FTIR Hardware

So far we have discussed how the parts of an FTIR work together to measure an interferogram and ultimately obtain a spectrum. It is now time to look at how each of these pieces works by themselves. 

FIGURE 2.23 An illustration of how the moving mirror of a Michelson interferometer can be translated back and forth by use of a shaft attached to a motor. Note that the mirror housing is stationary, and that friction occurs between it and the shaft. 

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Overall, most of the requirements for a process spectrometer/analyzer are straightforward to implement, but they do require attention at the design level. Another important area, which is FTIR specific, is the user interface and the need to provide for industry standard data communications. Standard software packages do exist for process instrumentation. For prototype development, and even for the front-end interface in a stand-alone mode of operation, software products, such as National Instraments Lab View and the Mathworks MatLab, are also important instrumentation development tools. Note that National Instruments also provides important computer-based electronics and hardware that meet most of the computer interfacing, and system control and communications needs for modem instrumentation. For practical installations, a product known... 

The contents of the book are intended to help a newcomer in the field, as well as to provide current information including developing technologies, for those who have practiced process analytical chemistry and PAT for some time. The main spectroscopic tools used for PAT are presented NIR, Raman, UV-Vis and FTIR, including not just the hardware, but many apphcation examples, and implementation issues. As chemometrics is central for use of many of these tools, a comprehensive chapter on this, now revised to more specifically address some issues relevant to PAT is included. In this second edition many of the previous chapters have been updated and revised, and additional chapters covering the important topic of sampling, and the additional techniques of NMR, fluorescence, and acoustic chemometrics are included. 

No special hardware or software is required for either the chromatograph or the FTIR. Interface to the chromatograph is accomplished by diverting the sample-solvent flow from the end of the GPC column to the nozzle assembly via a flow divider. The flow divider allows the selection of a portion of the flow from the chromatograph to the nozzle. The quantity of flow depends on the viscosity of the mobile phase and the nature of the polymer being analyzed. The nozzle can evaporate up to 150 /iL/min THF and TCB. The nozzle design is shown in Figure 1. 

The DRIFTS studies were carried out at different temperatures on a Nicolet 20 SXB FTIR spectrometer equipped with a commercial DRIFTS catalytic chamber and associated hardware from Spectratech . The DRIFTS cell is a temperature-controlled flow-through reactor. Upon calcination, samples were cooled to room temperature under nitrogen. Subsequently, 25 microliters (liq.) of the chosen alcohol were injected and spectra were collected at 373, 473, 623 and 773 K during the heating cycle. A spectral resolution of 4 cm was used. 

Fundamentally, EGA systems require powerful software control and data analysis systems, which, in addition to overall hardware control and displaying and analyzing output data, may also store reference libraries of MS or FTIR spectra to assist identification of the gaseous products of a thermal decomposition. However, EGA represents the most comprehensive group of thermoanalytical systems available for the characterization of the thermal behavior of materials. 

TGA is used to determine the loss in mass t particular temperatures, but TGA cannot identify the species responsible. To obtain this type of information, the output of a thermogravimetric analyzer is often connected to a Fourier transform infrared (FTIR) or a mass spec-Irometer(MS). Several instrument companies offer devices to interface the TGA unit toa spectrometer. Some even claim true integration of the software and hardware of the TGA/MS or TGA /FTIR systems. High-Resolution TGA... 

As we have seen, the availability of software and hardware to do molecular mechanics, quantum chemistry, and molecular dynamics is not the problem. How to incorporate this software into the curriculum is the problem. But more about that later. One could argue that cost is the problem. But that is only partly true. Compared to the cost of chemistry instrumentation such as FTIR, GC-mass spectrometry, and high field NMR, the financial implications of setting up a state-of-the-art computational facility are not excessive. However, as anyone who has been involved in setting up either an instrumental laboratory or a computational laboratory can tell you, there are many hidden costs. Maintenance of the hardware and software and of the network to link the various computers and printers requires a major investment of time and money. 

Fourier transform infrared spectroscopy (FTIR) had its origins in the interferometer developed by Michelson in 1880 and experiments by astrophysicists some seventy years later. A commercial FTIR instrument required development of the laser (1960, by Theodore H. Maiman [1927- ], Hughes Aircraft), refined optics, and computer hardware and software. The Fourier transform takes data collected in time domain and converts them to frequency domain, the normal infrared (IR) spectrum. FTIR provided vasdy improved signal-to-noise ratios allowing routine analyses of microgram samples. 

Hardware. Most low-cost, worktop FTIR spectrometers contain sealed optics. This reduces the effect of water vapour on spectra and protects hygroscopic KBr beam splitters from damage that would occur in high-humidity environments. Sealed optics remove the need for a separate supply of dry air, although the disadvantage is that the sample compartment itself cannot be kept dry and some water vapour will inevitably be manifest in spectra. 

The IR microscope is a valuable tool for the analysis of fibers, particulates, and inclusions. A dedicated microscope-FTIR instrument with appropriate hardware and software to perform a wide range of microscope experiments has been developed recently. 

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