Spectroscopic analysis

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Spectroscopic analysis

Spectroscopic analysis is an analytical method based on measuring the spectrum of a substance. The spectrum is an image in which complex color light is split by the dispersion system and arranged in order of wavelength or frequency. Quantitative structural information can be obtained by analyzing the wavelength and intensity of the emitted, absorbed or scattered radiation produced by the transition between the atoms’ quantized energy levels within the material. Depends on the source of radiation, origin of atoms and types of structural information obtained, there are different types of spectrometry developed in materials analysis.

Atomic Emission Spectrometry (AES)

A substance is excited by electric, thermally induced or photo excitation to obtain energy and generate an excited atom or molecule. An emission spectrum is generated when transitioning from an excited state to a low energy state or a ground state. The emission spectrum of includes X-ray fluorescence spectrum, atomic emission spectrum, atomic fluorescence spectrum, molecular fluorescence spectrum, phosphorescence spectrum and chemiluminescence method. Spectral analysis is to detect characteristic X-ray, ultraviolet, visible, atomic, phosphorescent, visible light signals.

Atomic emission spectroscopy has applications in many fields. In the application of environmental samples, the sample is atomized into an aerosol and then taken into the inductively coupled plasma (ICP) for measurement. It can detect important indicators of environmental protection, and it is fast, accurate and easy to operate. For the analysis of metallurgical raw materials, it is possible to consume less components to be tested and to simplify the processing of the dissolved samples. Besides elemental analysis in food, in biological samples, it is also used in petrochemical, polymer materials, medical testing, etc.

Atomic absorption spectrometry (AAS)

An absorption spectrum is produced when the electromagnetic radiation absorbed by a substance satisfies the energy required for the transition between the two energy levels of the atomic nucleus, atom or molecule of the substance.

Atomic absorption spectroscopy has a wide range of applications in polymer material, metal material, food and drug, and environmental analysis. For example, analyze the residual of the catalyst in the polymer material, determine the content of many metal ions in the metal materials. Some elements in environmental monitoring studies, food and medicines can also be analyzed and determined by atomic absorption spectrometry.

Ultraviolet-visible spectrometry (UV-Vis)

Ultraviolet–visible spectroscopy refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible spectral regions. In these regions of the electromagnetic spectrum, atoms and molecules undergo electronic transitions. Absorption spectroscopy is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the excited state to the ground state, while absorption measures transitions from the ground state to the excited state. Molecules having non-bonding electrons can absorb the energy in the form of UV or visible light to excite these electrons to higher molecular orbitals.

UV-Vis spectroscopy is a widely used analytical tool for pharmaceutical, medical, materials, chemical, environmental, geological, mechanical, metallurgical, metrology, petroleum, food, biological, agricultural, forestry, fisheries. research, teaching work. qualitative analysis, purity check, structural analysis, determination of complex composition and stability constant, and reaction kinetics can be performed.

Infrared spectroscopy (IR)

Infrared spectroscopy is due to vibrational transitions of molecular energy levels. The infrared absorption spectrum can be used to speculate which functional groups the organic compound contains, and the possible structure of the unknown compound. Infrared spectroscopy is simple to operate, and the characteristics of the spectrum are strong. The structure of the polymer material can be analyzed and identified. The most straightforward method for qualitative analysis is to compare the infrared spectrum of the sample in the infrared spectroscopy library.

Fluorescence spectroscopy

A fluorescence spectrophotometer is an instrument used to scan the fluorescence spectrum emitted by a liquid phase fluorescent label. Spectrophotometers are widely used in the analysis of inorganic and organic materials due to the high sensitivity and wide dynamic linear range. In the inorganic element analysis, the content of the element is determined mainly by the complex of the element to be tested and the organic reagent or by the fluorescence quenching effect. Many methods have been developed for clinical, food nutrition and additives analysis. Such as laser-induced fluorescence method for the diagnosis of malignant tumors, micro-fluorescence method to study the interaction between drugs and cells, DNA sequencing and the determination of the content of fluorescence.

Nuclear magnetic resonance spectroscopy (NMR)

NMR is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic field and the NMR signal is produced by excitation of the nuclei sample with radio waves into nuclear magnetic resonance, which is detected with sensitive radio receivers. An atomic nucleus placed in a strong magnetic field undergoes energy level splitting. When the absorbed radiant energy is equal to the energy level difference, energy level transition occurs and generates a nuclear magnetic resonance signal. The intramolecular magnetic field around an atom in a molecule changes the resonance frequency, thus giving access to details of the electronic structure of a molecule and its individual functional groups.

NMR is a powerful non-destructive technique to determine the structure of organic matter. From the continuous wave nuclear magnetic resonance spectrum to the pulsed Fourier transform spectrum, from the traditional one-dimensional spectrum to the multi-dimensional spectrum, the technology is continuously developed and the application field is keeping extended. For example, NMR has been used in the qualitative analysis of the copolymer composition, based on the principle that the peak area is proportional to the number of resonance nucleus, the composition of the copolymer, and the molar ratio of the two components can be calculated by measuring the area and total area of each proton absorption peak.

Mass Spectrometry (MS)

Mass spectrometry usually uses high-energy ion beams (such as electrons) to bombard the vapor molecules of the sample, destroy the valence electrons in the molecule, and form positively charged ions. These ions are then separated according to their mass-to-charge ratio, for example by accelerating them and subjecting them to an electric or magnetic field: ions of the same mass-to-charge ratio will undergo the same amount of deflection. The ions are detected by a mechanism capable of detecting charged particles, such as an electron multiplier. Results are displayed as spectra of the signal intensity of detected ions as a function of the mass-to-charge ratio. The atoms or molecules in the sample can be identified by correlating known masses (e.g. an entire molecule) to the identified masses or through a characteristic fragmentation pattern.

Mass spectrometry can be combined with nuclear magnetic resonance spectroscopy and infrared spectroscopy to analyze the structure of complex compounds and play a very important role in the identification of organic molecules. Gas chromatography-mass spectrometry (GC-MS), Liquid chromatography-mass spectrometry (LC-MS), which combines the efficient separation of chromatographic techniques with the identification of mass spectrometry, has been widely used especially in analytical chemistry, biochemistry and environmental science. Thermogravimetry-mass spectrometry (TG-MS) overcomes the disadvantage of thermogravimetric analysis that can not detect the volatile components of the system during the heating process, which brings certain difficulties to study the reaction process and explain the reaction mechanism. The fragment-free method during ionization in MS is one of the effective methods to distinguish the evolved mixture gases generated simultaneously in real-time. TG-MS has become increasingly popular in the analytical laboratory.


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