Classification and characteristics of instrumental analysis

Classification of instrumental analysis Although there are many types of instrumental analysis methods, and new methods are constantly being produced, developed and improved, they can be divided into the following four categories according to their basic principles. (1) The optical analysis method is based on the properties of light emission, absorption, scattering, diffraction, polarization, etc.... _ The analysis method is called optical analysis method. Compared with visible-ultraviolet absorption, photometry, infrared spectroscopy, pull-u spectroscopy, emission spectroscopy, atomic absorption spectroscopy, molecular emission, photoanalysis, nuclear magnetic resonance spectroscopy, electron paramagnetic resonance, optical rotation , X-ray diffraction, photoelectron spectroscopy, electron microscopy, etc. (2) The electrochemical analysis method is an analysis method based on the electrochemical properties of the material's resistance, electrical difference, potential, current, and electric quantity, which is called electrochemical analysis. Such as conductance analysis method, potential analysis method, electrolysis and coulometric analysis method, voltammetry and so on. (3) Chromatographic analysis method This is a type of analysis method based on the repeated distribution and separation of the mixture between two immiscible phases in relative motion. According to the state of mobile phase and stationary phase, chromatography can be divided into gas chromatography, liquid chromatography, supercritical fluid chromatography and thin layer chromatography. Chromatography is an important separation and analysis method for modern instrumental analysis. (4) In addition to the above three types of other instrumental analysis methods, there are some special physical or chemical properties for analysis, such as differential thermal and thermogravimetric analysis methods that use the thermal properties of objects for analysis; Radiochemical analysis that uses the properties of radioisotopes for analysis; mass spectrometry that analyzes the properties of positive ions separated by their mass-to-charge ratios in a magnetic field; establishes physical and chemical non-equilibrium in the fluid Flow injection analysis method for measurement under dynamic conditions, etc. In addition, according to the characteristics of the analysis object, Xi’s instrument analysis can be divided into atomic or ion analysis methods, molecular analysis methods, surface and interface analysis methods, and separation analysis methods. The main characteristics of instrumental analysis Although there are many kinds of instrumental analysis methods, each method is often self-contained and has its own basic theory, working principle, instrument and operation method, but they also have certain commonalities. For example, it must involve the basic problem of analysis object, analysis instrument and analysis method; the analysis process usually includes five basic questions: sample collection, sample pretreatment, instrument calibration, sample measurement or characterization, and analysis data processing. Link. The collected samples must be representative, and must not be contaminated, nor should they cause loss of components. in many circumstances. The sample must be pretreated in order to eliminate interference and enrich the components to be tested. The commonly used pretreatment methods are similar to chemical analysis methods, such as digestion, masking, extraction, fractionation, ion exchange, precipitation, etc. Therefore, instrumental analysis is inseparable from chemical knowledge, and chemical analysis is the basis of instrumental analysis. Instrument analysis is a method of relative measurement. Standard materials are needed to calibrate the instrument, and the standard sample is compared with the sample to be tested to obtain the measurement result. The definition of reference materials is usually calibrated by chemical analysis methods. To measure the physical or physicochemical properties of substances often requires specialized instruments. The operator must understand the working principle of the instrument, understand the basic structure, operation method, and test conditions of the instrument. Before using it for the first time, you must be familiar with the instructions of the instrument and operate strictly according to the regulations to avoid damage to the instrument. The general process of instrument analysis and measurement is usually: to generate a physical signal related to the sample (such as light, electricity, sound, heat, magnetism, etc.); through appropriate sensors, the signal is converted into easy transmission, amplification, display or The recorded electrical signal; the weak signal is amplified by an amplifier, and then displayed and recorded; finally, the recorded data is analyzed and processed to obtain the measurement result. This book will introduce some of the most commonly used instrumental analysis methods. The common advantages of these methods are high sensitivity, good selectivity, fast analysis speed, and small sample amount. But their relative error is generally more than 1%. For the analysis of constant components with a content of more than 1%, it is not as accurate as the chemical analysis method, and for trace components with a content of 1% to 0.01% and those with a content of less than 0.01% Trace analysis is much more accurate than chemical analysis. When learning instrument analysis, you should understand the basic principles of each method, master the relevant basic concepts and basic methods, understand the basic structure, operation methods and test conditions of the instrument; at the same time, pay attention to understanding and comparing each method. The scope of application, advantages and disadvantages, limitations and causes of measurement errors; in addition, various instrumental analysis data processing methods must also be focused on. Instrumental analysis is a very experimental course. You should cherish the opportunity of the experiment, carefully preview, understand the principles of the experiment, and be clear about the experimental procedures; observe carefully in the experiment, be diligent in thinking, combine theories, use both hands and brains, and strive to improve your ability to analyze and solve problems. In short, instrumental analysis involves a wide range of knowledge, which determines the difficulty of learning instrumental analysis courses; there are many types of instruments, which determine its complexity; many instruments are relatively advanced, complex, and expensive. It determines its mystery; its application is very wide. It is an indispensable and powerful weapon in many fields such as production, life and scientific research, which determines its importance and practicality. In learning, we should take these characteristics into consideration.

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