Infrared reference beam

There is supporting evidence in the literature for the validity of this method two cases in particular substantiate it. In one, tests were made on plastics heated in the pressure of air. Differential infrared spectroscopy was used to determine the chemical changes at three temperatures, in the functional groups of a TP acrylonitrile, and a variety of TS phenolic plastics. The technique uses a film of un-aged plastic in the reference beam and the aged sample in the sample beam. Thus, the difference between the reference and the aged sample is a measure of the chemical changes. 

The light from the infrared source C is made to split into two beams one of which passes through the sample i.e., the sample beam) while the other caters as the reference beam. This sort of double-beam arrangement facilitates in measuring difference in intensities between the two beams at each wavelength,... 

Infrared spectra were recorded on the resist film spun onto a silicon wafer using a JASCO IR-810 spectrometer equipped with a JASCO BC-3 beam condenser or a JASCO A-3 spectrometer. In the measurements on the latter spectrometer an uncoated silicon wafer was placed in the reference beam in order to balance the silicon absorption band. The subtraction between the spectra was carried out on a built-in micro-processor attached to the IR-810 spectrometer, and the resulting difference spectrum was used to detect structural changes in the polymer molecule upon exposure. The subtraction technique was also used to balance the silicon absorption band. 

For IR measurements the catalyst was compressed at 4 X 108 Pascal. The disc (18 mm diameter, 20-30 mg) was mounted in a quartz sample holder which was introduced in the adsorption/infrared cell (10). To avoid the reduction of the Pd(II) ions by hydrocarbons, the cell was grease free. Samples were activated according to treatment c. Spectra were recorded on a Perkin Elmer model 125 grating spectrometer. The reference beam was attenuated, and the instrument was flushed with air freed of H20 and C02. 

Carbon monoxide was introduced at 25° C under an equilibrium pressure around 50 torr. Infrared spectra were recorded on a Perkin-Elmer grating spectrophotometer model 125. The reference beam was attenuated, and the instrument was continuously flushed with air freed from C02 and water. 

A gas-washing bottle (Figure 4.7B) may also be used for trapping. This technique is especially useful in conjunction with infrared analysis. The sample is simply bubbled through the anhydrous solvent as it exits the chromatographic column. The solution is then placed in a liquid sample infrared cell. A matching cell containing only the solvent is placed in the reference beam. An infrared spectrum of the sample may then be recorded. 

In the pressed disc technique a known weight of sample is intimately ground with pure, dry potassium bromide and the mixture inserted into a special die and subjected to pressure under vacuum. The concentration of sample in the disc is usually in the region of 1.0 per cent. The disc so produced may be mounted directly in the sample beam path of the spectrophotometer and the spectrum recorded. This method has the advantage that the spectrum so produced is entirely due to the sample since pure dry potassium bromide is infrared transparent in the 2-25 /xm region. To eliminate the possibility of impurities in the potassium bromide, however, a blank disc (no sample) can be made and mounted in the reference beam path of the spectrophotometer. Care should be taken to ensure that both discs are of equal thickness otherwise inverse peaks may occur if the potassium bromide is damp or impure, and this will be particularly noticeable if the reference disc is thicker than the sample disc. 

Spectrophotometry. Infrared spectra were obtained with a Perkin Elmer Model 281B Spectrophotometer interfaced with a computer data station. Films were encased in sample holders in the reference beam, and spectra were obtained with air as reference. The spectra were scanned from 1900 - 1500 cm-l at a scanning time of 60 minutes with a response setting of 2. The slit program was set at N. All spectra were recorded on computer disks. 

A Mutiple Internal Reflection Accessory for use with Perkin-Elmer infrared spectrophotometers was used to introduce the sample to the IR beam. To correct for losses in energy transmittance through the sample beam resulting from the use of the MIR Accessory, a comb-type reference beam attenuator was employed. A LFE Corpora-... 

For infrared analysis, each standard quartz filter or redeposited sample filter is cut in half with surgical scissors and placed on the 30 or desired angle setting of the MIR ccessory base. The IR is adjusted to a scan setting of 750 cm and the reference beam attenuator is used to bring the transmittance level to 90-l(j)0%. The filter is then scanned in duplicate from 900 to 700 cm. pie spectrum is recorded yn absorbance chart paper. 

The infrared spectrum of the precipitated polystyrene at this stage exhibited no absorption using thermally polymerized polystyrene in the reference beam. A 3.5% solution of dried Triton X-405 in chloroform showed intense adsorption at about 1100 cm. 1, characteristic of the ether linkage. 

An infrared spectrometer measures the frequencies of infrared light absorbed by a compound. In a simple infrared spectrometer (Figure 12-4), two beams of light are used. The sample beam passes through the sample cell, while the reference beam passes through a reference cell that contains only the solvent. A rotating mirror alternately allows light from each of the two beams to enter the monochromator. 

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