Purging/drying, spectrometer

Apparatus Use a Fourier transform infrared spectrometer (FTIR), with its associated computer and peripherals, capable of measuring from 4500 to 500 cm-1 and of acquiring data with a resolution of at least 2 cm-1. The optics of the instmment must be sealed and desiccated, or, like the sample chamber, must be under continuous dry air or nitrogen gas purge. The spectrometer is equipped with software capable of multicomponent analysis using the partial least squares method (PLS-1, or equivalent). This software is commercially available as an accessory to the spectrometer or as an external software package. 

If measurements have to be done in the UV region below 240 nm, it is necessary to purge the spectrometer with dry nitrogen gas in order to remove oxygen. Oxygen absorbs at wavelengths shorter than 240 nm and is transformed into ozone. Absorption by oxygen molecules inside the instalment can make measurements... 

Spectra often display spurious bands. Some of these arise from imperfect compensation of atmospheric absorption bands. Even with good compensation, the spectrometer becomes insensitive when scanning regions of strong atmospheric absorption, so that band contours are distorted. It is worthwhile to purge the spectrometer with dry air or nitrogen. 

The sample is allowed to equilibrate for 15 min inside the instrument before scanning is commenced. The spectrometer is continually purged with dry air to avoid interference from water vapour absorption. 400 scans are averaged at a resolution of 4 cm-1. The scanning is complete for each sample in 1 h. 

Figure lib shows the optical apparatus for PM-IRAS with the high-pressure cell and the photoelastic modulator (PEM) (Hinds-PEM-90) located between the vacuum FTIR spectrometer (Bruker IFS66v/S) and the detector (113,171). By the use of recessed windows, the IR path length inside the high-pressure cell is reduced to minimize gas-phase absorption. To avoid interference from atmospheric H2O and CO2, the IR spectrometer and beam path are evacuated, and only the PEM is purged with dry nitrogen. The IR spectrometer produces a parallel beam of about 40 mm diameter, which is focused on the sample by a parabolic mirror (250 mm... 

The FT-IR spectrometer (Bruker Vertex 70) and the MCT (mercury cadmium telluride) detector are moved out of the accelerator room to be protected against radiation (Fig. 4). The infrared beam is guided on a distance of six meters by dried air or Nj-purged gold coated optical conduits and mirrors. The spectra are obtained from 100 scans with a 4 cm" resolution. Under our conditions, 24 seconds are required to record a spectrum. It is thus possible to follow the evolution of the spectra after irradiation by recording spectra every 30 seconds, for example. In all cases, spectra of irradiated samples are recorded with reference to the same sample just before irradiation, which allows detecting the effects of irradiation by measuring its... 

FTIR spectra were obtained with four wavenumber resolution using either a Nicolet 60-SX or a Mattson Cygnus spectrometer. Specimens were cast as thin films on sodium chloride discs, and the solvent was removed under vacuum at 60 C. The spectrometers were purged with dry, carbon dioxide-free, air. To explore the effect of exposure to moisture, selected specimens were left in the laboratory environment at about 25"C and 40% humidity for several days before being re-examined by FTIR spectroscopy. 

Instrumentation. Spectra were acquired with a Nicolet 60SX FTIR spectrometer, continuously purged with dry air and equipped with a liquid-nitrogen-cooled, wideband mercury-cadmium telluride detector. Coaddition of 100 interferometer scans at 8-cm 1 resolution was employed. The location of absorption maxima was confirmed by spectra taken at l-cm 1 resolution. All spectra were converted into Kubelka-Munk units prior to use. Integration of peak areas was accomplished by using software available on the Nicolet 60SX. All peak areas were normalized to the 1870-cm-1 Si-O-Si combination band (15). 

Spectra were acquired with a Nicolet 60SX FTIR spectrometer, continuously purged with dry air and equipped... 

The films of polymer blends used for the measurements of FT-IR were prepared by casting the polymer solution on the surface of a silicon wafer and dried under vacuum condition for 2 days. The film used in this study was thin enough to obey the Lambert-Beer law (<0.6 absorbance units). FT-IR spectra were recorded on a Perkin-Elmer Spectrum 2000 spectrometer using a minimum of 64 co-added scans at a resolution of 4cm-i. Nitrogen was used to purge CO2 and gaseous water in the detector and sample compartments prior to and during the scans. 

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