Spectrophotometry is the qualitative and quantitative analysis of the substance by measuring the absorbance of light at a specific wavelength or a certain wavelength range. Commonly used wavelength ranges are: (1) ultraviolet light region of 200 to 400 nm (2) visible light region of 400 to 760 nm, (3) 2.5 to 25 μm (4000 cm <-1> to 400 cm <-1> by wave number) Infrared zone.
The instrument used is an ultraviolet spectrophotometer, a visible spectrophotometer (or colorimeter), an infrared spectrophotometer or an atomic absorption spectrophotometer. In order to ensure the precision and accuracy of the measurement, all instruments shall be regularly calibrated according to the national metrological verification regulations or the provisions of this appendix.
Spectrophotometers are precision optics, and proper installation, use, and maintenance are important to maintain good instrument performance and to ensure test accuracy.
(1) Requirements for the working environment of the instrument
The requirements of the spectrophotometer for the working environment are as follows:
1 The instrument should be placed in a dry room at a temperature of 5 to 35 ° C. The relative humidity does not exceed 85%.
2 The instrument should be placed on a firm and stable work surface and avoid strong vibration or continuous vibration.
3 indoor lighting should not be too strong, and should avoid direct sunlight.
4 The electric fan should not be directly blown to the instrument to prevent the light source lamp from affecting the normal use of the instrument due to unstable illumination.
5 Try to stay away from high-intensity magnetic fields, electric fields, and electrical equipment that generate high-frequency waves.
6 The power supply voltage supplied to the instrument is AC220V±22V, the frequency is 50Hz±1Hz, and a good grounding wire must be installed. It is recommended to use an electronic AC voltage regulator with an electric power of 1000w or more or an AC constant voltage regulator to enhance the anti-jamming performance of the instrument.
7 Avoid use in places where corrosive gases such as hydrogen sulfide are present.
(2) Daily maintenance and maintenance of the instrument
1 light source. The life of the light source is limited. In order to prolong the service life of the light source, do not turn on the light source when the instrument is not in use. The number of switching should be minimized. The lights may not be turned off during short working intervals. The light source that has just been turned off cannot be turned back on immediately.
The continuous use of the instrument should not exceed 3 hours. If you need to use it for a long time, it is best to pause for 30 minutes.
If the brightness of the light source lamp is significantly weakened or unstable, the new lamp should be replaced in time. After the replacement, adjust the position of the filament. Do not touch the window or the bulb directly with your hands to avoid oil stains. If you have accidentally touched it, wipe it with absolute ethanol.
2 monochromators. The monochromator is the core part of the instrument and is housed in a sealed box and cannot be disassembled. The selected wavelength should be rotated in a balanced manner, and the unavailability is too strong. In order to prevent the dispersive elements from being exposed to moisture, the monochromator desiccant (silica gel) must be replaced periodically. If the desiccant is found to be discolored, it should be replaced immediately.
3 absorption pool. The absorption cell must be used correctly and special care should be taken to protect the two optical faces of the absorption cell.
4 detectors. The photoelectric conversion element cannot be exposed for a long time, and strong light irradiation or moisture accumulation should be avoided.
5 When the instrument stops working, the power must be turned off.
6 In order to avoid dust and contamination of the instrument, the dust cover should be covered when the work is stopped.
7 If the instrument does not need to be energized regularly, it should be no less than 20~30min each time to keep the whole machine dry and maintain the performance of electronic components.
UV-visible spectrophotometer type
UV-visible spectrophotometer can be divided into two categories according to the wavelength range: visible spectrophotometer and ultraviolet-visible spectrophotometer. The former uses a wavelength range of 400 to 780 nm; the latter uses a wavelength range of 200 to 1000 nm.
According to the optical path ultraviolet-visible spectrophotometer, it can be divided into two types: single beam type and double beam type; the number of wavelengths provided by measurement can be divided into two types: single wavelength spectrophotometer and dual wavelength spectrophotometer.
The so-called single beam refers to the light emitted from the light source. After passing through a series of optical components such as a monochromator and the absorption cell, it is always a beam of light when it is finally illuminated on the detector. Commonly used single-beam UV-visible spectrophotometers are 751G, 752, 754
Type, 756MC type, etc. Commonly used single-beam visible spectrophotometers are 721, 722, 723, 724, etc.
