Fluorescent detector

Features

selective high, only respond to fluorescent substances; high sensitivity, minimum detection limit can reach 10-12 ug / ml, suitable for polycyclic aromatics and various fluorescence Trace analysis of substances. It can also be used to detect substances that can be fluorescence but chemically reactive. As in phenolic analysis, most phenols are not fluorescence, and thus the first treatment causes it to fluorescent substances, followed by analysis.

Detection

The compound is excited by ultraviolet light, emitting light longer than excited light, referred to as fluorescence;

fluorescence intensity (F) The relationship between the excitation light intensity (I0) and the fluorescent substance concentration (c) is: f = 2.3qki0εCl

f = kc

q is quantum yield, k is fluorescent Efficiency, ε is the molar absorbing coefficient, and L is the length of the optical path.

Fluorescence Generate

From the perspective of electronic transition, fluorescence refers to some of the substances absorbed with the same light as its own characteristic frequency, some of the electrons in the atoms from the ground state The minimum vibration level transition to a higher level of vibration levels. Electron strikes in homologous or other molecules, consumes considerable energy, thereby falling to the minimum vibration energy level in the first electron excitation state, and this metastatic form of energy is called a radiation transition. Some of the different levels of different levels fell from the minimum vibration level to the ground state, and simultaneously transmit a low frequency of the original absorption, a light of the wavelength, is fluorescence. The light absorbed by the compound is referred to as excited light, and the resulting fluorescence is referred to as emitting light. The wavelength of fluorescence is always longer than the ultraviolet wavelength of the molecule, usually in the visible range. The properties of fluorescence are closely related to the molecular structure. After the molecules of different structures are excited, they are not emit fluorescence.

Quantification of

In photoluminescence, emitted radiation depends on the amount of radiation absorbed. Since an excited molecule returns to the ground state, energy loss may be generated in the form of no radiation transition, and thus the number of photons emitted radiation is usually less than the number of photons absorbed, it is represented by quantum efficiency Q.

Under fixed experimental conditions, quantum efficiency is a constant, usually Q is less than 1. The Q value is typically between 0.1 to 0.9 for a substance that can be detected by fluorescence. The fluorescence intensity F is proportional to the absorption light intensity. For the dilute solution, the fluorescence intensity is positively correlated with the concentration of the fluorescent material solution, the moisture absorbing coefficient, the absorption pool thicknesses, the incident light intensity, the quantum efficiency of fluorescence, and the color collecting efficiency. Under the conditions that remain unchanged, the fluorescence intensity of the substance is proportional to the concentration of the substance solution, which is the quantitative basis of the fluorescence detector. The fluorescent detector belongs to a solute detector that can be used directly in quantitative analysis.

type

Fluorescence involves two absorption and emission of light, so any fluorescent compound has two characteristics: excitation spectrum and emission spectrum (EMISITION) Spectrum).

excitation spectrum

fluorescence belongs to photoluminescence, and the appropriate excitation light wavelength (EX) is required to facilitate detection. The excitation wavelength can be determined by the excitation spectrum of the fluorescent compound. The specific detection method of excitation spectroscopy is to excite the monochrome by scanning the monochrome, which causes the fluorescent compound of the incident light of different wavelengths, and the resulting fluorescence is detected by the light detecting element by the emission monochrometer of the fixed wavelength. The relationship between the fluorescence intensity to the excitation wavelength is excited spectrum. At the maximum wavelength of the excitation spectrum curve, the number of molecules in the excited state is most, that is, the absorbed light energy is also the most, and the strongest fluorescence can be produced. When considering sensitivity, the measurement should select the maximum excitation wavelength.

Emission spectrum

Generally, the fluorescence spectrum is actually referred to as a fluorescence emission spectrum. It is a curve of the fluorescence intensity obtained by the wavelength scan of the wavelength (ie, emission wavelength, EM). Fluorescence spectroscopy can be used to identify fluorescent substances and as a basis for selecting a suitable measurement wavelength as fluorescence assay.

Additionally, due to the characteristics of the fluorescence measuring instrument, the energy distribution of the light source, the transmittance of the mononer, and the response of the detector can be changed as the wavelength, so the same compound will be on different instruments. Different spectrograms are obtained, and there is no compalability between each other. This spectrum is called a table viewing spectrum. To allow the same compound to obtain a fluorescence spectrum having the same characteristics on a different instrument, the above characteristics of the instrument are required to correct. The corrected spectroscopy is called a true fluorescence spectrum.

The excitation wavelength and the emission wavelength are the necessary parameters of fluorescence detection. Choosing a suitable excitation wavelength and emission wavelength, it is important to improve the sensitivity and selectivity of the test, especially to a large extent improve detection sensitivity.