Diffuse reflection spectra

A solvent free, fast and environmentally friendly near infrared-based methodology was developed for the determination and quality control of 11 pesticides in commercially available formulations. This methodology was based on the direct measurement of the diffuse reflectance spectra of solid samples inside glass vials and a multivariate calibration model to determine the active principle concentration in agrochemicals. The proposed PLS model was made using 11 known commercial and 22 doped samples (11 under and 11 over dosed) for calibration and 22 different formulations as the validation set. For Buprofezin, Chlorsulfuron, Cyromazine, Daminozide, Diuron and Iprodione determination, the information in the spectral range between 1618 and 2630 nm of the reflectance spectra was employed. On the other hand, for Bensulfuron, Fenoxycarb, Metalaxyl, Procymidone and Tricyclazole determination, the first order derivative spectra in the range between 1618 and 2630 nm was used. In both cases, a linear remove correction was applied. Mean accuracy errors between 0.5 and 3.1% were obtained for the validation set. 

Artifact removal and/or linearization. A common form of artifact removal is baseline correction of a spectrum or chromatogram. Common linearizations are the conversion of spectral transmittance into spectral absorbance and the multiplicative scatter correction for diffuse reflectance spectra. We must be very careful when attempting to remove artifacts. If we do not remove them correctly, we can actually introduce other artifacts that are worse than the ones we are trying to remove. But, for every artifact that we can correctly remove from the data, we make available additional degrees-of-freedom that the model can use to fit the relationship between the concentrations and the absorbances. This translates into greater precision and robustness of the calibration. Thus, if we can do it properly, it is always better to remove an artifact than to rely on the calibration to fit it. Similar reasoning applies to data linearization. 

Very few studies on complexes of palladium and platinum with 1,1-dithiolato ligands have been reported recently. The electronic absorption spectra of the Et2dtc complexes of Pd and Pt, as well as Zn, Cu, Fe, Co, and Mn, have been measured in MeCN, EtOH, and -heptane, with diffuse-reflectance spectra also being determined (401). In 1969 and... 

Fig. 1. UV-vis diffuse reflectance spectra of neat Ti02, chemically-modified and Ti02-loaded MCM-...

UV diffuse reflectance spectra of the titanates were obtained with a JASCO UVIDEC-660 spectrophotometer using a sintered alumina disc as a reference. Raman spectra were recorded at room temperature on a JASCO NR-1100 spectrometer. 

Figure 4. UV diffuse reflectance spectra of BaTi409(-Ba4Tii303o(—) ...

Ultraviolet-visible (UV-vis) diffuse reflectance spectra of supported WOx samples and standard W compounds were obtained with a Varian (Cary 5E) spectrophotometer using polytetrafluoroethylene as a reference. The Kubelka-Munk function was used to convert reflectance measurements into equivalent absorption spectra [12]. Spectral features of surface WOx species were isolated by subtracting from the W0x-Zr02 spectra that of pure Z1O2 with equivalent tetragonal content. All samples were equilibrated with atmospheric humidity before UV-vis measurements. 

Fig. 3. Diffuse reflection spectra of nominally pure MgTijOj (O) and of MgTi205 M(II). The nature of M is indicated...

Samples were characterized by FTIR spectroscopy with a Perkin Elmer (Spectrum BX) spectrometer using KBr pressed disks as matrices. The DRIFT experiments were carried out with a Broker IFS 55 spectrometer equipped with a Thermo Spectra Tech reacting cell. UV-vis Diffuse Reflectance spectra were recorded on a Perkin Elmer Lambda 45 spectrophotometer equipped with a diffuse reflectance attachment. Raman spectra were collected with Perkin Elmer system 2000 NIR FT-Raman using as excitation radiation the 5th harmonic of a diode pumped Nd YAG laser (1065 nm). 

Fig-1 Absorption spectra, obtained through the Kubelka-Munk transformation of diffuse reflectance spectra, of indolinonaphthospiropyran adsorbed onto silica gel. Spectra are shown for coverages of (A) 2.35, (B) 9.49, (C) 34.2, and (D) 46.7 /ig/m2. (Data adapted from Ref. 12.)... 

Fig. 5 Diffuse reflectance spectra of 6-nitrobenxospiropyran (A) in pure form and (B) after its sorption onto silicic acid. (Data adapted from Ref. 35.)...

Fig. 36. UV-visible diffuse reflectance spectra and elemental analysis data for Ti-SBA-15 (1) sample 1 (2) sample 2 (3) sample 3 and (4) sample 1 after treatment with 30% H202 [from Trukhan et al. (234)].

Fig. 50. Diffuse reflectance spectra recorded (a) before and (b) after 20 min of thermal reaction of propene in TS-l/TiOOH molecular sieve at room temperature [Reprinted from Lin and Frei (133) with permission. Copyright (2002) American Chemical Society].

