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Small science! Principles and Spectra of Common Instrumental Analysis
Release time:
2021-05-25 15:27
Instrumental analysis is an analytical method that can directly or indirectly characterize various characteristics of substances (such as physical, chemical, physiological properties, etc.) through probes or sensors, amplifiers, analytical converters, etc., which can be transformed into people's direct perception of known information about material composition, content, distribution or structure. In other words, instrumental analysis is an analytical method that uses the basic principles of various disciplines and uses advanced technologies such as electricity, optics, precision instrument manufacturing, vacuum, and computers to detect the chemical properties of substances.
The analysis object of instrumental analysis is generally the analysis of semi-trace (0.01~0.1g), trace (0.1~10mg) and ultra-trace (<0.1mg) components with high sensitivity, while chemical analysis is generally the analysis of semi-trace (0.01~0.1g) and constant (>0.1g) components with high accuracy.
Instrumental analysis can be roughly divided into: electrochemical analysis, nuclear magnetic resonance spectroscopy, atomic emission spectroscopy, gas chromatography, atomic absorption spectroscopy, high performance liquid chromatography, ultraviolet-visible spectroscopy, mass spectrometry, infrared spectroscopy, and other instrumental analysis.
The principle and spectrum of common instrument analysis are as follows:
1. ultraviolet absorption spectrum UV
Analysis principle: absorption of ultraviolet light energy, resulting in the representation of the transition spectrum of the electron energy level in the molecule: the change of the relative absorbed light energy with the wavelength of the absorbed light
Information provided: the position, intensity and shape of the absorption peak, providing information on the different electronic structures in the molecule
2. fluorescence spectrometry FS
Analysis principle: after being excited by electromagnetic radiation, from the lowest single-line excited state back to the single-line ground state, the emission fluorescence spectrum is expressed by the emission fluorescence energy with the change of light wavelength.
Information provided: fluorescence efficiency and lifetime, providing information on the different electronic structures in the molecule
3. infrared absorption spectrometry IR
Analysis principle: Absorption of infrared light energy, causing vibration and rotational energy level transitions of molecules with dipole moment changes
The representation of the spectrum: the relative transmitted light energy varies with the transmitted light frequency.
Information provided: the position, intensity and shape of the peak, providing the characteristic vibrational frequency of the functional group or chemical bond
4. Raman spectroscopy Ram
Analysis principle: after absorbing light energy, it causes molecular vibration with polarization rate change, and produces Raman scattering spectrum representation method: scattered light energy changes with Raman shift.
Information provided: the position, intensity and shape of the peak, providing the characteristic vibrational frequency of the functional group or chemical bond
5. nuclear magnetic resonance spectroscopy NMR
Analysis principle: in the external magnetic field, the nucleus with nuclear magnetic moment absorbs radio frequency energy and produces the transition of nuclear spin energy level
Representation of Spectra: Variation of Absorbed Light Energy with Chemical Shift
Information provided: chemical shift, intensity, split fraction and coupling constant of the peak, providing information on the number of nuclei, chemical environment and geometric configuration
Instrumental analysis has the following advantages:
High sensitivity: Most instrumental analysis methods are suitable for trace and trace analysis. For example, the absolute sensitivity of atomic absorption spectrophotometry for the determination of certain elements can reach 10-14g。
2. Less sampling quantity: chemical analysis requires 10-1～10-4g, instrument analysis sample often 10-2～10-8g。
The analysis accuracy at low concentration is high: the content of impurities in the range of 10-5% to 10-9% is determined, and the relative error is as low as 1% to 10%.
4. Fast: For example, emission spectroscopy can simultaneously determine 48 elements in water within 1min.
5, can be non-destructive analysis: sometimes can be measured without destroying the sample, suitable for archaeology, cultural relics and other special areas of analysis. Some methods can also carry out surface or micro area analysis, or the sample can be recovered.
6. Can carry out multi-information or special function analysis: sometimes qualitative and quantitative analysis can be made at the same time, and sometimes the composition ratio of materials and the valence state of atoms can be determined at the same time. The radioactive analysis method can also be used for trace impurity analysis.
7, strong specificity: for example, single crystal X diffractometer can be used to measure the crystal structure; ion selective electrode can be used to measure the concentration of specified ions.
8, easy telemetry, remote control, automation: can be used for real-time, online analysis and control of the production process, environmental automatic monitoring and control.
9, the operation is relatively simple: save a variety of chemical operation process. With the improvement of automation and procedure, the operation will be more simplified.
In recent years, the rapid development of instrumental analysis technology in China, widely used in food safety, environmental protection, chemical, pharmaceutical, life science, materials science and other fields, has become a very important qualitative and quantitative analysis method in daily work. However, due to the wide variety of organic compounds, the fragmentation law is complicated and difficult to master. In the absence of spectral analysis ideas and methods, many staff often feel unable to start after getting the spectra. If you need professional laboratory testing services, please contact us!
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