FTIR sampling techniques

With respect to the practical part of this chapter a short excursion into the theory and application of FTIR sampling techniques is recommended. More details concerning the sampling techniques are found in special literature (Chalmers and Griffiths, 2002 Giinzler and Heise, 2003 Karge and Geidel, 2(X)4 Zaera, 2012). 

FTIR is particularly useful in the study of composite materials yielding much information about the molecular structure of coupling agents on various substrates, including silica, metals and fillers. Ishida et al. [86] used a non-destructive FTIR sampling technique to study glass fibre composite interfaces. 

Lastly, ATR is probably the most expensive FTIR sampling technique available. Very basic accessories cost several thousand dollars, and diamond ATRs cost even more. That being said, the time saved in sample preparation often pays for the ATR accessory. Table 4.13 lists the advantages and disadvantages of the ATR sample preparation technique. 

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. 

The combination of FTIR spectroscopy and the CIRCLE cell sampling technique proved useful in the investigation of the hydrolysis and condensation... 

Majority of the sampling techniques described in the literature involve the direct analysis of pieces of cheese, with the primary aim of simplifying the procedure and reducing the analysis time. Our research group has believed that in order to fully tap the potential of FTIR spectroscopy, minimize interferences from the cheese matrix, and successfully analyze minor compounds, a simple extraction procedure may be required. Several extraction methods were discussed earlier in this chapter. However, none of them were adopted for the FT-MIR analysis of cheese until Koca et ah (2007) analyzed the WSE of Swiss cheese to determine short-chain fatty acids. A comparison of the analysis of WSE with the direct analysis of... 

The introduction of Fourier Transform Infrared Spectroscopy (FTIR) brought along a number of typical solid sample techniques. DRIFTS (Diffuse Reflectance Fourier Transform Infrared Spectroscopy) is probably most commonly known. Another technique, developed specifically for measuring solid, opaque samples is PAS (Photo Acoustic Spectroscopy). This accessory is less known, probably due to its high cost and its rather difficult modus operandi. 

Infrared spectroscopy (IR) is one of the oldest instrumental analytical techniques but its value in structural analysis has decreased with the rise of nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). Compared to the traditional dispersive IR techniques, Fourier transform infrared spectroscopy (FTIR) offers more sampling techniques. 

One challenge in the analysis of the CWA is the analysis of their precursors and degradation products, which are often nonvolatile. The CWA degrade, for example, hydrolyze or oxidize easily. Traditional IR sampling techniques, like KBr pellets and liquid cells are well suited for analysis of neat or concentrated nonvolatile chemicals. Environmental samples containing these kind of chemicals, however, normally require derivatization before GC/FTIR analysis. 

Two problems should be considered when conducting an investigation that incorporates mapping and sampling techniques. One problem is that the irreplaceable and fragile nature of the textile evidence demands nondestructive or minimally destructive procedures. Removal of enough microsized samples to provide a statistical sample would destroy much of the textile. Another consideration is that the cost of techniques such as as X-ray diffraction (XRD) or Fourier transform infrared spectroscopy (FTIR) would be prohibitive when applied to a large number of samples. Because of these constraints, chemical and physical data should be obtained from a limited number of locations. These areas can best be identified once a survey of the evidence has been conducted and technical fabrication analyses of evidence obtained from a random sample of locations have been performed. 

With the continuous improvement of sampling techniques, software, and instrumental designs, more and moresophisticated FTIR spectrometers are now available. Analytical Chemistry biannually reviews the most recent developments in many fields of analytical techniques, including infrared spectroscopy, many times on a yearly basis. 

Hyphenated techniques refer to the combination of one or more analytical techniques for problem solving and fundamental research. Numerous types have been reported in the scientific journals. Frequently the FTIR spectrometer is coupled with chromatographic instruments for the structural characterization of a column eluent. These systems are designed to monitor the eluent or to obtain its spectrum. Much of the development has been focused on the sampling technique and the design of the interface between the chromatographic system and the FTIR spectrometer to improve the performance of the system. 

