Performance inspection of the hottest spectrophoto

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Performance inspection of spectrophotometer

(1) wavelength correction: when using photoelectric colorimeter or spectrophotometer, wavelength correction should be carried out after replacing light source lamp, reinstallation, handling or maintenance, and when the instrument is not working normally. Even for instruments that work normally, the wavelength should also be checked every other month, and calibrated if necessary. We can help reduce the harm of plastic waste to the environment, so as to ensure that the wavelength reading is consistent with the wavelength passing through the sample and ensure the maximum sensitivity of the instrument. Methods the spectral neodymium filter correction method is commonly used, which is suitable for the wavelength correction of the visible light region of the 721 instrument. The absorption peak or T% at 585nm or 529nm is often used as the standard. In view of the wide wavelength of the emitted light of the 721 instrument, it is not easy to separate the two peaks or valleys of 573Nm and 585nm, and it is easy to produce errors during correction, so it is recommended to use the peak or valley at 529nm as the standard for wavelength correction. During calibration, preheat the instrument as required. The power supply voltage is required to be stable. Set the wave length dial at 580nm, adjust t% to the maximum, put a white paper strip at the cuvette, and observe whether there is a spot with uniform light intensity and no halo or stray light at the edge. If it does not meet the requirements, adjust the bulb position to meet the requirements, which is a rough adjustment for wavelength correction. Then turn the sensitivity to 1 (the lowest gear), align the wave length disc with 529nm, set the mechanical zero point of the meter to zero, adjust t% to 100% T when the optical path is blank, and check the stability of the zero point and 100% t repeatedly. Insert the spectral neodymium filter into the optical path, slowly rotate the wave length disk, and find the point with the lowest transmittance (when rotating the wave length disk to the left and right, the transmittance value of this point increases), which is the wavelength of 529nm. Check whether the indicated value of the wave length disc is 529nm. If the indicated value is 534nm, the wavelength error is 5nm at this time. If it exceeds the specified value (1nm), it must be adjusted

adjustment method: aim the wave length disc at 529nm, take out the spectral neodymium filter from the optical path, adjust the meter pointer to 100% T when the optical path is blank, and then insert the spectral neodymium filter into the optical path. Open the small cover plate on the left side of the instrument and find the wavelength correction screw (one with the long left handle among the three); Slightly adjust in the counterclockwise direction (clockwise in case of negative error) to minimize the indication T% of the meter pointer. Check the wavelength error repeatedly. When the resistance value of the friction contact area R << R1, until it meets the technical indicators of the instrument. Cover the left small cover plate, and the correction is over

some high-end instruments, such as Shimadzu UV-260 dual beam spectrophotometer, can use a hydrogen lamp or place a spectral neodymium filter in the determination colorimetric tank, and after being programmed into the filter scanning program, the instrument can automatically correct the wavelength within a certain wavelength range. The optical system of the high-end spectrophotometer is sealed in a unit assembly. In case of failure and inaccurate wavelength, the manufacturer must often send someone to repair it. Other methods include spectral line correction, interference filter correction and colored solution correction. Please refer to relevant materials

(2) linearity check: linearity check includes two aspects: instrument linearity and measurement method linearity. The linear error shows that the concentration of the solution does not have a linear relationship with the absorbance, and there is a positive deviation or negative deviation. This deviation, according to beer's law, comes from two aspects: first, the solution itself does not conform to beer's law, which is called chemical deviation; Second, the influence of various factors of the instrument itself makes the measured value of absorbance not linear with the concentration. This phenomenon is called instrument deviation. The latter is studied here. There are many factors for the deviation of the instrument, such as stray light, limited bandwidth, detector noise, changes in environmental conditions, changes in wavelength, cuvette error, non parallelism of radiated light, nonlinearity of the detector itself, etc

instrument linearity check usually uses a colored substance that is sure to be coated with a layer of grease on the surface of the sample in a certain wavelength and a certain concentration range to prevent rust. It obeys beer's law and is prepared into a solution of different concentrations to check whether the instrument itself can truthfully reflect the concentration change of colored substances. This inspection method has nothing to do with any methodological problems such as the color reaction of the tested substance. Using the measured absorbance to plot the concentration should be a straight line under ideal conditions. The commonly used method is to use the concentration series of 0.8, 1.6, 2.4, 4.0mg/l Evan blue to check, and the wavelength is 610nm