The single-beam spectrophotometer is characterized by its simple structure and low price, and is mainly suitable for quantitative analysis. The shortcoming is that the measurement result is greatly affected by the fluctuation of the intensity of the light source, thus bringing a large error to the quantitative analysis result.
A two-beam spectrophotometer means that light emitted from a light source passes through a monochromator and is split into two beams of equal intensity by a rotating sector mirror (ie, a cutter), passing through a reference solution and a sample solution, respectively. Using another dimmer synchronized with the previous dimmer, the two beams are alternately illuminated on the same detector at different times, and the signals from the two beams are compared by a sync signal generator and The ratio of the two signals is converted to the corresponding absorbance value after logarithmic transformation.
Commonly used dual-beam UV-visible spectrophotometers are 710, 730, 760MC, 760CRT, and Shimadzu UV-210. The characteristics of this type of instrument are: continuous change of wavelength, automatic comparison of the light transmission intensity of the sample and the reference solution, and automatic elimination of errors caused by changes in the intensity of the light source. Such instruments are extremely suitable for the analysis of complex absorption spectrum curves that must be obtained over a wide range of wavelengths.
The main difference between the dual-wavelength spectrophotometer and the single-wavelength spectrophotometer is that a dual monochromator is used to simultaneously obtain two monochromatic lights of different wavelengths. The light from the light source is split into two beams, which are respectively passed through two freely rotatable grating monochromators to obtain two monochromatic lights having different wavelengths A1 and A2. By means of the light cutter, the two beams are alternately irradiated to the absorption cell containing the test solution at a certain time interval, and the difference between the transmittance Δr or the absorbance difference of the test solution at the wavelengths λ1 and λ2 is displayed by the detector. A, then
△A=Aλ1-Aλ2=(Eλ1-Eλ2)bc
It can be seen from the formula that ΔA is proportional to the light absorbing substance c. This is the theoretical basis for quantitative analysis of dual-wavelength spectrophotometry.
Commonly used dual-beam spectrophotometers are domestic wFZ800S, Japan Shimadzu UV-300, UV-365 and so on.
The characteristics of this type of instrument are: no reference solution, only one solution to be tested, so the background absorption interference can be eliminated, including the difference between the composition of the solution to be tested and the reference solution and the difference in the thickness of the absorption liquid, which improves the measurement. Accuracy. It is especially suitable for quantitative analysis of mixtures and turbid samples, and can be used for derivative spectrum analysis. The downside is that it is expensive.
The instrument used is an ultraviolet spectrophotometer, a visible spectrophotometer (or colorimeter), an infrared spectrophotometer or an atomic absorption spectrophotometer. In order to ensure the precision and accuracy of the measurement, all instruments shall be regularly calibrated according to the national metrological verification regulations or the provisions of this appendix.
Spectrophotometers are precision optics, and proper installation, use, and maintenance are important to maintain good instrument performance and to ensure test accuracy.
(1) Requirements for the working environment of the instrument
The requirements of the spectrophotometer for the working environment are as follows:
1 The instrument should be placed in a dry room at a temperature of 5 to 35 ° C. The relative humidity does not exceed 85%.
2 The instrument should be placed on a firm and stable work surface and avoid strong vibration or continuous vibration.
3 indoor lighting should not be too strong, and should avoid direct sunlight.
4 The electric fan should not be directly blown to the instrument to prevent the light source lamp from affecting the normal use of the instrument due to unstable illumination.
5 Try to stay away from high-intensity magnetic fields, electric fields, and electrical equipment that generate high-frequency waves.
6 The power supply voltage supplied to the instrument is AC220V±22V, the frequency is 50Hz±1Hz, and a good grounding wire must be installed. It is recommended to use an electronic AC voltage regulator with an electric power of 1000w or more or an AC constant voltage regulator to enhance the anti-jamming performance of the instrument.
7 Avoid use in places where corrosive gases such as hydrogen sulfide are present.
(2) Daily maintenance and maintenance of the instrument
1 light source. The life of the light source is limited. In order to prolong the service life of the light source, do not turn on the light source when the instrument is not in use. The number of switching should be minimized. The lights may not be turned off during short working intervals. The light source that has just been turned off cannot be turned back on immediately.
The continuous use of the instrument should not exceed 3 hours. If you need to use it for a long time, it is best to pause for 30 minutes.
