Fourier Transform Infrared (FTIR) analysis is a spectroscopic technique that makes use of the naturally occurring electromagnetic spectrum defined by the wavelengths between 2,500nm and 25,000nm. This is the ‘mid-infrared’ region so you will also hear the method referred to as ‘mid infrared’. Generally though, it is the name of a technique used to convert measurement data into a usable result (Fourier Transform) that is popular, hence, Fourier Transform Infrared, or FTIR for short.
The FTIR advantage
The overall advantages of using FTIR analysis are that it provides rapid analysis data for better decision making in food and agriculture production processes. It is particularly useful for testing liquid samples such as milk and wine. Compared to traditional analysis methods it requires little or no sample preparation and no chemicals or consumables. It is non-destructive, operator friendly, fast, reliable and precise.
How FTIR works
- Light from a broad-band light source containing the full spectrum of wavelengths to be measured is shone through a device called an interferometer.
- The interferometer modifies the light in a special way to allow for subsequent processing of the data
- The beam is passed through the sample where a sample-dependent absorption takes place.
- The light is detected and passed to a computer.
- The computer processes all the data to infer what the absorption is at each wavelength and generates a spectrum corresponding to the data using the Fourier Transform technique.
The infrared analysis technology of choice
FTIR does such a great job that it is often referred to the technology of choice amongst Infrared instrument designers.
Because the spectrums generated by an FTIR analyser are based on many data points, it provides a highly accurate spectral fingerprint of the sample under analysis. In fact, the accuracy and repeatability of results is often at least as good, if not better, than traditional chemical analysis.
The latest FTIR generation instruments are optimised for an excellent signal to noise ratio and the key mechanical parts such as the cuvette where light is shone through a very thin film of the sample are designed to withstand wear that might otherwise cause the optics to drift, for example, the FOSS MilkoScan 7 analyser can test up to 600 milk samples an hour, week after week without adjustment. This is due, amongst other things, to an industrial diamond cuvette at the heart of the analyser. In this respect, FTIR provides a solid platform for standardised instruments and the development of highly stable calibrations that can be used across multiple instruments.
Combining high sensitivity with a full spectrum, FTIR is particularly useful for measuring parameters with low concentrations such as phenolic compounds in grapes that contribute to the colour and flavour of wine. In addition, with many FTIR interferometers scanning the full mid-infrared spectrum and collecting data simultaneously, many parameters can be measured in a single test typically taking just a few seconds.
As an example, just some of the parameters that can be measured from a sample of finished wine with the FOSS WineScan SO2 instrument are: Ethanol, Glucose/Fructose, Malic Acid, Volatile Acid, Total Acid, pH, Free and Total Sulphur Dioxide. The last two parameters mentioned represent a particularly smart application of FTIR because it simultaneously measures liquid wine for most of the parameters and a gas to give the SO2 measurement. SO2 is the most measured parameter in winemaking and traditional analysis takes at least 15 minutes compared to the three minutes with the WineScan SO2.
FTIR analysis units can be used to screen for abnormalities, for example, in a sample of milk to check if it has been accidentally contaminated with cleaning fluids.
Screening milk for abnormalities with FTIR
Another strength of FTIR is that analysis units can also be programmed to screen for abnormalities in a sample, in milk, for example, to check if it has been contaminated with traces of cleaning fluids. The screening is done at the same time as the compositional measurements are performed and no extra equipment or time is required.
It works by testing a sample of milk against a profile for normal milk. Natural raw milk has a particular infrared spectrum – a unique fingerprint. Using FTIR analysis, it is possible to program an analyser to recognise the spectra (or fingerprint) representing pure raw milk. A warning is then given if there is a mismatch. This alerts the user to the need for further testing to determine the nature of the abnormality.
The screening concept introduces a new and convenient testing option for routine milk testing, for example, to screen milk samples for a broad variety of abnormalities, to check whether different milk types are mixed up and to monitor milk for consistent quality of finished dairy products.
Why use anything else: FTIR versus NIR
FTIR spectroscopy is, in principle, very similar to Near Infrared (NIR) spectroscopy, but works at longer wavelengths where the chemical information from the samples is more specific.
While the sensitivity and range offered by the longer wavelengths offers many advantages, it runs into a natural barrier when testing more solid samples. This is because the light can only penetrate a very thin sample (30 -50 um liquid). NIR can depending on wavelength penetrate up to 20 mm of a sample which makes NIR more effective for solid samples.