Definition
UV-Vis spectrophotometer is an optical analysis instrument that conducts qualitative or quantitative analysis based on the selective absorption characteristics of ultraviolet and visible electromagnetic radiation in the visible region. Its operating wavelength range typically covers 190 nm to 1100 nm and is suitable for the detection of liquid, gas, and solid samples. The instrument has a wide range of application values in environmental monitoring, food analysis, chemical production and materials science.
Principle
The basic principle of the instrument follows Lambert-Beel's law, which describes the linear relationship between absorbance and solution concentration and path length. 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 thickness of the liquid layer. 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 value of the sample by measuring the ratio of the incident light intensity to the transmitted light intensity, and then realizes the analysis of the target component.
Measurement method
Conventional measurement methods include transmission, reflection and absorption. Transmission is suitable for transparent liquid samples, where the sample is placed in a cuvette in the optical path and the transmitted light intensity is directly measured. The reflectance method is mostly used for solid or turbid liquids, and diffuse reflected light is collected by the integrating sphere attachment for detection. The absorption law directly measures how well a sample absorbs light at a specific wavelength. Baseline correction and blank control are required prior to measurement to eliminate background interference from solvents and cuvettes. The scanning mode acquires a continuous spectrum of the sample over a specific wavelength range for qualitative analysis; The fixed-point measurement mode is suitable for quantitative detection of known absorption peaks.
Influencing factors
The accuracy of the measurement results is influenced by several factors. The performance of an optical system, such as light source stability, monochromator bandwidth, and detector sensitivity, directly affects the signal-to-noise ratio and resolution. The nature of the sample itself, including solvent purity, sample concentration range, and the presence of fluorescence or scattering, can cause measurement bias. Environmental conditions such as temperature fluctuations and vibration interference can also cause baseline drift. Among the operational factors, the matching, cleanliness and placement orientation of the cuvette need to be consistent, and the standardization of the sample preparation process is equally important. Regular calibration of wavelength accuracy and absorbance accuracy is necessary to maintain data reliability.
Application:
In the field of environmental monitoring, this instrument can be used for the quantitative analysis of heavy metal ions, nitrates and other pollutants in water bodies. In the food industry, it is often used to determine the peroxide value of food additives, vitamins and fats. The chemical industry uses it for reaction process monitoring and product purity testing. In materials science, it can be used for thin film thickness measurement, band gap analysis of semiconductor materials, and dye performance evaluation. In life science research, it is also used in protein concentration determination and nucleic acid analysis. Applications in different industries need to refer to the corresponding national or international standard methods to ensure compliance and comparability of test results.
Selection
When selecting instruments, it is necessary to comprehensively consider the technical parameters and usage needs. In terms of optical structure, the dual-beam design can compensate for the fluctuation of the light source, and has better baseline stability than the single-beam system. The wavelength range should cover the characteristic absorption band of the substance to be measured, and the resolution index affects the ability to distinguish the closely adjacent absorption peaks. Detector types, such as photomultiplier tubes or silicon photodiodes, have different response characteristics across different wavelength ranges. Sample accessory compatibility, such as microcuvettes, flow cells, or solid sample holders, needs to match the actual sample format. Software features should support the necessary analysis methods and data export formats. In addition, the instrument's maintenance costs, calibration intervals, and supplier technical support capabilities need to be evaluated. Users should make a comprehensive trade-off based on the laboratory's sample throughput, testing accuracy requirements, and budget range.