Second derivative absorption spectra

Mantini A R, Marzocchi M P and Smulevich G 1989 Raman excitation profiles and second-derivative absorption spectra of beta-carotene J. Chem. Phys. 91 85-91... 

Because of peak overlappings in the first- and second-derivative spectra, conventional spectrophotometry cannot be applied satisfactorily for quantitative analysis, and the interpretation cannot be resolved by the zero-crossing technique. A chemometric approach improves precision and predictability, e.g., by the application of classical least sqnares (CLS), principal component regression (PCR), partial least squares (PLS), and iterative target transformation factor analysis (ITTFA), appropriate interpretations were found from the direct and first- and second-derivative absorption spectra. When five colorant combinations of sixteen mixtures of colorants from commercial food products were evaluated, the results were compared by the application of different chemometric approaches. The ITTFA analysis offered better precision than CLS, PCR, and PLS, and calibrations based on first-derivative data provided some advantages for all four methods. ... 

Fig. 3.44 Second-derivative absorption spectra oflOpM 4-hydroxytamoxifen in DMPC liposomes at different lipid concentrations. The nominal concentration of DM PC in suspensions was 0 (curve 0), 21 (1), 28 (2), 42 (3),...

Figure 7.15. Typical second-derivative absorption spectra of gaseous samples. A Spectrum of an automobile exhaust. B Spectrum of 14 ppm benzene. Spectra courtesy of Lear Siegler Inc., Environmental Technology Division, Englewood, Colorado.

Absorption Spectroscopy. Second derivative absorption spectra were recorded using a Perkin-Elmer Model 554 absorption spectrophotometer. Film samples were analysed by transmission on optically transparent quartz flats. 

Figure Bl.4.7. Top THz generation by optical-heterodyne conversion in low-temperature GaAs. (a) The three DBR laser system that synthesizes a precise difference frequency for the THz photomixer spectrometer, (b) the MOPA system and the set-up for spectroscopy. Bottom second-derivative absorption spectrum of the...

Figure 1.3Sc. Second derivative absorption spectrum of 13 pM ct acid glycoprotdn in bufler at pH 7.

Figure I 36a. Second derivative absorption spectrum from 245 and 270 nm of 13 pM ai-acid glycoprotein in bulTer at pH 7...

One group has successfiilly obtained infonnation about potential energy surfaces without measuring REPs. Instead, easily measured second derivative absorption profiles are obtained and linked to the fiill RRS spectrum taken at a single incident frequency. In this way, the painstaking task of measuring a REP is replaced by carefiilly recording the second derivative of the electronic absorption spectrum of the resonant transition [, 59],... 

Figure 7.3 shows the chromatogram and the spectra of standard CLA from Matreya (Pleasant Gap, PA) by analyzing the UV spectrum, it is possible to discriminate among CLA geometrical isomers, Z,E, E,E Z,Z, with an increasing maximum of absorption in the order E,Esecond-derivative UV spectrum (12) is an additional tool that can be used to confirm the presence of the CD system in the eluted fatty acid. 

The influence of an impurity (Y) on the absorption spectrum of a substance (X) can often be eliminated by considering derivative curves as shown in Fig. 17.15 the second-order plot of the mixture is identical with that of pure X. When the interference spectrum can be described by an nth-order polynomial, the interference is eliminated in the (n+ 1) derivative. 

Actifed is a medicinal preparation in which the effective components are the two drugs pseudoephedrine hydrochloride and triprolidine hydrochloride. The absorption spectrum of Actifed tablets dissolved in 0.1M hydrochloric acid is similar to that shown in Fig. 17.14(a) which is clearly of no value for quantitative determinations. A second derivative spectrum however is similar in character to that shown in Fig. 17.14(6) in which peak C corresponds to the pseudoephedrine hydrochloride and D to the triprolidine hydrochloride and from which it is possible to make quantitative measurements. Experience showed that it is advisable to use different response times for the two peaks with the instrument used a response setting of 3 was found to give the best results for pseudoephedrine hydrochloride, whilst a setting of 4 was best for the triprolidine hydrochloride. 

In most cases, you will use the first harmonic and the normal first-derivative of the absorption spectrum will be presented. If your spectrum has very good S/N and has some regions where you would like better resolution, a second-derivative presentation may help. However, second derivatives from second harmonic detection are very costly in terms of S/N ratio and so you really do have to have a strong signal ... 

FIGURE 6.1 Integration of an EPR spectrum. The EPR derivative spectrum of the hydrated copper ion (trace A) is numerically integrated to its EPR absorption spectrum (trace B) and a second time integrated (trace C) to obtain the area under the absorption spectrum. Note that both the derivative and the absorption spectrum start and end at zero, while the doubly integrated spectrum levels off to a constant value the second-integral value. 

Fig.7. Quadratic Stark effect spectrum of a poly(methylmetacrylate) film doped with an azobenzene-linked amphiphile C180AZ0C00H (solid line). Dotted line, broken line, and dash and dotted line show an absorption spectrum of the film, its first derivative, and second derivative, respectively.

The previous sensitivity can be still improved by calculating the second derivative spectrum that is, (OD)lddf versus A,. Figure 1.6 is a nice example of this improvement. It shows the room temperature absorption spectrum of a natural colorless... 

Figure 1.6 The absorption spectrum and first and second derivative spectra of a natural colorless diamond. The marked wavelengths indicate characteristic bands of N3 centers (reproduced with permission from Lifante et at., 1990).

Construction effects The effects of construction were less pronounced than the effects of color. In general, cut pile carpets had larger absorbances across the entire spectrum than did loop pile carpets, but the positions of the characteristic absorption peaks were not affected. As for color, accurate calibration models could be developed on second-derivative spectra as long as sufficient variation in carpet construction was included in the library. 

A typical hyperfine spectrum is shown in Fig. 1 in which the spectrum of an aqueous solution of K3Mo(CN)8 is given. This spectrum is a plot of the first derivative of the absorption curve as a function of the magnetic field, the frequency being held constant. (Most ESR spectra are displayed as the first derivative of the absorption, although some workers are now plotting the second derivative instead.) Seventy-five per cent of the molybdenum atoms are isotopes with no nuclear spin, whereas 25 per cent are the isotopes... 

In the second derivative spectrum of water shown in Figure 5, three absorption bands which are associated with S0, S, and S2 species, respectively were observed [6]. As temperature decreases, absorbance of S0 decreases, while absorbance of S, and S2 increases. 

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