Fourier transform infrared microscopy is the primary infrared technique for structural identification of materials at microquantities. The method is non-destructive and non-invasive. When using a proper transmittance sampling technique and a proper detector, the limit of detection can be as low as the picogram level. In the pharmaceutical industry, FTIR microscopy is used to analyze bulk drugs, excipients, and particulate contaminants. " Recent studies have shown that by coupling FTIR microscopy with GC, HPLC, SFC, or GPC systems, the detection limit of the method is substantially improved. ... 

The primary reason FTIR has not been utilized as a point detection system for trace level contamination in water is that the opacity of water limits the pathlength (L) to 25 pm or less. Based on a minimum CL value of 0.22 pg/cm for phosmet, the minimum detection level would be approximately 10 ppm. Therefore direct detection at low ppb levels in the aqueous phase is not possible. The avenue to achieve a lower detection limit is to increase the concentration (C) in the IR beam. The work presented in this paper has focused on synthesizing and modifying adsorbent materials that would serve as the above mentioned concentrating surface. The main hmdle is to incorporate these adsorbent materials into a sampling technique that will allow trace detection from aqueous systems, while utilizing the inherent selectivity of FTIR spectroscopy. 

The introduction of in-situ infrared spectroscopy to electrochemistry has revolutionised the study of metal/electrolyte interfaces. Modnlation or sampling techniques are applied in order to enhance sensitivity and to separate snrface species from volume species. Methods such as EMIRS (electrochemicaUy modulated IR spectroscopy) and SNIFTIRS (subtractively normalised interfacial Fonrier Transform infrared spectroscopy) have been employed to study electrocatalytic electrodes, for example. There have been surprisingly few studies of the semiconductor/electrolyte interface by infrared spectroscopy. This because up to now little emphasis has been placed on the molecnlar electrochemistry of electrode reactions at semiconductors because the description of charge transfer at semiconductor/electrolyte interfaces is derived from solid-state physics. However, the evident need to identify the chemical identity of snrface species should lead to an increase in the application of in-situ FTIR. 

This chapter will focus on the appHcation of FTIR spectroscopy in the quantitative analysis of foods. Following a brief discussion of the fundamental principles of IR spectroscopy, we wiU describe the instrumentation, data handling techniques, and quantitative analysis methods employed in FTIR spectroscopy. We will then consider the IR sampling techniques that are most useful in FTIR analysis of foods. Finally, a survey of FTIR applications to the quantitative analysis of food will be presented. Although important, the so-called hyphenated techniques, such as GC-FTIR, will not be covered in this chapter. Similarly, near-IR (NIR) spectroscopy, which has found extensive use in food analysis, is beyond the scope of this chapter. 

Investigations of the acidity of specific surface sites may be accomplished by studies coordinated with spectroscopic methods, such as infrared (JR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, or mass spectrometry (MS). Surface characterization with Fourier transform infrared (FTIR) spectroscopy can provide quantitative results with experimental methods that are easily performed. However, the transmission sampling techniques traditionally employed for infrared studies may introduce experimental artifacts on the analyzed surface (10,... 

IR spectroscopy is one of the few analytical techniques that can be used for the characterization of solid, liquid, and gas samples. The choice of sampling technique depends upon the goal of the analysis, qualitative identification or quantitative measurement of specific analytes, upon the sample size available, and upon sample composition. Water content of the sample is a major concern, since the most common IR-transparent materials are soluble in water. Samples in different phases must be treated differently. Sampling techniques are available for transmission (absorption) measurements and, since the advent of FTIR, for several types of reflectance (reflection) measurements. The common reflectance measurements are attenuated total reflectance (ATR), diffuse reflectance or diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and specular reflectance. The term reflection may be used in place of reflectance and may be more accurate specular reflection is actually what occurs in that measurement, for example. However, the term reflectance is widely used in the literature and will be used here. 

These are the oldest and most basic sampling techniques for IR spectroscopy and apply to both FTIR and dispersive IR systems. Transmission analysis can handle a wide range of sample types and can provide both qualitative and quantitative measurements. Transmission analysis provides maximum sensitivity and high sample throughput at relatively low cost. There is in some cases substantial sample preparation required. 

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