If the brightness of the light source lamp is significantly weakened or unstable, the new lamp should be replaced in time. After the replacement, adjust the position of the filament. Do not touch the window or the bulb directly with your hands to avoid oil stains. If you have accidentally touched it, wipe it with absolute ethanol.
2 monochromators. The monochromator is the core part of the instrument and is housed in a sealed box and cannot be disassembled. The selected wavelength should be rotated in a balanced manner, and the unavailability is too strong. In order to prevent the dispersive elements from being exposed to moisture, the monochromator desiccant (silica gel) must be replaced periodically. If the desiccant is found to be discolored, it should be replaced immediately.
3 absorption pool. The absorption cell must be used correctly and special care should be taken to protect the two optical faces of the absorption cell.
4 detectors. The photoelectric conversion element cannot be exposed for a long time, and strong light irradiation or moisture accumulation should be avoided.
5 When the instrument stops working, the power must be turned off.
6 In order to avoid dust and contamination of the instrument, the dust cover should be covered when the work is stopped.
7 If the instrument does not need to be energized regularly, it should be no less than 20~30min each time to keep the whole machine dry and maintain the performance of electronic components.
UV-visible spectrophotometer type
UV-visible spectrophotometer can be divided into two categories according to the wavelength range: visible spectrophotometer and ultraviolet-visible spectrophotometer. The former uses a wavelength range of 400 to 780 nm; the latter uses a wavelength range of 200 to 1000 nm.
According to the optical path ultraviolet-visible spectrophotometer, it can be divided into two types: single beam type and double beam type; the number of wavelengths provided by measurement can be divided into two types: single wavelength spectrophotometer and dual wavelength spectrophotometer.
The so-called single beam refers to the light emitted from the light source. After passing through a series of optical components such as a monochromator and the absorption cell, it is always a beam of light when it is finally illuminated on the detector. Commonly used single-beam UV-visible spectrophotometers are 751G, 752, 754
Type, 756MC type, etc. Commonly used single-beam visible spectrophotometers are 721, 722, 723, 724, etc.
The single-beam spectrophotometer is characterized by its simple structure and low price, and is mainly suitable for quantitative analysis. The shortcoming is that the measurement result is greatly affected by the fluctuation of the intensity of the light source, thus bringing a large error to the quantitative analysis result.
A two-beam spectrophotometer means that light emitted from a light source passes through a monochromator and is split into two beams of equal intensity by a rotating sector mirror (ie, a cutter), passing through a reference solution and a sample solution, respectively. Using another dimmer synchronized with the previous dimmer, the two beams are alternately illuminated on the same detector at different times, and the signals from the two beams are compared by a sync signal generator and The ratio of the two signals is converted to the corresponding absorbance value after logarithmic transformation.
Commonly used dual-beam UV-visible spectrophotometers are 710, 730, 760MC, 760CRT, and Shimadzu UV-210. The characteristics of this type of instrument are: continuous change of wavelength, automatic comparison of the light transmission intensity of the sample and the reference solution, and automatic elimination of errors caused by changes in the intensity of the light source. Such instruments are extremely suitable for the analysis of complex absorption spectrum curves that must be obtained over a wide range of wavelengths.
The main difference between the dual-wavelength spectrophotometer and the single-wavelength spectrophotometer is that a dual monochromator is used to simultaneously obtain two monochromatic lights of different wavelengths. The light from the light source is split into two beams, which are respectively passed through two freely rotatable grating monochromators to obtain two monochromatic lights having different wavelengths A1 and A2. By means of the light cutter, the two beams are alternately irradiated to the absorption cell containing the test solution at a certain time interval, and the difference between the transmittance Δr or the absorbance difference of the test solution at the wavelengths λ1 and λ2 is displayed by the detector. A, then
△A=Aλ1-Aλ2=(Eλ1-Eλ2)bc
It can be seen from the formula that ΔA is proportional to the light absorbing substance c. This is the theoretical basis for quantitative analysis of dual-wavelength spectrophotometry.
Commonly used dual-beam spectrophotometers are domestic wFZ800S, Japan Shimadzu UV-300, UV-365 and so on.
The characteristics of this type of instrument are: no reference solution, only one solution to be tested, so the background absorption interference can be eliminated, including the difference between the composition of the solution to be tested and the reference solution and the difference in the thickness of the absorption liquid, which improves the measurement. Accuracy. It is especially suitable for quantitative analysis of mixtures and turbid samples, and can be used for derivative spectrum analysis. The downside is that it is expensive.
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