Definition
UV-Vis spectrophotometer is an optical instrument that analyzes the selective absorption characteristics of electromagnetic radiation in the ultraviolet-to-visible region based on matter. Its operating wavelength range usually covers 190 nm to 1100 nm, which is suitable for qualitative identification and quantitative determination of liquid or solid samples, and has a wide range of application value in many fields such as environmental monitoring, food safety, materials science and chemical production.
Principle
The basic principle of the instrument follows Lambert-Beale's law, which describes the quantitative relationship of matter to the absorption of monochromatic light. When a beam of parallel monochromatic light passes through a homogeneous medium, the absorption of light by the medium is directly proportional to the concentration of the absorbing substance and the length of the optical path. Its mathematical expression is:
A = εbc
Among them, A represents absorbance, ε is the molar absorbance coefficient, b is the length of the optical path, and c is the concentration of the absorbing substance. The instrument calculates the absorbance of the sample by measuring the ratio of incident light intensity to transmitted light intensity, and then completes the quantitative analysis based on the above relationship.
Measurement method
Conventional measurement methods mainly include transmission method and reflection method. Transmission methods are suitable for transparent or translucent liquid samples, where the sample is placed in a cuvette in the optical path and the transmitted light intensity is directly measured. The reflection method is commonly used for opaque samples such as powders and solid sheets, and is analyzed by measuring the diffuse reflected light signal on the sample surface. In addition, according to different scanning methods, it can be divided into fixed wavelength measurement and full-wavelength scanning, which can obtain the complete absorption spectrum of the sample in a specific wavelength range, and is often used for substance identification and reaction process monitoring.
Influencing factors
The accuracy and repeatability of measurement results are affected by a variety of factors. Factors of the instrument include light source stability, monochromator bandwidth, detector sensitivity, and the degree of aging of the optical components. Sample-related factors include solvent selection, sample concentration range, cuvette cleanliness and matching, and possible scattering interference from suspended particles. Environmental conditions such as temperature fluctuations and external stray light interference also need to be controlled. Ensure that the sample concentration is within a linear range and that the instrument is calibrated regularly using reference materials.
Application:
The instrument is widely used in industry and scientific research. In environmental analysis, it can be used to determine the chemical oxygen demand, heavy metal ions and nitrate content of water. Food safety is commonly used to detect food additives, colors, and nutrients. In chemical production, it is used to monitor reactant concentrations and product purity. In materials science research, it is used to characterize the optical properties and film thickness of semiconductor materials and nanoparticles. Its non-destructive, easy operation and good sensitivity make it one of the basic equipment of conventional laboratories.
Selection
When selecting instruments, it is necessary to comprehensively consider the technical parameters and usage needs. Core parameters include wavelength range, spectral bandwidth, photometric accuracy, stray light level, and scanning speed. Depending on the sample throughput, you can choose between single or double beam models with manual injection, or a system with an automated sample stage. For applications that require kinetic studies, attention should be paid to the temporal resolution and data processing capabilities of the instrument. In addition, the instrument's software capabilities, scalability (e.g., accessory support such as integrating spheres, micro sample cells, etc.), and ease of maintenance are also important considerations. It is recommended to conduct a comprehensive evaluation based on the specific experimental purpose, sample characteristics and budget range.