Detailed Understanding, Samples, and Principle of IR Spectroscopy
IR Spectroscopy stands for Infrared Spectroscopy and as the name suggests, is involved with light particles. Light is spread across a spectrum, with infrared rays being at the extreme end of it since it has a frequency that is much less than that of visible light. Infrared Spectroscopy deals with the understanding of how one molecule interacts with infrared light or behaves under the influence of infrared light.
IR Spectroscopy is widely used in the fields of inorganic and organic chemistry in order to see how molecules interact and what they essentially do. Infrared light can be used to see these particles which are otherwise not visible to the human eye.
What Does Infrared Spectroscopy Mean?
An IR spectrum refers to a graph that is plotted keeping the infrared light absorbed on the Y-axis against the wavelength or frequency that is plotted on the X-axis. This is then used in IR Spectroscopy to determine exactly how a given molecule absorbs the infrared light if they correspond to vibrations that are present in the bonds of that molecule.
The light frequency of infrared light matches the bond frequency that is inside these molecules. This has a number of very potent applications in today’s life as well, and it facilitates a lot of industrial processes.
Regions of the Infrared Spectrum
The infrared spectrum can be essentially divided into near, mid, and far regions, based on how they are related to the visible spectrum. The high energy and near IR region have 0.8-2.5 μm wavelengths or 14000-4000 cm-1 and can lead to harmonic or overtone vibration. The mid-IR region on the other hand has a 2.5-25 μm wavelength or 4000-400 cm-1 and can help in studying fundamental vibrations as well as associated rotational vibrational structure. The far IR region is right next to the microwave region and has 25-1000 μm wavelengths or 400-10 cm-1. Being low energy, this is useful for rotational spectroscopy.
The regions of the infrared spectrum can also be classified in a different manner than what is mentioned above. Meaning, the region from 4000 cm-1 to 1300 cm-1 comprises bands that help identify an unknown compound’s functional group. And the region from 1300 cm-1 to 400 cm-1(also known as fingerprint region) features bands that are unique to every molecule, just like a fingerprint. These bands are useful for comparing a particular compound’s spectra with another.
Samples in Infrared Spectroscopy
IR spectroscopy can make use of samples in different physical states, such as solid, liquid, and gas. The methods of sample preparation are different for each and are elaborated below:
Solid sample-
Solid Film Technique– Appropriate for amorphous solids, this technique involves melting of the sample and then cooling and depositing it like a thin film on the KBr cell.
Solid run in Solution Technique– The sample must be dissolved in solvents like carbon tetrachloride, carbon disulfide, or dichloromethane to prepare a concentrated solution. This solution is then spread on KBr plates as a thin film for scanning. Do note that no infrared radiation should be absorbed by the solvent.
Pressed Pellets Technique– Pellets of the sample and KBr (dry KBr powder must be crushed for this) need to be prepared in this technique. The sample concentration in KBr can range from 0.2 to 1%. The mixture of sample and KBr then must be transferred to a die set, where a hydraulic press will put pressure and create compressed pellets.
Mull Technique – The powdered sample is combined with nujol agent or mineral oil in this method and mulled to create a paste. This is then applied to the NaCl, AgCl, or KBr plates.
Liquid Sample- There is no need to mix liquid samples with any solvent since solvents have an absorption spectrum of their own and can interfere with correct results. Highly polished salt plates of KBr, NaCl, or AgCl are used to scan the sample, which is placed in the form of a drop and spread like a thin film.
Gas Sample- For a gaseous sample, a specially designed cell made of KBr and NaCl is used. This has a 5 to 10 cm path length. The gaseous vapors are placed in the cell and the cell is then positioned in the path of infrared radiation.
What is the Principle Behind Infrared Spectroscopy?
There are some common principles that govern the understanding of IR Spectroscopy. It is understood that atoms that make up a molecule are connected together by chemical bonds. The application of infrared light to any molecule makes the atoms in it vibrate with energy, and after a point, the natural frequency of vibration is equal to the infrared frequency. At this stage, the infrared light gets absorbed, and this point is marked.
Apart from understanding the IR principle, understanding the IR spectroscopy instrumentation is also very helpful for researchers. This involves splitting an IR light beam into two and passing them through the sample and reference. Both these beams are then reflected so that they pass through a splitter and detector in sequence. Once the processor interprets the data that passes through the detector, the final reading is printed.
FAQs on IR Spectroscopy
1. What are some of the limitations of IR Spectroscopy?
While this process has a lot of benefits, it also comes with a certain degree of limitations on it. For example, the foremost limitation is that it is not possible to calculate the molecular weight of any item by using IR Spectroscopy. IR Spectroscopy also does not shed any light on the relative positions that are maintained by the functional groups of the molecule. Another very striking limitation is that IR Spectroscopy does not stick to Beer’s law of complexity spectra.
2. What are the practical applications of Infrared Spectroscopy?
This process is important in the fields of inorganic and organic chemistry, as mentioned, for a number of reasons IR Spectroscopy has many applications in industries. In fact, it is also very useful in the field of forensic studies as well as crime lab analysis. Quantitative analysis of particles is a very potent application of IR Spectroscopy. In addition to this IR Spectroscopy can also be used to test for the likelihood of resemblance in two different molecules to see if they are identical or not.
3. Is it possible for IR Spectroscopy to find impurities in a substance?
Yes, this is also a very well-known application of IR Spectroscopy in industrial and other miscellaneous purposes. Infrared light can be used to check if a substance is pure or has impurities in it, and this is one by noting how the molecules react. Infrared light can be passed through the standard compound to check how it behaves, and then tested on the compound in question. Any spike in behavior would indicate that there are impurities present in the compound since it was already tested on the original pure compound.
4. Does infrared light have any color?
The term has the word red in it, but this does not, however, mean that infrared light is red in color. It just lies at the extreme end of the electromagnetic spectrum. In fact, infrared light is not visible to the naked eye, so no one can really tell if it is red in color. However, for scientists and researchers, infrared light does have a certain color-which is mostly between 1 and 700 nm in wavelength. Light is not measured in terms of visible color but rather based on its wavelength and position on the electromagnetic spectrum.
5. Is infrared light harmful to health?
Technically speaking, we are always exposed to some degree of infrared light since it is included in the spectrum of light. This amount is not likely to cause any real effect, however. In case someone is prolonged to infrared light only and in a much higher concentration, then they certainly run the risk of suffering from a number of health problems. Vision damage is one of the main harmful effects of overexposure to infrared light. It can cause permanent damage to the retina and cornea and this is why people who work with infrared light wear protective glasses.
