Ask about the principle of spectrophotometry and the application of spectrophotometry

Spectrophotometry.

Spectrophotometry is a method of qualitative and quantitative analysis of a substance by measuring the absorbance or luminous intensity of light at a specific wavelength or within a certain wavelength range.

In a spectrophotometer, when different wavelengths of light are continuously irradiated to a certain concentration of sample solution, the absorption intensity corresponding to the different wavelengths can be obtained. If the wavelength ( ) is used as the abscissa and the absorption intensity (a) is used as the ordinate, the absorption spectrum curve of the substance can be plotted. The qualitative and quantitative analysis method of substances using this curve is called spectrophotometry, also known as absorption spectroscopy.

The method of determining colorless substances with an ultraviolet light source is called ultraviolet spectrophotometry; The method of determining colored substances with a visible light source is called visible photometry. They, like colorimetry, are based on Beer-Lambert's law.

The ultraviolet and visible regions mentioned above are commonly used. However, the application of spectrophotometry includes ultraviolet light region, visible light region, and infrared light region.

Wavelength range. 1) 200 400nm ultraviolet region, (2) 400 760nm visible region, 3) 4000cm<-1> 400cm<-1>) infrared region by wavenumber.

Instrument. Ultraviolet spectrophotometer, visible spectrophotometer (or colorimeter), infrared spectrophotometer, or atomic absorption spectrophotometer. In order to ensure the precision and accuracy of the measurement, all instruments should be calibrated regularly in accordance with the national metrology verification regulations or the provisions of this appendix.

The rationale for this paragraph.

When a beam of monochromatic light with intensity i0 irradiates the solution of a substance perpendicularly, because a part of the light is absorbed by the system, the intensity of the transmitted light decreases to i, and the transmittance t of the solution is:

According to the Lambert-Beer law:

A=ABC where A is the absorbance, B is the thickness of the solution layer (cm), C is the concentration of the solution (G DM3), and A is the absorbance coefficient. where the absorbance coefficient.

It is related to factors such as the nature of the solution, temperature, and wavelength. The absorption of light by other components in the solution (e.g., solvents, etc.) can be deducted by the blank solution.

From the above equation, it can be seen that when the thickness of the solution layer l and the absorbance coefficient a are fixed, the absorbance a is linearly related to the concentration of the solution. For quantitative analysis, the absorption of light at different wavelengths by the solution (absorption spectrum) is first determined to determine the maximum absorption wavelength.

And then at this wavelength.

The absorbance of a series of known concentrations of C solutions was determined to make a C working curve. When analyzing an unknown solution, the corresponding concentration can be determined by checking the working curve according to the measured absorbance a. This is the basic principle of spectrophotometric concentration measurement.

Reference Encyclopedia).

Spectrophotometry: qualitative and quantitative analysis of substances.

The application of spectrophotometry has a wide range of applications in the qualitative analysis of organic matter, and in the field of inorganic matter, it is used in the study of minerals, semiconductors, natural products and compounds.

Spectrophotometry is a method of qualitative and quantitative analysis of a substance by measuring the absorbance or luminous intensity of light at a specific wavelength or within a certain wavelength range.

Spectrophotometry features: Substances can be identified by comparing the spectra of a sample in a specific wavelength range with a control spectrum or a reference spectrum, or by determining the maximum absorption wavelength, or by measuring the absorption ratio at two specific wavelengths.

For quantification, the absorbance of a sample solution of a certain concentration is measured at the maximum absorption wavelength, and the absorbance of a certain concentration of the control solution is compared with that of a control solution of a certain concentration or the concentration of the sample solution is calculated by the absorption coefficient method.

Applications include:

Quantitative analysis, widely used in the determination of trace, ultra-micro and constant inorganic and organic substances in various materials.

For qualitative and structural analysis, UV absorption spectroscopy can also be used to infer spatial hindrance effects, hydrogen bond strength, tautomerism, geometric isomerism, etc.

Reaction kinetics study, that is, to study the functional relationship of reactant concentration with time, to determine the reaction speed and reaction order, and to study the reaction mechanism.

Study of solution equilibrium, such as determination of complex composition, stability constant, acid-base dissociation constant, etc.

The basic principle of spectrophotometry is Lambert-Beer's law.

