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Infrared spectroscopy has been used for over 100 years, and it has become a robust method, relied upon by numerous applications to identify samples and detect impurities within them, as well as to carry out quantitative assessments.
Due to the incredible flexibility of the technique, a wide range of samples, both organic and inorganic, can be suitable for study. In addition to this, as the method has developed, little preparation procedure is required, meaning that the “ideal sample” is easy to achieve.
Identifying the “fingerprint” of a substance
The technique of infrared spectroscopy is widely used in many research scenarios, as well as in industry. It has applications in chemical analysis, forensics, and environmental testing, among others.
Infrared spectroscopy is mostly used to gain qualitative information, but it can also be used quantitatively. It is most frequently operated to identify samples, conducting quantitative analyses, or detecting impurities in those samples.
The method works through reading the characteristic “fingerprint” that is produced by compounds. Each compound provides a specific and unique spectrum of vibrations when a beam of radiation (in the form of infrared light of the electromagnetic spectrum) is passed through it. The characteristic vibrations, induced by the light form patterns of peaks, can be read by infrared spectroscopy to identify the substance in the sample.
Speed, reliability, accuracy, and convenience make the technique appealing and easy to adopt by analysts in various settings. In addition, the method is both cost and time-effective, as well as requiring little in terms of labor.
Samples used in infrared spectroscopy
The samples that infrared spectroscopy can measure are vast. Samples can be in the form of gas, liquid, or solid, and the process can be carried out on either inorganic or organic tissues as it is a non-destructive technique.
Common samples that are studied with infrared spectroscopy include, but aren’t limited to, organic materials such as adhesives, fats, sealants, paints, plastics, rubbers, resins, oils, waxes, and pure or mixed solvents.
Modern techniques require little in terms of sample preparation - some versions of the method need almost no preparation at all, therefore, creating “ideal samples” is reasonably straightforward for current infrared spectroscopy methods. This reduction in preparation time also adds to the technique’s time and cost-saving advantages.
As discussed, minimal preparation is required to enable a sample to be viable for study. Solid samples are usually prepared on thin plates, whereas powder samples are often pressed into pellets and sometimes diluted. Diamond dust or high‐density polyethylene (HDPE) are often suitable to be incorporated. Liquid samples are usually prepared in what is referred to as a sandwich - a drop of the liquid sample is added to a polished salt plate, with a second plate placed on top to spread out the sample.
More specific research applications occasionally require more stringent preparations to create the ideal sample. However, for some applications, the ideal sample is unknown. For example, the diagnosis of some diseases relies on the analysis of biofluids, such as serum and plasma. In these circumstances, research is still being conducted to understand the optimal sample and technique for acquiring the most reliable and accurate results.
Finally, the ideal sample can vary dependent on the technique being used, as this informs the sample preparation required to give the best results. The nature of the sample itself, such as its size and condition, can alter the preparation techniques required to convert it into an ideal sample.