ATR-FTIR difference spectra

Figure 1. ATR-FTIR difference spectra of a) aqueous bicarbonate and b) carbonate ions from solutions of 1.0 M NajCOj at pH 11.2 and 7.9, respectively. Subtracted spectra were of NaCl at the same concentration and pH. Spectra taken from Su and Suarez (75).

Fig. 1 ATR-FTIR absorbance spectra after different treatment steps of PP foils using a Ge crystal and 45° angle of incidence...

The ATR technique is a commonly used infrared internal reflection sampling technique. It samples only the surface layer in contact with the ATR element the sampling depth probed is typically of the order of 0.3-3 pm [1]. Unless software corrected, compared with a transmission spectrum, the relative intensity of bands within an ATR spectrum increase in intensity with decreasing wavenumber. Several FTIR instrument companies now supply "ATR-correction" software developed to correct for the different relative intensities of bands observed between ATR and transmission spectra, so that ATR spectra can be more easily compared to and searched against transmission spectra. 

Figure 69 shows the ATR-FTIR spectra of the inside heat seal layer of the white film from both the "good" and "bad" packages. A library spectrum of an EVA copolymer is also shown for comparison. The heat seal layer is identified as EVA, based on the position of peaks in the sample spectra compared to the library EVA spectrum. The heat seal layer appears to have a lower vinyl acetate content compared to the library spectrum, which was acquired from a 14% vinyl acetate copolymer. There were no significant spectral differences between the spectra of the "good" and "bad" samples. 

The RAIR and ATR spectra were obtained using a Perkin-Elmer Model 1800 FTIR equipped with Harrick Scientific Co. external reflection and internal reflection accessories. Reflection spectra of the aluminum side of the fracture surfaces were referenced to spectra obtained from freshly polished aluminum substrates to obtain difference spectra of material left on these surfaces. 

Figure 3.10 (a) ATR-FTIR spectra of mix EOZ4 (after 1 h moulding) (b) ATR-FTIR spectra of mix EOZ4 (after 1 min moulding) (c) Difference spectrum (a-b)... 

In order to get a fast characterization of the degradation processes, the individual semiconductors (MDMO PPV and Ceo) and a blend of the two semiconductors as used in bulk heterojunction solar cells are studied under illumination in pure oxygen. ATR-FTIR spectra before and after an 8 h degradation process and difference spectra showing only the spectral changes... 

Due to the significant difference in the mid-infrared spectra of proteins and polysaccharides, it is possible to study simultaneously and independently their behaviours in mixtures.6 In this study ATR-FTIR was used to monitor starch gelatinisation and the evolution of the water content dependent hydrogen bonding in the gluten fraction of starch/gluten mixtures as a function of heating. 

Figure 7. ATR FTIR spectra of the styrene acrylic acid copolymer in the 2200-1000-cm region. A is the aqueous solvent spectrum. B through E are the difference spectra of various concentrations of styrene acrylic acid minus solvent. Reproduced with permission from ref. 19. Copyright 1987 Applied...

The Raman effect is very small and until recently its use as an analytical tool was limited by a lack of suitable equipment. Recent advances, particularly the development of higher resolution and lower cost systems, mean that Raman spectroscopy is now used to analyse a wide range of materials. Raman spectroscopy is totally non-destructive although dark samples may become very hot and bum. Using a microscope, spectra can be recorded from very small samples, as small as 1-2 pm across, and from the different layers present within a laminate. Whereas ATR-FTIR gives information from a depth up to around 2 pm into the material, Raman spectroscopy has a penetration depth in the order of millimetres. 

Molybdenum. Sorption of Mo onto am-Fe(OH)3 was examined by Goldberg et al. (27) using FTIR. The Mo04 aqueous species is dominant in most natural systems (pK j for molybdic acid = 4.2). The ATR-FTIR spectrum for Mo04 reported by them showed peaks at 933, 885, and 835 cm in reasonable agreement with the earlier published vibrational spectra (Table I). The Mo, am-Fe(OH)3 ATR difference spectrum showed peaks at 928 and 880 cm similar to aqueous Mo04 thus adsorbed Mo was not detected. 

The position of the v(C=N) bands differs depending on the different substituents at the nitrogen atom of the N-benzylidene ring. Typical modes of the aromatic rings appear around 1595/1575cm as well as 1495/1485/1458cm. The respective ATR-FTIR and Raman spectra of the hydrogenation products show less prominent bands with essentially lower intensities ]11]. 

In one method, by varying the thickness of a barrier film, different effective penetration depths are achieved (194). ATR-FTIR spectra of a laminate (PMMA/PVAL) were presented at different base layer thicknesses and different angles of incidence on a zinc selenide substrate. By varying the thickness of the PMMA barrier film, different effective penetration depths in the PVAL were achieved to detect interfacial interactions (245). 

FIGURE 5.15 The ATR-FTIR spectra of the unmodified membrane (NFPESIO) and the modified membranes with 30 g/1 NVP at 5 min UV-irradiation time (30NVP-5). (From Desalination, 287, Abu Seman, M.N., Khayet, M., and Hilal, N., Comparison of two different UV-grafted nanofiltration membranes prepared for reduction of humic acid fouling using acrylic acid and N-vinylpyrrolidone, 19-29, Copyright (2012), with permission from Elsevier.)... 

Site-specific interactions between the —NO2 groups of sorbed NAC molecules in the interlamellar region of smectites and exchangeable cations were first proposed to account for NAC sorption by Yariv and coworkers over 30 years ago (72,73). They found that the vibrational bands of the sorbed NACs were shifted relative to the neat compound. The spectral trends in this study were not conclusively related to the nature of the exchangeable cation because of differences in water content (73). More recently, evidence against site-specific interactions was reported by Weissmahr and coworkers based on spectral similarities between NACs sorbed on K - and Cs +-exchanged clays obtained using UV-visible, infrared, and NMR methods (6). They reported spectral shifts in the ATR-FTIR spectra of sorbed NACs relative to the NAC in aqueous solution. However,... 

---