Application and Precautions of Model 721 Spectrophotometer

721 visible spectrophotometer
"In colorimetric analysis, the depth of the color of the colored substance solution is determined by the intensity of the incident light, the concentration of the colored substance solution and the thickness of the liquid layer. When a beam of monochromatic light irradiates the solution, the stronger the incident light intensity, the greater the concentration of the solution, the thicker the thickness of the liquid layer, and the more the solution absorbs light. The relationship between them conforms to the quantitative law of light absorption by substances. That is the Lambert-Bear law. This is the theoretical basis for the quantitative analysis of substances by spectrophotometry.

The 721 visible spectrophotometer adopts a classic optical system and sophisticated manufacturing technology, which greatly improves the test accuracy and stability of the instrument compared with traditional products; it is widely used in metallurgy, chemical industry, machinery, medicine, biology, agriculture, environmental protection, Teaching and other industries and fields. This instrument is also a necessary inspection equipment for QS in food factories.

principle
Light is an electromagnetic wave with a certain wavelength and frequency. The wavelength range of visible light is 400~760nm, ultraviolet light is 200~400nm, and infrared light is 760~500,000nm. Visible light presents different colors due to different wavelengths, and these wavelengths present different colors within a certain range are called monochromatic light. The white light emitted by the sun or tungsten wire is composite light, which is a mixed light of various monochromatic lights. Using a prism, white light can be divided into various monochromatic lights arranged in order of wavelength, namely red, orange, yellow, green, cyan, blue, purple, etc. This is the spectrum.

Colored substance solution can selectively absorb a part of visible light energy to present different colors, and some colorless substances can characteristically select the energy of ultraviolet light or infrared light. Substances absorb certain wavelengths of light emitted by the light source to form an absorption spectrum. Because the molecular structure of the substance is different, the absorption capacity of light is different, so each substance has a specific absorption spectrum, and under certain conditions, its absorption degree is similar to that The concentration of the substance is proportional, and spectrophotometry is a method of qualitative or quantitative analysis of different substances by using this absorption characteristic of the substance.

721 type spectrophotometer application and precautions

721 type spectrophotometer application and precautions
1 721 How to use the spectrophotometer

1.1 Before turning on the power, the pointer of the electric meter must be at the “0” scale line, otherwise, the correction screw on the electric meter should be adjusted in place.

1.2 Open the lid and power switch of the cuvette chamber, so that the photocell is preheated for more than 15 minutes without light irradiation.

1.3 Rotate the wavelength regulator to select the wavelength of the monochromatic light required for the measurement. To select the appropriate sensitivity, first adjust the sensitivity knob to the middle position, and use the zero adjuster to adjust the meter pointer to the T value of 10%. If it cannot be adjusted, the sensitivity should be increased appropriately.

1.4 Put the blank solution and the solution to be tested, put the blank solution in the light path, cover the cuvette compartment lid, make the photoelectric tube light, and adjust the light quantity adjustment knob to make the meter at the T value of 100%.

1.5 Open the cuvette compartment lid (close the light door), adjust the zero point regulator so that the pointer is at 0% of the T value, then close the lid (open the light door), adjust the light volume adjustment knob so that the pointer is at the T value of 100 % Places. Repeat this adjustment until the pointer is at the T value of 0% and 100% when the light door is closed and when the light door is opened.

1.6 Place the solution to be tested in the light path and close the lid, then the position of the pointer can read the T value or A value of the solution to be tested.

1.7 After the measurement is completed, turn off the switch, remove the power plug, take out the cuvette, wash and dry, and put it away. Cover the dark box of the cuvette and cover the instrument.

2 Precautions for the use of 721 spectrophotometer

2.1 When using a cuvette, only two sides of the frosted glass can be used, and the translucent surface must be wiped dry with lens cleaning paper to protect the translucent surface from damage or stains. Before using the cuvette to fill the solution, it must be rinsed 3 times with the filled solution to avoid changing the concentration of the solution. When the cuvettes are placed in the cuvette, their front and back positions should be as consistent as possible to reduce measurement errors.

