Technology: How Does the IRmadillo Differ to Conventional FTIR?

Fourier transform infrared (FTIR) technology is based on an arrangement of mirrors to split light into two separate paths and then recombine them to create an interference pattern of light (called an “interferogram”). This pattern is fed into the Fourier transform algorithm producing a spectrum that can be interpreted and analyzed.

With conventional FTIR design, this is achieved using a pair of mirrors, where one is static and the other moves along a smooth and well-defined track. This means conventional FTIR instruments can be very sensitive to vibration and movement, as even small vibrations can cause noise or artifacts to appear in spectra as the moving mirror is affected. Manufacturers have managed to reduce the impact of vibration by novel mirror designs, but not completely remove the susceptibility. This means that conventional FTIR instruments can be installed in laboratories or other benign environments, but are often not suitable for industrial installations.

The addition of HeNe lasers into these interferometers as an internal reference have made substantial changes to some aspects of precision, but they do not resolve the weakness to vibration, nor do they affect long-term measurements. In fact, conventional instruments tend to show poor long-term stability, and need re-baselining (called a background or reference scan) fairly frequently. This makes them suitable for short-term reactions and single batches, but can be challenging to use for long-term or continuous manufacturing campaigns.

What about fibers? I’ve heard those mean I can install the instrument far away?

Although some instruments are installed in benign environments using solid “light pipes” directly onto the process of interest, the vast majority of FTIR installations use fiber-optic probes. They are intended to be used to create distance between the instrument and the process (the source of vibration); in reality the average length is about 5 m, so they still require the instrument to be installed relatively near the process. These fibers can give more flexibility on where the instrument can be installed but have a number of drawbacks:

They can be very fragile and easy to break: the fibers themselves are thin and delicate, and can easily be accidentally broken – especially in an industrial environment.
They can be very expensive to manufacture: this means that the cost to install and replace them is very high, potentially adding a higher ongoing cost to instrument ownership if they need repairing or replacing.
They can have very low spectral throughput: which means that the signal in the instrument is very low. This can be partially overcome by installing very sensitive detectors (which often need liquid nitrogen or Stirling engine cooling – another potential point of failure) or a high-powered infrared source (which have shorter lifetimes than lower powered ones).