Issues for consideration in the implementation of process IR

Maintenance issues are important to address, and high-cost replacement parts must be kept to a minimum, unless the frequency of replacement is only once every 3—4 years. Today, process FTIR analyzers are not necessarily a problem, as long as components are simple to replace. The normal replacement items are the source and laser, and the replacement of these must be kept simple. If an interferometer alignment is required, then this must be automated via an integrated mechanized auto-align procedure. 

One aspect that has limited the use and introduction of process analyzers, and in particular FTIR analyzers, has been the high cost of the analyzer, and the resultant high cost per analysis point. Many process analyzer installations are financially evaluated in terms of cost per analysis or analysis point, as well as a payback. Typically, this needs to be kept as low as possible. 

The use of fiber optics and fiber-optic multiplexing can increase the number of analysis points, and hence can reduce the overall costs related to a single analyzer. This approach has been used successfully with NIR instrumentation, where typically up to 8 points can be handled. As noted earlier, the use of fiber-optics with mid-IR Fourier transform instruments has been limited. Although in the past commercial multiplexers have been available for mid-IR fiber systems, their use has been minimal. 

The opportunity to reduce the cost per analysis point can be very important for certain applications. One option with FTIR is to use sample stream multiplexing with a manifold system. For gas-based systems this is very straightforward, and does not impose high overhead costs. Liquid systems are more complex, and are dependent on the nature of the stream involved, and material reactivity, miscibility, and viscosity are important factors to consider. As noted previously, with the introduction of new, miniaturized technologies, the hope is that newer, less-expensive devices can be produced, and these can provide the needed multiplicity to reduce the cost per analysis point to an acceptable level. 

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