Second derivative spectra

Likewise, record the second derivative spectra of the four standard pseudo-ephedrine hydrochloride solutions and record the peak heights DL at 258-259 nm plot the results against concentration and confirm that a straight line is obtained. 

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. 4. ESR spectra at 298 K. A Curves 1-4 refer to CuAc, Cu-H-Y, Cu-MCM-22 and Cu-VPI-5. B Curves 1-4 refer to the second derivative spectra of curves 1-4 of A. C Curves 1-4 represent the absorption curves of CuCl,4Pc, CuCI,4Pc-Na-Y (0.26), Cu(N02)4Pc and Cu(N02)4Pc-Na-Y (0.16), respectively.

It takes a little practice to get used to looking at first-derivative spectra, but there is a distinct advantage first-derivative spectra have much better apparent resolution than do absorption spectra. Indeed, second-derivative spectra are even better resolved (though the signal-to-noise ratio decreases on further differentiation). Figure 1.6 shows the effect of higher derivatives on the resolution of a 1 2 1 triplet arising from the interaction of an electron with two equivalent 7=1/2 nuclei. 

Reeder and Rieger6 used ESR spectra to identify complex ions and to estimate formation constants for aqueous oxovanadium(iv) complexes with lactic acid, thiolactic acid, glycolic acid, and thioglycolic acid. Through the use of second-harmonic detection, which produces second-derivative spectra, the resolution was good enough that several of the individual species could be separately... 

Another variation on the fermentation of alcohol was the work done in a rice vinegar broth by Yano et al.34 Using second derivative spectra from 1600 to 1760 ran, the ethanol and acetic acid concentrations were easily determined in the culture broth. Gas chromatography was used as the reference method. 

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).

Frake et al. compared various chemometric approaches to the determination of the median particle size in lactose monohydrate with calibration models constrncted by MLR, PLS, PCR or ANNs. Overall, the ensuing models allowed mean particle sizes over the range 20-110/tm to be determined with an error less than 5 pm, which is comparable to that of the laser light diffraction method nsed as reference. Predictive ability was similar for models based on absorbance and second-derivative spectra this confirms that spectral treatments do not suppress the scattering component arising from differences in particle size. 

The use of second-derivative spectra eliminated the baseline shifts observed during the reaction (which could be due to changes in the amounts or size distribution of particles, or small amounts of probe fouling). 

Polymer type All of the polymers have very distinct, easily distinguished NIR spectra except N66 and N6 which are very similar. The use of second-derivative spectra is necessary to reliably distinguish the small spectral differences between N66 and N6. 

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. 

The performance of the NIR analyzer in static mode is shown in Table 15.3. The use of second-derivative spectra in developing the identihcation method, along with the inclusion of sufficient diversity in color and construction, allowed for 100% accurate identihcation of unknown samples. 

UV spectrum of pseudoephedrine with its first and second derivative spectra. The minima correspond to the maxima in the absorbance spectrum. 

The signahnoise ratio is poorer in the second derivative spectra because through dividing the spectrum into segments in order to calculate the derivative the underlying noise is less efficiently averaged out, which occurs when the spectrum is scanned in much narrower segments. 

FIGURE 13 Images at component-specific wavelengths and second derivative spectra of high-absorption pixel (image size 1.02cm x 1.3cm white higher absorbance, black lower absorbance). 

Figure 5. Second derivative spectra of water at different temperatures in the range from -15 to +30 °C.

Figure 9.8 Second-derivative spectra of M1 samples with different levels of water with eight data points averaging. Reprinted with permission from Zhou etal. (2003).59...

Fig. 9. Second derivative spectra for CHj.CH.C02H radicals o, at 300°K, methyl rotating, b, at 77°K, methyl in preferred orientation. (Horsfield et al., 1961a.)...

A survey of normal and derivative spectra of numerous vitamins, including vitamin Bg, has been reported. The second derivative spectra of these vitamins are especially suitable for their quantitative determinations (132). Quantitative determination by derivative spectroscopy is superior to direct spectrophotometric measurement in many problem situations. 

First-derivative spectra Second-derivative spectra... 

Figure 4.6 (a) Image from Fig. 4.5(b). (b) Image for first-derivative spectra of (a), (c) Image for second-derivative spectra of (a). 

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