Fourier Transform Infrared (FTIR) Spectroscopy

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Spectroscopy is a technique for identifying the chemical design of materials. There are many different types of spectroscopy, but one of the most common is Fourier Transform Infrared (FTIR) Spectroscopy. You can use FTIR spectroscopy to identify a wide range of chemicals, including hydrocarbons, polymers, and proteins. In addition, you can also use FTIR spectroscopy to measure the concentration of these chemicals in a sample. This makes FTIR spectroscopy an essential tool for lubricant analysis.

What is Fourier Transform Infrared Spectroscopy?

Fourier Transform Infrared (FTIR) Spectroscopy is a powerful analytical tool for identifying and characterizing materials. By measuring the infrared radiation absorbed by a sample, FTIR spectroscopy can provide information about the chemical composition and structure of the material. This makes FTIR spectroscopy a valuable tool for identifying unknown substances and determining the properties of materials.

How Does FTIR Work for Lubricant Analysis?

Fourier transform infrared spectroscopy is a versatile method for detecting lubricant contaminants, additives, and lubricant degradation byproducts. Despite its widespread use, many people do not fully understand how it works for assessing multiple lubricant characteristics.

Every molecule absorbs radiation at specific wavelengths. A detector on the other side of a sample identifies molecules based on what radiation passes through. Each molecule produces a different pattern or wavelength, just like a fingerprint. So, the material composition of samples can be determined using this method. This makes qualitative analysis easier, and labs typically use a software algorithm to visualize the spectrum.

FTIR spectroscopy is a relatively fast test method. It is capable of simultaneously detecting antioxidants, oxidation, fuel, water, glycol, soot, and certain additives. Further, the size of the spectrum peaks directly relates to the amount of a specific material present in the sample, which enhances the power of this qualitative measurement.

FTIR is Actually a Mathematical Process

As the radiation enters the sample, some frequencies are absorbed. An energy detector measures the energy emitted by the sample. After measuring the signal, it goes to a computer for Fourier transformation. A Fourier transformation is a mathematical method for alternately representing a waveform for easier viewing. This enables a technician to review results and make a quick analysis.

FTIR Useful for Identifying Cross-Contamination

Identifying major changes in lubricant chemistry, such as those from cross-contamination of two oils with various chemical compositions, is another area where FTIR can be very helpful. You can verify this unintentional mixing by recording the FTIR spectrum of the suspected blend alongside the pure oil samples’ reference spectra. It’s generally advisable to conduct an FTIR spectrum as soon as possible in conjunction with a brand-new, fresh oil reference whenever you anticipate a contamination problem.

The Downside of Fourier Transform Infrared Spectroscopy

Typically, the infrared spectrum of used lubricant samples is complex and can be difficult to interpret with any degree of certainty since some wavenumbers may overlap. The complexity is because most lubricant samples contain a mix of thousands of molecules, including base oil molecules, additives, degradation byproducts, wear debris, and contaminants. Although it has its drawbacks, FTIR remains one of the most commonly employed screening tools in lubricant analysis labs.

FTIR analysis of used oil samples is a three-stage process that minimizes the effects of base oil and additive molecules. To obtain a baseline FTIR trace, the first step is to record the FTIR spectrum of a new oil sample. As a second step, the FTIR spectrum of the used oil sample is recorded.

Finally, the difference spectrum is obtained by subtracting the new oil baseline from the used oil spectrum, also called the new oil reference. It is theoretically possible to measure the differences in both the chemical composition of the oil, including changes associated with oxidation, and any contaminants without interference from the new oil molecular resonances by using the difference spectrum.

However, it is not practical to send a sample of new oil along with a sample of used oil for every round of lubricant testing. A new oil reference must match the type, brand, grade, and batch of the used oil for the procedure to be accurate.

Fourier Transform Infrared Spectroscopy: Worthy of Every Lubricant Analysis Program

In any lubricant analysis program, FTIR is a valuable tool. Utilizing this technique in conjunction with other standard test methods and strategies can provide oil analysts and end users with a vast amount of information. We hope that this article was helpful in your understanding of how the test works and what it can contribute to your organization.

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