Temperature controlled cell

Coleman and Sivy also used an infrared transmission cell to undertake degradation studies under reduced pressure on a series of poly(acrylonitrile) (ACN) copolymers [30-33]. Thin films prepared from a polymer were mounted in the specially designed temperature-controlled cell mounted within the infrared spectrometer. The comparative studies were made on ACN copolymers containing vinyl acetate [30,32], methacrylic acid [30,31] and acrylamide [30,33]. The species monitored was the production of the cyclised pyridone structure. This was characterised in part by loss of C=N stretch (vC = N) intensity at 2,240 cm-1 accompanied by the appearance and increase in intensity of a doublet at 1,610/1,580 cm-1. 

Fourier Transform Infra Red (FTIR) spectra were obtained using a self supported H+ZSM-5 wafer in an in-situ, atmosphere and temperature controlled cell. The FTIR spectraneter used was a Bomem model DA3. 

Another relevant feature common in the 1950 s was the adaptation of the spectrophotometer in order to permit measurements of temperature-dependent absorbance [7]. The sample was initially immersed in a temperature-controlled water-bath for thermal pre-equilibration. Thereafter, a sample aliquot was selected and placed inside a specially designed temperature-controlled cell where absorbance was measured. In the more sophisticated versions, the instrument was furnished with a peristaltic pump for propelling the sample solution towards the cell and then to waste. 

Spectrophotometry. The analytical reagents were prepared as described by Draganic et al. (5) and the analytical procedure was checked by preparing a set of 0.1, 0.2, and 0.3 mM oxalic-acid complex solutions. The measurements were carried out on a Cary model 15, dualbeam spectrophotometer (Natick) and on a Zeiss PMQII single-beam spectrophotometer (Riso), both with temperature-controlled cell compartments. 

Thermal denaturation studies of DNA and DNA-protein complexes are performed on a UV spectrophotometer equipped with temperature controlled cell holders. Melting of the DNA duplex is indicated by a cooperative hyperchromism at 260 nm. Stabilization by Sac7d is most readily observed with poly[d(AT)]-poly[d(AT)] because of its intrinsic low stability, especially in low salt. The UV melting curve of poly[d(AT)] poly[d(AT)] in 0.01 M K2HPO4 is sharp with a Tm of 43.5° (Fig. 9). In the presence of Sac7d, the melting profile of poly[d(AT)]-poly [d(AT)] broadens and the Tm increases by as much as 33°C for solutions with an excess of Sac7d. The observed Tm for the complex depends on the concentration of protein. 

Temperature controlled IR measurements of liquid samples (solution in CCU) were measured in a Wilmad temperature-controlled cell mount with calcium fluoride windows. The sample was surrounded by a heat sink that was filled with a heat transfer fluid (antifreeze), which was regulated by a Noah Precision temperature controller. The cell mount was sealed in the nitrogen-flushed IR compartment. 

Beer-Lambert s law deviation. For monochromatic radiation, Beer-Lambert s law is always verified and linear in a wide range of solute concentrations. However, experimental deviations occur due to intermolecular interactions (i.e., associations), chemical reaction (e.g., ionization, etc.), or equilibrium displacement due to pH, colloids, or high coloration. Nevertheless, another parameter is the temperature, and for accurate measurements temperature-controlled cells must be used. Finally, the bandwidth of monochromatic radiation is critical in certain region of spectra where slight variations in wavelength lead to large variations in the molar extinction coefficient. 

Fig. 10. UV absorbance measurements were carried out on Beckman UV 5260 UV-VIS spectrophotometer with an electro thermal temperature control cell unit. The temperature control was performed with digital voltmeter with thermocouples. A quartz cell with 1 cm path length was used for all the absorbance studies. Absorbance was measured directly as a temperature function. Thermal unfolding of pepsin was monitored by recording absorbance at 280 nm in temperature interval from 20 °C to 90 °C with heating rate of 1 °C/min and samples were allowed to equilibrate for one minute at each temperature setting, while the reference cell, containing just a solvent, was monitored at room temperature. The resulting increase of the absorbance of the sample solution recorded over the temperature range. Pepsin concentration was 0.3 mg / mUoiution.

There are several ways in which this temperature-sensitivity problem can be minimized. One approach is to put the sample cell in the spectrophotometer and wait until it reaches equilibrium before starting the scan. This can be a time-consuming operation and may be economically impractical. Another is to place the sample cell in the spectrophotometer and scan immediately. The sample must be removed and allowed to return to ambient temperature prior to making the next scan. Filters can be placed ahead of the sample to remove all frequencies but those required for the analysis, so that although the sample will still be heated by the spectrophotometer chassis the rise in its temperature will be much less. Another approach is to build a heat sink or heat-dissipation unit around the sample cell to remove the heat before it can raise the sample temperature. Finally, running the sample in a temperature-controlled cell may be a useful solution. 

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