Clay Brick Making Machine ,Small Clay Brick Making Machine,Manual Clay Brick Making Machine,Clay Brick Making Machine With Dryer Nantong Hengda Non-burned Machinery Engineering Co.,ltd , https://www.hdbrickmachine.com
1 The error caused by the performance of the instrument itself 1.1 The deviation of the polychromatic light contrast with the ear law The precondition for the establishment of the ear law is that the human light is monochromatic light, but the instrument with higher accuracy is even a spectrophotometer with dual monochromators. Only near monochromatic light can be obtained, pure monochromatic light cannot be obtained, it still contains a narrow light pass band, with the property of polychromatic light. The polychromatic light causes a positive or negative deviation from Beer's law. The spectral bandwidth of the fixed slit UV spectrophotometer is generally 1 nm or 2 nm, the adjustable slit can be 0. Inm; visible spectrophotometer bandwidth 6 nm, snm, or even more than a dozen nanometers. The spectral bandwidth should be as small as possible, but as the spectral resolution increases, the sensitivity of the instrument decreases. Therefore, the influence of various conditions must be comprehensively considered when selecting the instrument. When the concentration of the solution is small and the monochromatic light is relatively pure, it can be approximately considered that Beer's law is satisfied.
1.2 Effect of stray light Stray light is the component of other wavelengths outside the spectral bandwidth of the detector to be measured. It is the main source of error in spectral measurements. The causes are: dispersive elements of spectrophotometers, mirrors, lenses, and dust inside the monochromator. At the edge wavelength of the spectrophotometer operating band, due to the monochromator light transmittance, light source radiation intensity, and detector sensitivity are all low, the effect of stray light is more significant. Stray light limitation The upper limit of the instrument's analysis can cause serious measurement errors. In the actual work, in the quantitative analysis, the absorbance of the sample is generally measured at or near the absorption peak. If there is stray light at the analysis wavelength, the sample is transmitted light. The rate is small, and stray light is mostly transmitted, making the measured absorbance lower than the true absorbance.
1.3 Effect of Instrument Noise on Measurement t The instrument noise is also an important indicator of the instrument. It indicates the instrument's ability to make a dilute solution. Is an unwanted signal superimposed on the analysis signal to be measured. Scan the 100% T and 0% T lines to observe the absolute noise level of the spectrophotometer. If the instrument noise is large, it will mask smaller measurement signals. The sensitivity of the instrument is generally expressed as twice the noise.
1.4 Wavelength and Absorbance Accuracy Each sample value is measured at a certain wavelength. If the wavelength error is large, the measured value is certainly not accurate. Absorbance accuracy is also a direct requirement of the user for the instrument, and should be given enough attention. The National Metrology Verification Regulations stipulate that the transmission accuracy of the double-beam UV-Vis spectrophotometer is 0.6% for class A and 1.0% for class B soil.
2 Selection of measurement conditions 2.1 Selection of reference solution and solution The measurement of the spectrophotometer actually measures the absorbance of the sample by using the light intensity of the reference cell as the intensity of the human light, and first adjusts the instrument to make it through the reference cell. The absorbance of the solution is zero, and then the same beam of light passes through the sample, so that the absorbance more truly reflects the concentration of the substance to be measured, so the choice of the reference solution is very important. If only the reaction product of the test substance and the color developing agent has absorption, pure solvent or distilled water may be used as a reference solution. If the coloring agent has a color and absorbs at the measurement wavelength, use the developer solution as a reference solution. The amount of the developer and other reagents added should be the same as the amount added in the sample. If the color of the other components in the sample interferes with the measurement and the color developer used is not colored, the sample solution without the developer is used as the reference solution.
Choosing the right solvent correctly plays an important role in improving the accuracy of the analysis. To reduce the influence of impurities in the solvent, a high-purity solvent should be selected; the solvent should not chemically react with the substance to be detected; the analyte must have a certain degree of solubility in the solvent; the solvent itself is not absorbed within the determined wavelength range. Pay attention to the shortest available wavelength of commonly used solvents. When using volatile solvents, the absorption cell should be capped during the measurement.