Spectrophotometry: The solution of many substances has color, and the color exhibited by colored solutions is due to the selective absorption of light by the substances in the solution. Different substances have different absorption spectra due to their different molecular structures and different absorption capacities for different wavelengths of light.

Even the same substance absorbs light differently due to its different contents. A method of identifying a substance by using the absorption spectrum unique to a substance, or determining the content of a substance by using the degree of absorption of a certain wavelength of light by a substance.

The significance of Lambert-Beer's law is that when a beam of monochromatic light passes through a homogeneous solution, the degree of absorption of the monochromatic light trail by the solution is proportional to the product of the concentration of the solution and the thickness of the liquid layer.

Matter interacts with light and has the property of selective absorption. The color of a colored substance is produced by the interaction of the substance with light. That is, the color exhibited by a colored solution is due to the selective absorption of light by the substances in the solution.

Due to the different molecular structures of different substances, the absorption capacity of different wavelengths of light is also different, so the structural group with characteristic structure has the maximum received wavelength to select the absorption characteristics, form the maximum absorption peak, and produce a unique absorption spectrum. Even the same substance has different degrees of absorption of light due to its different contents.

Spectrophotometry is a method of identifying the presence of a substance using the absorption spectrum unique to a substance (qualitative analysis), or a method of determining the content of a substance by carefully using the absorption of light of a certain wavelength by a substance (quantitative analysis).

Testing instruments

Instrument classification. According to the spectral region, spectrophotometers can be divided into: ultraviolet spectrophotometer, visible spectrophotometer (or colorimeter), infrared spectrophotometer. If the absorbance particle is an atom, its instrument is called an atomic absorption spectrophotometer.

Instrument composition. The basic components of various spectrophotometers are: light source system, spectroscopic system, absorption system and detection system.

The principle of the spectrophotometer is that different substances have their own absorption bands based on the selectivity of the absorption of light (the wavelength of light).

A spectrophotometer, also known as a spectrometer, is a scientific instrument that decomposes light with complex composition into spectral lines. The measurement range generally includes the visible region with a wavelength range of 380 780 nm and the ultraviolet region with a wavelength range of 200 380 nm. Different light sources have their own unique emission spectra, so different luminaires can be used as the light source of the instrument.

Emission spectrum of tungsten lamp: the spectral light with a wavelength of 380 780nm emitted by the tungsten lamp source is refracted by a prism to obtain a continuous chromatogram composed of red, orange, yellow, green, blue, indigo and violet. This chromatography can be used as a light source for visible spectrophotometers.

The concept of a spectrophotometer

The beam sent to the sample is made up of photon beams. When photons encounter molecules in a sample, the molecules can absorb some of them, reducing the number of photons in the beam and reducing the intensity of the detection signal. Transmittance is the part of the light that passes through the sample.

It is defined as the intensity of light passing through a sample at the intensity of incident light.

Absorbance is the opposite of transmittance and corresponds to the amount measured by a spectrophotometer. Based on the absorbance, the concentration in the solution sample can be determined from Bill Lambert's law, which indicates that there is a sexual relationship between absorbance and sample concentration. According to Beer-Lambert's law, absorbance is the product of the absorption coefficient, which is a measure of the amount of light absorbed by the solute at a given wavelength, which is the distance the light travels.

Potato lead sample, or distance traveled, and the concentration of the solute. Typically, the goal of measuring absorbance is to measure the concentration of the sample.

The above content refers to Encyclopedia - Spectrophotometer.

The principle of spectrophotometer is to use a light source that can produce multiple wavelengths, through a series of spectrophotometers, so as to produce a specific wavelength of light source, after the light passes through the test sample, part of the light is absorbed, calculate the absorbance value of the sample, and then convert it into the concentration of the sample.

The wavelength of selective absorption of light by a substance, as well as the corresponding absorption coefficient, are the physical constants of the substance. When the absorption coefficient of a pure substance under certain conditions is known, the test sample can be prepared into a solution under the same conditions, and its absorption degree can be determined, and the content of the substance in the test sample can be calculated from the above formula.

In the visible light region, in addition to some substances that absorb light, many substances themselves do not absorb but can be determined after adding chromogenic reagents or processing them under certain conditions, so it is also called colorimetric analysis. Because there are many factors that affect the color depth during color development, and instruments with poor purity of monochromatic light are often used, the standard lead and reed standard or reference substance should be used for the determination at the same time.