The design engineer often encounters the situation in which a nonblack body is surrounded completely by a large enclosure containing a nonabsorbing gas. An example would be a steam line exposed to the atmosphere. Under these conditions, little error is introduced by assuming that none of the heat radiated from the source is reflected to it, and Eq. (6) or (7) can be simplified to... 

Even the narrowest spectral bandpass obtainable with most spectrometers will not isolate the most sensitive 248.33 nm iron line from the nonabsorbing iron line at 248.42 nm and other nearby lines. Iron calibration curves, therefore, will usually be non-linear. The 302.05/302.06 nm iron line has been reported to have a better signal/noise ratio [194]. 

First line therapy for hyperammonemia is directed at reducing the production and absorption of gut-derived ammonia. Non-absorbable antibiotics are better than nonabsorbable disaccharides (e.g., lactulose) in reducing the risk of no improvement... 

If a nonabsorbing spectral line occurs within the band pass of the monochromator along with the absorbing line, useful analytical data can frequently still be obtained. The sensitivity of the determination will be reduced and a nonlinear absorbance vs. concentration calibration curve will result. 

A line filter is essentially a Fabry-Perot etalon with a very small optical path nd between the two reflecting surfaces. The technical realization uses two highly reflecting coatings (either silver coatings or dielectric multilayer coatings) that are separated by a nonabsorbing layer with a low refractive index (Fig. 4.60). For instance, for nd = 0.5 p,m the transmission maxima for vertical incidence are obtained from (4.62a) at Ai = 1 xm, A2 = 0.5 p,m, A3 = 0.33 p,m, etc. In the... 

FIGURES.9 A unique matrix referencing scheme can yield a linear K-M plot only with a nonabsorbing matrix and when plotted against a volume based measure of concentration. The log(l/i oo) curves are in general not linear. From top to bottom, the lines in each chart represent 0, 1, and 5% absorption by matrix particles. The lines represent values calculated by the representative layer theory. (Reproduced from D. J. Dahm, NIR News, 15 6-10 (2007), by permission of NIR Publications Copyright 2007.)... 

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