(3) stray light (astigmatism) inspection: in absorbance measurement, all unwanted radiation felt by the detector is called stray light. Stray light has a serious impact on the accuracy of absorbance, but it is often ignored. The sources of stray light include: ① the reasons of the instrument itself, such as the design of monochromator, the spectral distribution of light source, the aging degree of optical elements, the width of wave band, and the reflection and scattering inside the instrument; ② The indoor light is too strong and leaks into the instrument, and the dark room of the instrument is not tightly covered; ③ The reason of the sample itself, such as whether the sample has fluorescence, the scattering ability of the sample, etc

stray light detection method: ① stray light monitoring in the ultraviolet light area can use 100.1g/l sodium iodide solution, and the absorbance measured at 240nm should be greater than 2.00. In addition, the light transmittance of 12g/l potassium chloride solution can also be measured at 220nm, that is, the amount of stray light, which should generally be less than 1% t. All the above measurements are made with quartz cup and calibrated with distilled water. ② In the visible light region, the spectral neodymium filter or nickel sulfate method can be used for inspection. First, use the spectral neodymium filter to correct the wavelength, then block the optical path of the cuvette with black paper (the imported instrument has a cuvette sample black standard column), then adjust 0% T, and then use air to adjust 100% t. Insert a spectral neodymium filter and measure it at 585nm. The measured value is the stray light level

(4) quality inspection of cuvette: cuvettes are generally made of glass, quartz or fluorspar, with a light path of 1.0 or 0.5cm. When light passes through, some light is lost (4%) due to the reflection of the contact surface between air and glass, and the other part (rarely) is absorbed by glass. Jinan experimental machine factory will introduce in detail 1 wedge load test and its distinction from tensile test. In addition to its raw materials, the quality of the cuvette is that the thickness of the glass is uniform, consistent from top to bottom, and the cups match each other. The manufacturer usually supplies it in four sets, and the outside of the upper part of the cup mouth is marked with an arrow, which is used on the side of the light source. Nevertheless, quality inspection should be carried out before use. Common Evan blue method: inject a certain amount of 2.0mg/l Evan blue solution into the cuvette, and the liquid level in the cuvette should be equal. Use a cuvette as the standard, use a red filter (wavelength 600 ~ 610nm), calibrate with water, and then accurately adjust the reading of this cuvette to 50% T, and then read the light transmittance of other cuvettes. It is qualified if the light transmittance difference is within 0.5% t

(5) stability check: check method: connect the spectrophotometer and accessories to an adjustable transformer above 0.5kva, first adjust the voltage to 220V, fix the wavelength at 650nm, fill the optical path cuvette with blank solution, adjust the reading to 90% T, then increase the voltage to 230V and reduce it to 190V, and observe the drift value of the transparency. It is qualified if it is between 88.5% and 91.5% t. Under the condition of constant power supply voltage, the reading drift shall not exceed 0.5% of the upper limit of the scale within 3 minutes

(6) repeatability check: repeat the check on the premise that the wavelength, working state, power supply voltage, matching of cuvette, etc. are qualified. When using AC power supply, the reading difference of the instrument for repeated determination of a solution should be less than or equal to 1% of the upper limit of the scale. Test method: dry the analytical pure potassium bicarbonate at 120 ~ 150 ℃ for 2 hours, and then cool it in the dryer. Weigh 509.1mg in a 1000ml volumetric flask, dissolve it in distilled water, add it to the scale, and mix it evenly (180mg/l chromium). The use solution is 30, 60, 180mg chromium/l. Take the wavelength of 440nm, measure each concentration tube of the application solution for 3 ~ 5 times continuously, and it is qualified if the maximum error in each concentration tube is less than 1% t

(7) sensitivity test: prepare potassium dichromate solution into four application solutions of 30 and 32.5mg chromium/l and 120 and 122.5mg/l chromium (the concentration difference between the two groups is 2.5mg/l chromium respectively). The wavelength is 440nm, and the absorbance of the above application solution is measured continuously for three times with water calibration zero point. It is qualified if the absorbance value difference of the two groups of 2.5mg/l chromium concentration difference is not less than 0.01

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