Attenuated total reflectance accessory

Figure 1 Attenuated Total Reflection accessory for FTIR spectrometer with diamond crystal through which infrared beam is reflected (upper). Plastic samples must have good contact with the surface of the diamond to obtain well-resolved spectra (lower)...

Infrared Spectroscopy. Fourier transform Infrared spectroscopy (Perkln-Elmer 1750) was used to measure surface characteristics of samples of various percent conversion. An attenuated total reflectance accessory with KRS-5 crystal (45°) provided sufficient absorp-... 

Attenuated Total Reflection accessory for FTIR spectrometer with a diamond crystal in the centre through which the infrared beam is reflected. 

Fourier Transfer Infrared (FTIR) spectra of lignin were acquired on a Thermo Nicolet Nexus 470 FTIR spectrometer with a Golden Gate Heatable Diamond ATR (attenuated total reflectance) accessory at room temperature. The number of scans for each sample was 32. The assignments of absorbance peaks were based on published FTIR database for lignin (77). 

Preparation of solid samples for analysis by infrared analysis has tended to be much more labor intensive than analysis of liquids. The traditional methods involve preparation of a KBr pellet or a Nujol mull described in sections 25.5 B and 25.5 C. The use of an attenuated total reflectance accessory with an FT-IR instrument has dramatically improved the preparation time previously required. One simply places a small amount of a solid on the instrument. For these laboratories equipped with this accessory, it is strongly recommended for analysis of both solids and liquids (Section 25.1). 

Chan KLA, Tay FH, Poulter G, Kazarian SG. Chemical imaging with variable angles of incidence using a diamond attenuated total reflection accessory. Appl Spectrosc 2008 62 1102-1107. 

Figure 2.8 Attenuated total reflection accessory containing a multireflection single-pass element.

The experimental apparatus consists of a gas flow system with a four-port valve, a multi-reflection Attenuated Total Reflection (ATR) accessory (Pike Technologies), and a custom reactor manifold mounted to the ATR top plate, shown in Fig. 45.1. The ATR reactor manifold consists of (i) a Cap2 window for UV irradiation, (ii) an inlet and outlet port, and (iii) an injection port for the liquid phase reactant. 

FTIR instrumentation is mature. A typical routine mid-IR spectrometer has KBr optics, best resolution of around 1cm-1, and a room temperature DTGS detector. Noise levels below 0.1 % T peak-to-peak can be achieved in a few seconds. The sample compartment will accommodate a variety of sampling accessories such as those for ATR (attenuated total reflection) and diffuse reflection. At present, IR spectra can be obtained with fast and very fast FTIR interferometers with microscopes, in reflection and microreflection, in diffusion, at very low or very high temperatures, in dilute solutions, etc. Hyphenated IR techniques such as PyFTIR, TG-FTIR, GC-FTIR, HPLC-FTIR and SEC-FTIR (Chapter 7) can simplify many problems and streamline the selection process by doing multiple analyses with one sampling. Solvent absorbance limits flow-through IR spectroscopy cells so as to make them impractical for polymer analysis. Advanced FTIR... 

The infrared technique has been described in numerous publications and recent reviews were published by Davies and Giangiacomo (2000), Ismail et al. (1997) and Wetzel (1998). Very few applications have been described for analysis of additives in food products. One interesting application is for controlling vitamin concentrations in vitamin premixes used for fortification of food products by attenuated total reflectance (ATR) accessory with Fourier transform infrared (FTIR) (Wojciechowski et al., 1998). Four vitamins were analysed - Bi (thiamin), B2 (riboflavin), B6 (vitamin B6 compounds) and Niacin (nicotinic acid) - in about 10 minutes. The partial least squares technique was used for calibration of the equipment. The precision of measurements was in the range 4-8%, similar to those obtained for the four vitamins by the reference HPLC method. 

IR spectra of starch can be obtained with an IR spectrometer such as a Digilab FTS 7000 spectrometer, Digilab USA, Randolph, MA, equipped with a thermoelectrically cooled deuterated tri-glycine sulfate (DTGS) detector using an attenuated total reflectance (ATR) accessory at a resolution of 4 cm by 128 scans. Spectra are baseline-corrected, and then deconvoluted between wavenumbers 1200 to 800 cm . A half-band width of 15 cm and a resolution enhancement factor of 1.5 with Bessel apodization are employed. Intensity measurements are performed on the deconvoluted spectra by recording the height of the absorbance bands from the baseline. 