2.2 Selection of test wavelength When measuring a solution with a spectrophotometer, it is first necessary to select a suitable measurement wavelength. The choice is based on the absorption curve of the solution being tested. In general, we always choose the maximum absorption wavelength as the measurement wavelength, which can increase the sensitivity. In some cases, the maximum absorption peak is very sharp, the absorption is too large, or there is interference nearby, the maximum absorption wavelength cannot be selected, and it is necessary to select other wavelengths in the absorption curve to determine the sensitivity with certain sensitivity. The corresponding wavelength at the flat) to eliminate interference. Drawing the absorption curve is an effective means and method for correct wavelength selection.
2.3 Selection of absorbance range When the sample absorbs light at different absorbances, the relative error of the concentration is different. Generally, A is selected between 0.2 and 0.8. The relative error of the concentration is small. The thickness of the absorption cell, the detection wavelength, or the concentration of the solution to be tested can be changed. Absorbance readings are within the appropriate range.
2.4 Selection of slit width The slit width not only affects the purity of the spectrum, but also the absorbance value. In the quantitative analysis, a large slit should be used in order to obtain a sufficient measurement signal. In qualitative analysis, smaller slits should be used to obtain finer spectral structures in order to increase the resolution.
2.5 Selection and Use of Absorption Cell The specification of the absorption cell should be determined according to the color depth of the solution to be measured. Generally, when the color of the tested solution is dark, the optical path length is short. When the color is light, the optical path length is long. The same experiment uses the same specification. Set of absorption tanks. Before the quantitative measurement, the absorption cell needs to be calibrated and paired. When the absorption cell does not match, there is an error in the measurement. The direction of the absorption cell is different and the light transmittance is also different. There is an arrow on the upper end of the cuvette glass, which should be consistent with the light path. In addition, do not overfill the solution when using it to prevent the solution from overflowing when the cuvette is being driven. If there is a solution outside the light-transmitting wall, it must be dried and tested again, otherwise it will produce errors.
2.6 Temperature The selected temperature has an effect on the color depth and absorbance of the solution. As the temperature rises, the UV-visible absorption shifts to the short-wave direction. Therefore, when drawing the standard curve and measuring the sample, the temperature should be kept consistent, usually at room temperature.
Since the total measurement error caused by the spectrophotometer comes from the instrument's own performance and measurement conditions, it also comes from various steps of the analysis process, such as sample processing, separation and enrichment, etc., and may cause loss of components to be measured due to chemical operation and The introduction of impurities. Therefore, there are many aspects to analyze when unacceptable measurement errors occur.
The correct use and maintenance of the instrument is also very important, we should do the following: adhere to the standard solution is used now, do not use expired solution; the cell should be kept clean and dry, it is forbidden to touch the transparent surface with a hard object; prevent Instrument vibration, affect the measurement stability; in the boot state, do not measure, you should open the sample cell door to extend the life of the photoelectric sensor; sample concentration measurement to avoid the number of boot, extend the life of the light source; once the shutdown, the lamp should be cooled and then re- Start up and warm up for about 15 minutes; use the desiccant often to prevent the optical components and photoelectric sensors from getting wet and mildew. After the instrument has been moved or replaced with important parts, performance verification must be performed again to ensure accurate measurement results.
Analysis of Measurement Error Sources of Spectrophotometer
Spectrophotometer is a kind of instrument for qualitative or quantitative analysis of substances by selective absorption of light by substances. It has been widely used in various industries and is mainly used for material purity inspection, quantitative analysis, and material structure identification. Measurable results always appear to be acceptable or unacceptable. Errors are due to various aspects of the measurement process. I believe that this is mainly due to the performance of the instrument itself and the choice of measurement conditions.