Ratio spectrum

Derivative spectrophotometric ratio spectrum-zero crossing Solid phase spectrophotometry... 

Berzas Nevado, J.J., Resolution of ternary mixtures of Tartrazine, Sunset Yellow and Ponceau 4R by derivative spectrophotometric ratio spectrum-zero crossing methods in commercial foods, Talanta, 46, 933, 1998. 

Galego and Arroyo [14] described a simultaneous spectrophotometric determination of OTC, hydrocortisone, and nystatin in the pharmaceutical preparations by using ratio spectrum-zero crossing derivate method. The calculation was performed by using multivariate methods such as partial least squares (PLS)-l, PLS-2, and principal component regression (PCR). This method can be used to resolve accurately overlapped absorption spectra of those mixtures. 

For ratioed spectra, it is of interest to ascertain the effect of the various noise sources on the ratioed spectrum (i.e., the transmittance or reflectance spectrum as the case may be), on the absorbance spectrum, and also to determine, as was done previously [1, 2, 5], the optimum value for the sample to have that will give the minimum error of the calculated value. 

Fig. 3.19 ESR spectra of the 16-PC probe in total lipid (TL) liposomes. (A) control (B) TL-nifedipine (2 1 molar ratio) (C) TL-verapamil (2 1 molar ratio). Spectrum width 6 mT. Temperature 37°C. Arrows in spectrum (A) indicate 4max determination, arrows in spectrum (C) indicate 4min. (Reprinted from Fig. 2 of ref. 68 with permission from Elsevier Science.)...

For example, in Fig. 21 the emission spectrum of a solution in which [Ru (phen)3]2+ and c/.v-DPPS are dissolved in a 1 1 ratio (spectrum c) together with the emission bands of the two components alone (a and b, respectively) are shown. The spectra have been recorded by exciting at 262 nm, that is in a region where porphyrin absorption is very weak (about 0.06 absorption units in our experimental conditions) whereas [Ru(phen)3]2+ has the strongest absorption band (about 0.4 absorption units in our experimental conditions). The emission of [Ru(phen)3]2+ alone is centred at 590 nm and, quite interestingly, is completely quenched upon the addition of an equimolar amount of c/s-DPPS. The emission of free c/.v-DPPS is much weaker than that of [Ru(phen)3]2+ because of the much lower absorbance, yet after the addition of [Ru(phen)3]2+ the porphyrin emission maintains its intensity. 

Steady-state emission spectra of a donor-acceptor labeled sample and a donor-only labeled sample are taken. The donor emission is removed from the donor-acceptor emission spectrum by subtracting the normalized donor-only emission spectrum. This leaves the fluorescence of the acceptor due to direct excitation and due to energy transfer (see Fig. 4). Clegg and co-workers call this the extracted acceptor emission spectrum, Fen,. Note that this process does not require the concentration of donor-only sample to be the same as the donor-acceptor sample—only the shape of the donor spectrum is used. This spectrum is divided by a fluorescence value (often the maximum) of an emission spectrum taken on the donor-acceptor complex excited at a wavelength where only the acceptor absorbs (565 nm for fluorescein-tetramethylrhodamine). Alternatively, one can divide by the maximum of the excitation spectrum of the donor-acceptor complex (excitation at 400-590 nm, emission in the range 580-600 nm, for fluorescein-rhodamine). In either case, the resultant ratio spectrum, (ratio), is normalized for quantum yield of acceptor, for concentration of total molecules, and for incomplete acceptor labeling. 

FIGURE 18.5 Principle of electrospray ionization and a mass-to-charge ratio spectrum of a protein. Values given are protonation charge states [41],... 

The most commonly used method for quantifying the extent of orientation in polymeric systems is the determination of the dichroic ratio. Two spectra are collected one with radiation polarized parallel to a reference direction and one perpendicular to this direction. The reference direction is most commonly chosen along the direction of orientation. The ratio of these two spectra, often called the dichroic ratio spectrum, can then be used to characterize the orientation in the system. Dichroic ratios greater... 

Diffuse reflectance is a technique usually used with FT-IR instruments. A powdered sample is placed in a small container, where source radiation strikes it and is diffusely reflected in various directions. This radiation is collected and measured by the spectrometer. Usually in the mid-IR region the finely powdered sample is diluted to 5 to 10% with finely powdered KBr or KCl. The spectrum is ra-tioed against a reference spectrum of pure powdered KBr or KCl. The ratioed spectrum is processed by a computer using a function f(Rco) derived by Kubelka and Munk, which changes the refiectance spectrum into one resembling a linear absorbance spectrum ... 

Using a KRS-5 45° crystal, (a) Reference (b) sample (c) ratioed spectrum. The spectra were recorded at 4 cm resolution using a MCT detector. 

Fig. 6.5.5 Comparison of the observed lunar ratio spectrum for Tycho/Apollo 11 with the computed blackbody ratio spectrum (Potter Morgan, 1981).

The scaling coefficients s-i and 2 are derived by calculating the ratio spectrum from the two mixtures ... 

The ratio spectrum of two of the films is shown in Fig. 3.29, and the computed pure spectra of the trans and gauche isomers are shown in Fig. 3.30. 

Spectrum a of the stationary PMMA sample was obtained with scalar decoupling but without CP and shows no observable resonances. When the stationary sample is examined by using DD and CP (spectrum b), broad resonances are observed, and these resonances reflect the effects of chemical-shift anisotropy. With the addition of MAS to the DD experiment and elimination of CP, the lines are narrowed considerably, but the signal-to-noise ratio is poor (spectrum c). Finally, with the grand experiment (MAS-DD-CP), the spectrum is resolved into the specific carbons of the PMMA molecule with good signal-to-noise ratio (spectrum d). 

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