The experimental methods which give informations on the structure of the phases (for example, x-ray diffraction analysis of polycrystalline substances, diffuse reflectance spectra) may be used to follow the kinetics of solid-solid reactions. 

Analogously, when a colourless aqueous solution of quinolinium chloride (Q+ CP) is mixed with an almost colourless aqueous solution of Na+V(CO)p the well-formed dark green crystals of the vanadate salt precipitate immediately. In each case, the spontaneous separation of the highly coloured salts is made even more dramatic by the absence of colour in the aqueous mother liquors throughout the course of precipitation. The quantitative effects in these coloured salts are observed as broad absorption bands in the spectral region between 350 to beyond 700 nm when they are dissolved in dichloromethane, or in the diffuse reflectance spectra of the crystalline salts. The correspondence of the band maximum (Act) and... 

Barnes, R. J., Dhanoa, M. S., Lister, S. J. Appl. Spectrosc. 43,1989, 772-777. Standard normal variate transformation and de-trending of near-infrared diffuse reflectance spectra. Barnes, R. J., Dhanoa, M. S., Lister, S. J. J. Near Infrared Spectrosc. 1, 1993, 185-186. Correction of the description of standard normal variate (SNV) and De-Trend transformations in practical spectroscopy with applications in food and beverage analysis. Brereton, R. G. Chemometrics—Data Analysis for the Laboratory and Chemical Plant. Wiley, Chichester, United Kingdom, 2006. 

Fig. 7.13 UV-VIS diffuse reflectance spectra of modified and pure samples (a) Ti02, (b) C Ti02, (c) physical mixture of Ti02 and hydrothermal carbon and (d) pure carbon.

Recently, a large anionic pigment has been intercalated into an LDH host by ion-exchange of an Mg/Al LDH nitrate precursor with a solution of C.I. Pigment Red 48 2 (the calcium salt of 4-((5-chloro-4-methyl-2-sulfophenyl)azo)-3-hydroxy-2-naphthalene-carboxylic acid), in ethane-1,2-diol [215]. The UV-visible diffuse reflectance spectra of C.I. Pigment Red... 

Figure 12.6 The effect of Savistky-Colay first and second derivative preprocessing on a set of NIR diffuse reflectance spectra (A) the raw (uncorrected) spectra, (B) spectra after Ist derivative preprocessing, (C) spectra after 2nd derivative preprocessing. In both cases the window width was 15 points (7.5 nm), and the polynomial order was 2.

Figure 12.7 shows the results obtained when MSC preprocessing (using the mean as the reference spectrum) is applied to the same NIR diffuse reflectance spectra that were shown previously. Note that both SNV and MSC accomplish some degree of correction of multiplicative variations, although these corrections are somewhat different. Although these two methods make different assumptions about the multiplicative variations in the spectral data, in most practical cases they perform rather similarly when these variations are present in the data. 

Figure 12.16 NIR. diffuse reflectance spectra of 26 poly(urethane) foams, used to demonstrate different classification methods.

Let us consider the tetravalent lanthanide ions first. Because this valency is hard to realize, the number of investigations is restricted. Jorgensen and Rittershaus 3) described the diffuse reflection spectra of Pr + and Tb + in Th02 and Y2O3 and Blasse and co-workers those in Zr02 [4). These spectra show strong absorption bands in the visible which were ascribed to c.t. transitions. 

Fig. 6.12 Diffuse reflectance spectra of hematites of different crystal size (left) and different crystal shape (right) (Hund, 1981, with permission).

Opaque minerals like iron oxides are frequently examined in the reflectance mode - and usually give diffuse reflectance spectra. Reflectance spectra provide information about the scattering and absorption coefficients of the samples and hence their optical properties. The parameters of reflectance spectra may be described in four different ways (1) by the tristimulus values of the CIE system (see 7.3.3) (2) by the Kubelka-Munk theory and (3) by using the derivative of the reflectance or remission function (Kosmas et al., 1984 Malengreau et ak, 1994 1996 Scheinost et al. 1998) and, (4) more precisely, by band fitting (Scheinost et al. 1999). 

The Kubelka-Munk function (f (r)), the remission function, is often used to relate diffuse reflectance spectra to absorption and scattering parameters. This function is the ratio of the absorption, k, and the scattering, s, coefficient and is related to the diffuse reflectance, r, by... 

Figure 7.3-left shows diffuse reflection spectra of the different Fe oxides and Table 7.5 lists their transitions. Fig. 7-3 right summarizes the range of the crystal field band... 

Fig. 7.3 Left Diffuse reflectance spectra of Fe oxides in the UV-Vis-near IR range (Sherman et al., 1982, with permission). Right Median and range of the crystal field band positions determined from second-derivative minima the two...

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