Spectrometer, also known as spectrometer. A device that measures the intensity of spectral lines with photodetectors such as photomultiplier tubes at different wavelengths. Its structure consists of an entrance slit, a dispersion system, an imaging system and one or more exit slits. The dispersive element is used to separate the electromagnetic radiation of the radiation source into the required wavelength or wavelength region, and the intensity is measured at the selected wavelength (or scanning a certain band). Divided into two types of monochromator and multicolor meter.
The following introduces the working principles of several spectrometers commonly used in laboratories. They are: fluorescence direct reading spectrometer, infrared spectrometer, direct reading spectrometer, and imaging spectrometer.
The principle of fluorescence direct reading spectrometer:
When a high-energy X-ray with an energy higher than the binding energy of the inner electron of the atom collides with the atom, an inner electron is expelled and a hole appears, leaving the entire atomic system in an unstable excited state. ) -12- (10) -14s, and then spontaneously transition from a state of high energy to a state of low energy. This process is called the emission process. The emission process can be either a non-radiative transition or a radiative transition.
When the electrons in the outer layer transition to the hole, the energy released is then absorbed inside the atom to expel another secondary photoelectron in the outer layer.This is called the Auger effect, also known as the secondary photoelectric effect or no Radiation effect, the expelled secondary photoelectrons are called Auger electrons. Its energy is characteristic and has nothing to do with the energy of incident radiation. When the electrons in the outer layer jump into the holes in the inner layer, the energy released is not affected by the atoms. Absorption, but emission in the form of radiation, produces X-ray fluorescence, whose energy is equal to the energy difference between the two energy levels. Therefore, the energy or wavelength of X-ray fluorescence is characteristic and has a one-to-one correspondence with the elements.
After the K-layer electrons are expelled, their holes can be filled with any electrons in the outer layer, and ad4yjmk can thus generate a series of spectral lines, called K-line spectral lines:
The X-rays radiated from the L-layer transition to the K-layer are called Kα rays, and the X-rays radiated from the M-layer transition to the K-layer are called Kβ rays.Likewise, the L-layer electrons are expelled to produce L-series radiation. If the incident X-ray makes a certain After the K layer electrons of the element are excited into photoelectrons, the L layer electrons transition to the K layer.At this time, the energy ΔE is released, and ΔE = EK-EL. This energy is released in the form of X-rays, and the Kα rays are generated. Can produce Kβ rays, L series rays, etc.
HGMoseley found that the wavelength λ of the fluorescent X-ray is related to the atomic number Z of the element, and its mathematical relationship is as follows: λ = K (Zs) -2 This is Moseley ’s law, where K and S are constants, Therefore, as long as the wavelength of the fluorescent X-ray is measured, the type of the element can be known, which is the basis of the qualitative analysis of the fluorescent X-ray. In addition, the intensity of the fluorescent X-ray has a certain relationship with the content of the corresponding element, according to which, it can be carried out Elemental quantitative analysis.
The principle of infrared spectrometer:
Infrared spectroscopy is closely related to the molecular structure and is an effective method to study and characterize the molecular structure. Compared with other methods, infrared spectroscopy is recognized as an important analytical tool because it has no restrictions on the sample. In the analysis and determination of molecular configuration and conformation research, chemical engineering, physics, energy, materials, astronomy, meteorology, remote sensing, environment, geology, biology, medicine, medicine, agriculture, food, court identification and industrial process control, etc. All have a very wide range of applications.
Infrared spectroscopy can study the structure and chemical bonds of molecules, such as the determination of force constants and molecular symmetry. The infrared spectroscopy method can be used to determine the bond length and bond angle of molecules, and to infer the three-dimensional configuration of molecules. According to the obtained force constant, the strength of the chemical bond can be inferred, and the thermodynamic function can be calculated from the normal frequency. Some groups or chemical bonds in the molecule correspond to band wave numbers in different compounds that are basically fixed or only change in a small band, so many organic functional groups such as methyl, methylene, carbonyl, cyano, Hydroxyl groups, amine groups, etc. have characteristic absorption in the infrared spectrum. Through infrared spectrum measurement, one can determine which organic functional groups are present in the unknown sample, which lays the foundation for the final determination of the chemical structure of the unknown.
Due to intramolecular and intermolecular interactions, the characteristic frequency of organic functional groups will change slightly depending on the chemical environment in which the functional groups are located, which creates conditions for the study and characterization of intramolecular and intermolecular interactions.
Many normal vibrations of molecules in the low wave number region often involve all atoms in the molecule. Different molecules vibrate in different ways from each other, which makes infrared spectroscopy highly characteristic like fingerprints, called fingerprint region. Taking advantage of this feature, people have collected infrared spectra of thousands of known compounds and stored them in a computer to compile a standard spectral library of infrared spectra.
One only needs to compare the measured infrared spectrum of the unknown with the spectrum in the standard library to quickly determine the composition of the unknown compound.
The development of contemporary infrared spectroscopy technology has made the meaning of infrared spectroscopy far beyond the stage of simple routine testing of samples and inference of the composition of compounds. The combination of infrared spectrometer and many other testing methods has led to many new molecular spectroscopy fields. For example, the combination of chromatographic technology and infrared spectrometer has created opportunities to deepen the understanding of the chemical structure of various components in complex mixture systems; The combination of microscope methods to form infrared imaging technology is used to study the morphological structure of heterogeneous systems. Because infrared spectroscopy can use its characteristic band to effectively distinguish different compounds, this method has a chemical contrast that is difficult to match with other methods.
The principle of direct reading spectrometer:
The direct reading spectrometer uses the principle of atomic emission spectroscopy. The sample is excited into an atomic vapor by arc or spark discharge. The atoms or ions in the vapor are excited to produce an emission spectrum. The emission spectrum enters the spectrometer's spectroscopic chamber through the optical fiber and is dispersed into various spectral bands. According to the emission wavelength range of each element, the best spectral line of each element is measured by the photocell. The intensity of the spectral line of each element is proportional to the content of the element in the sample. The content can be determined by an internal pre-made calibration curve, directly in percentage concentration display.
In fact, you do n’t need to talk about a noun. The direct name of a direct-reading spectrometer is the atomic emission spectrometer. The reason why it is called direct-reading is that compared to the spectrograph and the early emission spectrometer, because there was no computer before the 70s All current signals converted by photoelectricity are read by digital tube, and then the curve is drawn on logarithmic conversion paper and the content value is calculated. After the application of computer technology in the spectrometer, all data processing is completed by the computer and can be directly converted Content, so it ’s more direct to read the results, but it ’s called direct reading for short. There is no such concept abroad.
The direct-reading spectrometer is a spark spectrum. Aoqiu instrument is mainly recommended for the analysis of bulk or strip metal samples. ICP uses liquid sampling, which has a wide range of applications and spectroscopic devices.
As long as the direct reading spectrometer is normally cleaned and maintained, there is no problem with the curve. It is very convenient to use. It is very quick to make a sample. After the sample is polished, the result will be produced upon excitation. ICP-AES should be slow to do once. The difference between them should be that the sample preparation method is different. The principle is similar. The direct reading uses the emission spectrum, and the ICP absorbs the spectrum.
Imaging spectrometer:
Imaging spectroscopy is to obtain continuous spectral images of ground features at a high spectral resolution in a specific spectral domain. This allows remote sensing applications to perform spatial expansion on the spectral dimension and quantitatively analyze the biophysical and chemical processes and parameters of the earth ’s surface.
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