Flowing attenuated total reflection

Jarute G, Kainz A, SchroU G, Baena JR, Lendl B (2004) On-line determination of the intracellular poly(P-hydroxybutyric acid) content in transformed Escherichia coli and glucose during PHB production using stopped-flow attenuated total reflection FT-IR spectrometry. Anal Chem 76 6353-6358... 

An example of such inline analysis is shown in Fig. 2.1, in which a flow attenuated total reflection (ATR) infrared spectrometer is installed at the exit of the... 

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... 

Fixed pathlength transmission flow-cells for aqueous solution analysis are easily clogged. Attenuated total reflectance (ATR) provides an alternative method for aqueous solution analysis that avoids this problem. Sabo et al. [493] have reported the first application of an ATR flow-cell for both NPLC and RPLC-FUR. In micro-ATR-IR spectroscopy coupled to HPLC, the trapped effluent of the HPLC separation is added dropwise to the ATR crystal, where the chromatographic solvent is evaporated and the sample is enriched relative to the solution [494], Detection limits are not optimal. The ATR flow-cell is clearly inferior to other interfaces. 

These studies led on to the investigation of on-flow FT-IR using attenuated total reflectance flow cells [23], Although it was initially believed that the use of reversed-phase eluents would not be feasible with IR spectroscopy because of the strong interference resulting from the presence of water, the use of D2O... 

In an effort to gain a better understanding of the initial fouling step leading to bacterial attachment and biofilm formation, we have investigated the adsorption of protein and polysaccharides onto thin metallic films and uncoated internal reflection elements from flowing solutions using attenuated total reflectance spectroscopy. The preliminary results will be described in this paper. 

Sabo et al. [35] developed an LC/FTIR interface for both normal and reversed phase chromatography using an attenuated total reflectance cell. The cylindrical internal reflectance flow cell contained in a ZnSe crystal, had a nominal volume of 24 pi and an equivalent transmission cell path length of 4-22 pi over the usable range. On-the-fly spectra of the components from a 100 pi sample of a solution containing 2% of acetophenone and ethyl benzoate and 1% of nitrobenzene gave clearly identifiable spectra. Nevertheless, relative to other LC/FTIR systems this was not a very sensitive device. 

Haupt and co-workers have created a novel flow injection sensor by applying their 2,4-D MIP (see Section 20.2.5.10.) to the surface of ZnSe attenuated total reflectance crystals [50], In this way, binding of the template could be monitored using FT-IR spectroscopy in the 3500-500 cm region. Three bulk MIPs were... 

Infrared, like the UV and visible regions of the spectrum, provides a useful method for detecting solutes in liquid streams. The detector uses the principle of attenuated total reflectance, with a single beam spectrometer being used in conjunction with a tow volume flow cell. The cell is equipped with sodium chloride, calcium fluoride or zinc selenide windows and can be heated to temperatures greater than 100°C. The detector can... 

The key enabler to using FTIR for BWA detection is to develop selective and robust sampling protocols coupled to a miniaturized, portable FTIR unit. To that end, we have developed front-end liquid flow cells which incorporate electric field (E-Field) concentration methods for spores onto the surface of an Attenuated Total Reflection (ATR) IR crystal. IR spectra are presented which show collection and detection results with BG spores in water. The approaches we have developed take advantage of the fact that all spores are negatively charged in neutral pH solutions. Therefore, E-Field concentration of spores directly onto an ATR sampling element enables low level concentration measurements to be possible. 

Fourier Transform Infrared Spectroscopic and Attenuated Total Reflectance Studies of Protein Adsorption in Flowing Systems... 

Various probes are available for introducing the radiation to the sample. Transmission probes can be either of an insertion or flow-through type. Reflectance probes utilise a reflective surface to return the radiation to the detector. Internal reflectance probes employ attenuated total reflectance at a sample surface to obtain an absorption value. 

Borda, M. J., Strongin, D. R., Schoonen, M. A. (2003). A novel vertical attenuated total reflectance photochemical flow-through reaction cell for Fourier transform infrared spectroscopy, Spectrochim. Acta A Vol. 59,1103-1106, 0584-8539. 

The majority of reported mid-IR fibre probes rely on the well-established attenuated total reflection (ATR) technique, revealing many advantages in the general applicability over e.g. absorption measurements in short pathway flow cells. In the ATR method only a thin film (a few micrometers) at the proximity of the ATR element is subject to the measurement The thickness of the analyzed film is defined by the penetration depth of the evanescent field... 

One of the most common uses of IR spectroscopy in the analysis of fatty acids and fats is the determination of fmn -unsaturation. An interesting procedure for tran5-unsaturation using IR attenuated total reflectance (ATR) spectroscopy has been described (Sipos and Ackman, 1978). The samples do not have to be weighed or diluted. A special ATR cell is used to make readings at 10.3 / m. The system can be used to monitor a continuous flow system, and the presence of catalyst does not affect the readings. 

Three types of flow cells can be discerned for online LC-FTIR coupling, and these are respectively based on transmission, attenuated-total-reflection (ATR), or specular reflection measurements. The spectral range (i.e., detection wave number range) of these interfaces is determined by the IR characteristics of the applied cell-window material and by the mobile phase used for the chromatographic separation. 

A less technically complicated approach for tracking the surface dehydration ability of proteins and polymers is by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Accordingly, a solution of a surface binding solute is pumped into a flow cell with a Zn-Se crystal sensor, where it is irradiated with IR light and reflected to a detector. The surface chemistry and area of the sensor are specified and the surface area increased using different types of nanobeads (50 nm in diameter). 

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