Signal FTIR spectrometer

One major problem is that of sensitivity (i.e. the signal is very weak owing to the small number of adsorbing molecules). Typically the sampled area is 1cm2 with less than 1015 adsorbed molecules (i.e. about 1 nmol). With modern FTIR spectrometers, however, such small signals (0.01-2% absorption) can still be recorded at relatively high resolution ( 1 cm-1). 

They are especially attractive for analyzing weak light signals. This is because in an FTIR spectrometer all of the frequencies arrive at the detector simultaneously, so that the energy throughput is much greater than for dispersive instruments (the... 

Generally there are two different methods for measuring excited state spectra in the ms time regime. Typically, IR PIA spectra are not recorded with the lock-in technique but by referencing several hundred accumulated single beam spectra (by FTIR spectrometer) under illumination and in the dark, while UV/VIS PIA uses a lock-in detector to filter out signal changes due to photoexcitation. 

Basically, in general PM-IRRAS experiment on any sample with polarized reflectances Rp and Rs, the signal at the detector output can be electronically split into a first part carrying only the intensity modulation induced by the moving mirror of the Fourier transform infrared (FTIR) spectrometer ... 

An interface between gel permeation chromatography (GPC) and Fourier transform infrared (FTIR) spectrometry has been developed. With this system it is possible to collect solvent free polymer deposition and to measure their infrared spectra as a function of molecular weight. The mobile phase from the GPC effluent is converted into an aerosol and removed using a pneumatic nozzle. The sample is collected on a Ge disc that rotates below the nozzle. After the sample is collected, the disc is transferred to an FTIR spectrometer where the infrared spectrum of the sample is collected. Normal GPC sample concentrations (0.1-0.25 wtJvol%) give sufficient sample for useable FTIR signals. All normal GPC solvents can be effectively removed, and the interface works with both low temperature and high temperature GPC applications. 

Figure 26-F1 Instrument diagram for a basic FTIR spectrometer. Radiation of all frequencies from the IR source is reflected into the interferometer where it is modulated by the moving mirror on the left. The modulated radiation is then reflected from the two mirrors on the right through the sample in the compartment at the bottom. After passing through the sample, the radiation falls on the detector. A data acquisition system attached to the detector records the signal and stores it in the memory of a computer as an interferogram. (Courtesy of Thermo Electron Corp., Madison, WI. With permission).

For an FTIR spectrometer, all of the spectral elements are observed for time T. Thus, the time spent sampling the resolution Av is also equal to T. Since the signal-to-noise ratio improves as the square root of the observation time... 

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