The mechanical simplicity of an FTIR spectrometer contrasts sharply with its theoretical complexity. The only moving part is the mirror, which rides on air or mechanical bearings to facilitate maintenance and improve reliability. The round cross-section of the FTIR beam is especially advantageous in situations where a circular attenuated total reflectance (CATR) accessory for liquids is used. For heat-sensitive compounds it is important to note that the sample is not heated significantly during the FTIR measurement. 

A method of horizontal attenuated total reflectance (HATR) by Fourier transform infrared spectroscopy (FTIR) is considered more useful for infrared spectroscopic analysis of leather samples. By this method, the sample is simply put on the flat plate of ZnSe crystal or KRS-5 crystal of the HATR accessory. The Fourier transformation of the interferogram is converted by the computer into a plot of absorption against wave number that resembles the usual IR spectrum (William and Fleming, 1998). 

Specialised sampling techniques such as attenuated total reflectance (ATR) and diffuse reflectance (DR) have been found to be exhemely effective and hence have gained considerable popularity. Microsampling, for measuring very small samples, has become a common technique over the last decade as beam condensers and infrared microscopes (plus accessories) have been improved. 

Figure 12 Schematic representation of an infrared transmission cell (top) and of an attenuated total reflectance (ATR) accessory (bottom).

Double beam spectrophotometers allow differential measurements to be made between the sample and the analytical blank. They are preferable to the single beam instruments for cloudy solutions. The bandwidth of high performance instruments can be as small as 0.01 nm. For routine measurements such as monitoring a compound on a production line, an immersion probe is employed. Placed in the sample compartment of the apparatus this accessory contains two fibre-optics, one to conduct the light to the sample and another to recover it after absorption in the media studied. Two types exist by transmission for clear solutions and by attenuated total reflection (ATR) for very absorbent solutions (Figure 9.17). 

The most widely available technique for identifying mainly polymer, but also additives in plastics, is Fourier Transform Infrared (FTIR) spectroscopy. Samples are exposed to infrared light (4000-400 wavelengths per centimetre or cm ) causing chemical bonds to vibrate at specific frequencies, corresponding to particular energies. In the last 5 years, an accessory for FTIR has been developed, which enables non-destructive examination of surfaces and so is ideal for analysis of plastics in museum collections. Attenuated Total Reflection-FTIR (ATR-FTIR) requires samples to be placed on a diamond crystal with a diameter of 2 mm through which the infrared beam is reflected... 

Attenuated total reflectance (ATR) accessories are especially useful for obtaining IR spectra of samples that cannot be readily examined by common transmission methods. Such accessories are suitable for studying thick or highly absorbing solid and liquid samples, including films, coatings, powders, threads, adhesives, polymers, and aqueous samples. ATR requires only little sample preparation for most samples, it is one of the most versatile sampling techniques. 

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) data were obtained from the surfaces of modified PU sheets using a Mattson Alpha Ceiitauri FTIR spectrophotometer, coupled with an ATR accessory and 45 ° KRS-5 crystal. 

Fig. 1. Schematic diagram of the attenuated total reflection of the infrared beam in a monoreflection ATR accessory.

Infrared microspectroscopy has been applied to the study of macerals (organic fractions) from a wide range of coals [106,116] and oxidized coal [117]. It may be performed either in transmission or reflection [106]. In the former case, sample preparation is tedious, and transmission IR microspectroscopy is seldom used. The preparation of samples for reflection measurements is simpler for example, the technique of attenuated total reflectance (ATR) has been applied to the study of coal [106]. Indeed, if the standard ATR accessories (which have been available for many years) were not suitable for block coal samples, recently, an ATR lens, equipped with a silicon (or germanium) internal reflection element, has become available for use with IR microscopes, and the technique was successfully applied... 

ATP Accessory. Modern FT-IR instruments now offer an attenuated total reflectance (ATR) accessory along with the typical transmittance module. The ATR method provides a powerful sampling technique that virtually eliminates sample preparation with both liquids and solids, thus leading to a dramatic improvement in throughput in the teaching laboratory. Although manufacturers offer multiple crystal options, the diamond ATR offers the best option for maximum durability in... 

There are several options for preparing a solid sample for IR spectroscopy. These include the preparation of solutions, castings, KBr pellets, and microporous polyethylene films, or the use of an accessory for obtaining attenuated total reflectance... 

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