Definition
A fluorescence spectrophotometer is an analytical instrument used to measure the fluorescence properties of a substance. It enables qualitative or quantitative analysis of substances by detecting the fluorescence signal emitted by a sample under the excitation of light at a specific wavelength. The instrument is widely used in materials science, environmental monitoring, food safety, and industrial quality inspection.
Principle
The working principle of fluorescence spectrophotometers is based on the phenomenon of photoluminescence. The instrument typically consists of a light source, a monochromator, a sample chamber, a detector, and a signal processing system. The excitation light emitted by the light source is split by a monochromator, and the irradiated sample makes its electrons transition to the excited state, and then returns to the ground state to emit fluorescence with a wavelength longer than the excitation light. The emitted light is split by another monochromator and received by the detector, and finally converted into an electrical signal output.
The relationship between fluorescence intensity and substance concentration can be expressed by the formula:If = kΦI0εbc, among themIfis the fluorescence intensity,kis the instrumental constant,Φis the fluorescence quantum yield,I0To excite the intensity of the light,εabsorbance coefficient for molarity,bfor the optical path,cis the sample concentration.
Measurement method
Common measurement modes include emission spectral scanning, excitation spectral scanning, and simultaneous fluorescence scanning. Emission spectral scanning is to record the change of emission fluorescence intensity of the sample with wavelength at a fixed excitation wavelength. Excitation spectral scanning is to record the change of fluorescence intensity with excitation wavelength at a fixed emission wavelength. Simultaneous fluorescence scanning is measured by changing the excitation and emission wavelengths at the same time. Quantitative analysis usually uses the standard curve method to establish a linear relationship between fluorescence intensity and concentration through a series of standard solutions.
Influencing factors
Instrument measurements are influenced by a variety of factors. In terms of optical systems, light source stability, monochromator bandwidth, and detector sensitivity affect the signal-to-noise ratio. Sample factors include solvent polarity, temperature, pH, and coexisting species that can cause fluorescence quenching or enhancement. In addition, too high a sample concentration can cause the fluorescence intensity to deviate from the linear relationship between concentration due to internal filtration effects. During operation, parameters such as slit width and scanning speed should be controlled to ensure data reliability.
Application:
In the environmental field, it can be used to detect organic pollutants such as polycyclic aromatic hydrocarbons in water bodies. It is often used in the food industry to determine vitamins, amino acids and other nutrients. It is used in materials science research to analyze the fluorescence properties of semiconductor nanomaterials and organic luminescent materials. It is used in industrial process control to monitor product quality, such as the determination of the content of optical brighteners in textiles. These applications usually refer to relevant test standards issued by international standards organizations or national standardization bodies.
Selection
When selecting instruments, it is necessary to comprehensively consider the technical parameters and usage needs. The spectral range should cover the excitation and emission bands of the substance to be measured. Resolution affects the ability to resolve spectral details, and the adjustable range of slit width is related to the balance of sensitivity and spectral bandwidth. The type of detector, such as a photomultiplier tube or a charge-coupled device, directly affects the detection sensitivity and linearity range. Functional scalability includes support for cryogenic accessories, polarization measurements, or time-resolved fluorescence modules. The data processing capabilities and compliance of the operating software are also considerations. It is recommended to choose based on actual sample characteristics, limit of detection requirements, and budget range.