2.2 When you need to change the wavelength significantly, after adjusting the T value to 0% and 100%, you should wait a while (because the tungsten filament lamp needs a period of thermal equilibrium time after the brightness changes sharply), and then adjust the T value after the pointer is stable 0% and 100%.

2.3 When the concentration of the tested solution is too large, a neutral filter can be added to the blank solution (the so-called neutral means that their light transmittance in a wide range of wavelengths is basically the same), and its A value is 0.5, There are three types: 1 and 1.5. The so-called A value of 1 is the nominal value, and the actual value is about 1. The actual value must be measured by the instrument used at the actually used wavelength. For example: the actual value of the measured absorber is 0.95, add this absorbance to the blank solution After the film, the reading of the measured solution on the meter is 0.74, then the actual value of the solution is: 0.74+0.95=1.69.

2.4 Choose cuvettes with different optical path lengths according to the content of the solution, so that the A value of the meter reading is between 0.1 and 1, so that a higher accuracy can be obtained.

2.5 In order to ensure the stable operation of the instrument, a stable power supply should be added where the power supply voltage fluctuates greatly. At the same time, the instrument should be well grounded.

2.6 There are two desiccant cartridges at the bottom of the instrument, which should be checked frequently. When the desiccant is found to be invalid, it should be replaced immediately or dried before use. The silica gel in the dark box of the cuvette should also be removed and dried regularly before returning to its original place.

2.7 In order to avoid dust and contamination of the instrument, a cover should be used to cover the instrument when it stops working. After the instrument has been working for several months or after being moved, the accuracy of the wavelength should be checked to ensure the normal use of the instrument and the reliability of the measurement results.

3 The calibration method of 721 spectrophotometer There are many methods of wavelength reading calibration, such as

(1) Interference filters with high wavelength accuracy can be used.

(2) A solution of a colored substance with a known absorption peak (λ) wavelength is used as a standard for calibration. The former method requires special equipment, and its degree is relatively high; the latter method is simple and feasible, and its degree is poor, but for the 721 spectrophotometer, this method has been able to meet the requirements.

Prepare a solution of an appropriate concentration of a substance with a known λ, and use the instrument to be calibrated to measure its A value at different wavelengths within the range of λ ±20nm of the substance. It can start from about 20nm less than the λ of the colored solution and measure every 2nm until the wavelength is greater than about 20nm of the solution λ. For example, use potassium permanganate solution to calibrate, and its λ is 525nm. Therefore, between 505 and 545nm, the absorbance is measured every 2nm. Take the measurement result as an absorption curve, and the obtained curve has an absorption peak (if the curve does not show an absorption peak, it means that the deviation of the wavelength reading of the instrument is greater than 20nm, and the wavelength range of the measurement should be expanded). Set the wavelength of the absorption peak as λ′, Comparing it with the known λ, the difference is the wavelength correction value, expressed as λ correction: λ correction = λ -λ'.

If the wavelength correction value λ is too large, it is necessary to re-adjust the excitation bulb or overhaul the optical system of the monochromator. If the wavelength correction value is less than 10nm, you can use the correction value to correct the wavelength when using the instrument. When λ is calibrated to a positive value, it means that the wavelength reading of the instrument is higher than the true wavelength. Therefore, when using this instrument, if the selected wavelength is λ when measuring a certain solution, then the wavelength reading (λ reading) that should be adjusted is:

Λ reading =λ measuring -λ calibration

For example, use potassium permanganate solution (its λ is 525nm) to calibrate an instrument, and the absorption peak λ′ is measured to be 530nm, then: λ correction=λ -λ′=525nm-530nm=-5nm

When the instrument is used to measure o-phenanthroline iron, the wavelength should be 510nm, and the wavelength reading scale should be rotated to λ Reading: λ reading = λ measurement-λ calibration = 510nm-(-5nm) = 515nm

means that the wavelength reading should be adjusted to 515nm, and the real wavelength at this time is 510nm, which is the λ of o-phenanthroline iron.

4 Summary

721 spectrophotometer is easy to use, low energy consumption, good stability, easy to adjust, relatively high accuracy, relatively wide range of use, so it will still play an important role in the field of analysis and testing.