Cylindrical internal reflectance cell

The rate for the Ir reaction was measured at temperatures up to 120 °C and CO pressures up to 6 bar in PhCl by IR using a cylindrical internal reflectance cell... 

An infrared spectrum is a plot of percent radiation absorbed versus the frequency of the incident radiation given in wavenumbers (cm ) or in wave length ( xm). A variation of this method, diffuse reflectance spectroscopy, is used for samples with poor transmittance, e.g. cubic hematite crystals. Increased resolution and sensitivity as well as more rapid collection of data is provided by Fourier-transform-IR (FTIR), which averages a large number of spectra. Another IR technique makes use of attenuated total reflectance FTIR (ATR-FTIR) often using a cylindrical internal reflectance cell (CIR) (e.g. Tejedor-Tejedor Anderson, 1986). ATR enables wet systems and adsorbing species to be studied in situ. 

ATR studies of the biocorrosion of submerged copper surfaces have been reported. The IRE of a cylindrical internal reflectance cell (CIRCLE) was coated with a thin copper layer via a vacuum deposition technique (105). The copper layer reduces the sampling depth of the radiation outward from the surface of the IRE. Therefore, the intensity of the water bending band will vary with copper layer thicknesses of 4.1 nm or less. The copper layers were shown to be stable to exposure to water alone, but the presence of acidic polysaccahrides in the water caused a reduction in the copper layer thicknesses (106.107). The adsorption of a model compound, Gum Arabic, onto the coated IRE was detected by increases in the C-O stretching band of the pyranose units near 1050 cm"1 (106). 

The use of cylindrical internal reflectance cells for HP-IR was pioneered by Moser and further modified by others.This method involves the use of an optically transparent internal reflectance crystal (typically ZnS, ZnSe, sapphire). Due to the inherently short path length, the method is not as sensitive as transmission-based IR, and a Fourier transform infrared (FTIR) spectrometer is therefore generally required. In addition, the type of crystal may need to be changed depending on the reaction of interest, as the optics may be corroded by some reagents or catalysts. However, as the path length is fixed regardless of conditions, it is much easier to quantify catalyst species, and unlike transmission systems the cells can also be used for the study of liquid-solid and gas-liquid-solid mixtures. ... 

The ATR technique is now routinely used for IR spectroscopy as it allows measurement of spectra for a variety of sample types with minimal preparation. The crystals employed are generally prismatic in shape, allowing contact of a flat surface with the sample. The ATR method was first adapted for HP IR spectroscopy by Moser [29-33], who realised that a conventional autoclave could easily be adapted for in situ IR spectroscopy by fitting an ATR crystal of cylindrical cross section. The technique developed by Moser is thus known as cylindrical internal reflectance (CIR) spectroscopy and high pressure cells based upon the CIR method have been commercialised by Spectra-Tech. A typical CIR cell is illustrated in Figure 3.8. 

Historically, high-pressure IR spectroscopy has been one of the most important methods to measure intermediates or resting-state species in catalytic cycles. In 1%8, Wilkinson observed HRh(PPh3)2(CO)2 in the Rh/PPh3 catalyst system by IR spectroscopy where an IR cell was connected via a tube to the autoclave. A related study was performed more recently by Moser et who applied their cylindrical internal reflectance IR cell. They determined the rate-... 

Using a cylindrical internal reflectance (CIRcle) cell and GC-IR data collection software, it was determined for both lysozyme and BPN, that most of the enzyme adsorption occurred within ten seconds after injection. Nearly an order-of-magnitude more BPN adsorbed on the hydrophobic surface than the hydrophilic one, while lysozyme adsorbed somewhat more strongly to the hydrophilic Ge surface. Over time periods of about one day, the lysozyme layer continued to increase somewhat in thickness, while BPN maintained its initial coverage. 

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. 

The techniques of Cylindrical Internal Reflectance (CIR) and Diffuse Reflectance spectroscopies are described herein. The CIR phenomenon was employed in three different apparatus. Two different high pressure CIR cells were used to study reactions homogeneously catalyzed by [y-HW2(CO)10]-. Low temperature reactions of Mo and W complexes were studied using an ambient pressure CIR cell. The diffuse reflectance technique was employed to study powdered samples of Ru carbonyl complexes supported on A1203. 

The combination of these two powerful characterisation techniques can provide the ability simultaneously to characterise the molecular distribution and to identify and quantify IR-active functional groups in the distribution. The main problem in linking such technologies is the choice of solvent or eluent used to carry the polymer through the SEC system. Many of the typical SEC solvents have strong absorption bands in wide regions of the infrared spectrum. Developments have centred around the use of low-volume cylindrical internal-reflection flow cells for use in the FTIR system. However, their use is still restricted in many cases to IR-friendly SEC solvents. 

ATR accessories for the measurement of liquids are not restricted to IREs with a trapezoidal or parallelpiped geometry. Alternatively, liquids can be measured with cylindrical IREs. A cylindrical internal reflection element is a rod that has a cone at each end, as shown in Figure 15.10. The cone typically has a 45° half-angle at the apex. The IRE is sealed into a liquid cell that exposes most of the rod to the liquid, and only the ends of the cell extend beyond the cell. Two geometries for cylindrical IREs are shown in Figure 15.11. The first (Figme 15.11a) is the CIRCLE cell (Thermo Spectroscopy Division, Madison, Wisconsin), where CIRCLE is an... 

---