How does the IRmadillo differ from NIR (near infrared)?
The IRmadillo is based on FTIR technology – which stands for Fourier transform infrared. FTIR uses mid-infrared wavelengths of light (MIR), which are those between 20 and 2.5 µm wavelength. NIR uses near-infrared wavelengths of light (hence the NIR name) which are those of 2.5 to 0.7 µm wavelength. (The “near” in near infrared means light that is very close to the visible wavelengths of light – i.e. those that humans can see). Whilst the distinction between the two wavelengths sounds purely technical, it correlates to very different levels of information:
Mid-infrared light corresponds to fundamental vibrations of molecules which means it can be used to identify specific chemical functional groups of a molecule (i.e. an alcohol appears very different in an infrared spectrum to an ester or an acid). It can also be used to differentiate between very similar molecules as small differences in structure (for example the difference between similar sugars such as sucrose vs. glucose) often give very large differences in the mid-infrared spectrum.
Near-infrared light corresponds to overtones and combinations of vibrations of molecules which means that the quality of information in the spectrum is much poorer, and can be very difficult to interpret. NIR spectroscopy is useful for quantifying and measuring mixtures of molecules that are very different to each other (for example water molecules in slices of meat).
There are two main types of NIR spectrometers:
- FT-NIR: Fourier transform near-infrared spectrometers operate using the same principal as an FTIR spectrometer (read our page comparing the IRmadillo to conventional FTIR spectrometers), but with the difference that NIR fibres are significantly easier to use than MIR fibres. This means using a fibre-optic probe with an NIR spectrometer is a very common approach in industrial environments, and for many applications is a sensible option.
- Dispersive NIR: dispersive instruments use a grating or prism to split light into its constituent wavelengths and map them onto a detector for interpretation. These devices can be very small, and can be very cost-effective spectrometers for very specific applications. They tend to have a very narrow spectral range and fairly low signal-to-noise ratio (SNR) meaning they are designed for relatively simple systems with easy to achieve specifications.
What would we use an NIR for?
NIR instruments have been available for many years, and have demonstrated successes in a multitude of different industries and applications. Some examples where NIR is a common choice are:
- Non-contact measurements of solids: measuring the makeup of solids going into bulk processes (for example protein levels in grain before grinding into flour) is commonly performed using NIR. These can either be laboratory instruments with extractive sampling or continuous on-line measurements in process.
- Water measurements in aprotic solvents: many solvents have very different spectra to water in the near infrared, so measuring water levels with a transmission cell is often easy to achieve with an NIR instrument. Note that solvents with an OH group (such as alcohols) can interfere with water detection using NIR and in this case we would recommend FTIR instead.
What would we recommend choosing the IRmadillo over NIR for?
Although NIR instruments can be fantastic for the right application, there are many applications where they have been tried and the fundamental spectrum type that is obtained is not suitable. Here are some example applications where we feel that the IRmadillo is more suitable:
- Biotechnology and fermentation: industrial biotechnology, fermentation for food, drink and fuel and other similar industries often have very turbid media with both biomass and bubbles. The majority of NIR probes operate using a reflecting mirror and a path length of about 1 cm – which easily gets clogged by particles or scattered by bubbles. The ATR sensing probe of the IRmadillo is almost immune to particles and bubbles. Also, the sugars and organic acids present in biotechnology cannot be easily differentiated and identified by NIR but the IRmadillo can accurately and precisely measure the concentrations of almost every molecule present in a fermentation or cell culture simultaneously.
- Any process with high solid content: NIR instruments tend to have reflectance probes with a slot < 10 mm that is easily clogged or blocked with solids. The IRmadillo is built with an ATR sensing tip which means the probe simply has to be present inside the liquid to be analysed and wetted. As long as liquid is in contact with the ATR-tip of the probe then the IRmadillo will record a measurement. This means that slurries, pulp, hydrolysis tanks, anaerobic digestors, dirty oil streams etc…can be effectively analysed by the IRmadillo regardless of solid content.
- Water in protic solvents (i.e. alcohols): NIR instruments confuse the OH group in an alcohol with the OH in water. The IRmadillo can tell the difference, which means it gives dramatically improved performance for water measurements in protic solvents over NIR. And if the stream also contains other molecules (for example different types of alcohols, or other additives) then the IRmadillo can quantify these as well.