Infrared Spectroscopy

Infrared Spectroscopy

It is well-known that infrared (IR) is an extremely versatile technology for oil analysis. IR can provide information on a range of oil characteristics, e.g. contamination, breakdown, additive packages, fluid identity, etc. In all of these cases the response of the oil to specific regions in the infrared spectrum is examined and weighted, each being unique to the characteristic being analyzed.

Infrared spectroscopy of lubricants relies on a very simple method. You observe how much Infrared radiation the lubricant absorbs as a function of the frequency of that radiation. Figure 6-1 shows such spectra for typical lubricants. That is all we need from the infrared spectroscopy itself – we just need to make sure that an accurate infrared spectrum is acquired. As you can see in Figure 6-1, different lubricant types and in general different lubricants can have very different spectra. It is these differences we use to turn these spectra into usable information (lubricant properties listed in Table 6-1).

Fourier-Transform Infrared Spectroscopy (FTIR) is a general purpose tool for generating an infrared spectrum that has become widespread across multiple industries, including for oil analysis. In fact, the terms IR and FTIR have become interchangeable for many people. FTIR in general provides a highly accurate infrared spectrum of the sample to be analyzed. However, the FTIR can only generate the IR spectrum. It cannot analyze the spectrum. The value of IR oil analysis come from properly interpreting this spectrum. The same is true in any industry. Spectro Scientific’s focus is on the analysis of the infrared spectrum to deliver quantitative results for oil analysis. This extends down to the hardware utilized for gathering the infrared spectrum: Spectro Scientific uses a grating-based spectrometer in its FluidScan product line, in addition to filter-based spectroscopy for other targeted applications. These approaches specifically target oil analysis, while other approaches are typically used for more general analysis.. The advantages to choosing this approach include enabling rugged, no moving parts, low-power, and miniaturized hardware. Hardware designed specifically for oil analysis must be good enough to gather the infrared spectrum needed for a particular application. Focusing just on specific use cases allows us to design hardware that has other significant advantages, such as ease of use, portability or ruggedness.

As discussed, the power of IR is in the analysis itself, which can examine specific oil analysis properties such as % water, TAN (mgKOH/g), and fluid identity (eg., “it is highly likely that your fluid is Shell Rotella T1”). This is where the Spectro Scientific approach is unmatched in the industry. We have spent years gathering a large library of both infrared spectra and associated chemical properties, currently numbering approximately 700 different oils and greases. The importance of this cannot be overstated: First, it enables users of the FluidScan devices to automatically compare their oil of interest to this library to ensure that they have the correct fluid or even to search the library for similar fluids. Second and perhaps even more importantly, each fluid in the library has been analyzed chemically in order to establish its correlation to laboratory-based techniques for oil analysis. Prominent examples are for acid (TAN/AN) and base number (TBN/BN). This ensures that the FluidScan, when used to analyze a customer’s oil, reports the relevant properties for that oil, and reports them accurately. “Under the hood” are entire families of calibrations that relate (eg., TAN to the infrared spectrum for specific chemical class of oil. These calibrations, as relevant to that particular oil, are attached to each of the 700 oils and greases. For example, there are over 30 TAN calibrations in the library, but each individual oil is assigned a single TAN calibration based on its chemical class. Without this family of calibrations, generated over years of analysis, it would be impossible to provide an accurate TAN value just knowing the infrared spectrum. The same holds true for FTIR or any type of infrared analysis. IR analysis in general can provide information and analysis well beyond standardized methods. The issue has historically been that the methods are limited to a certain set of oils. Spectro Scientific’s multidimensional library approach (oil IR spectrum+chemical properties) eliminates that shortcoming. 

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