How to Calibrate the Wavelength Error of Colorimeter?

The colorimeter is a commonly used analyzer in laboratories and laboratories at all levels. It is most popular among analysts at all levels because of its low price, simple operation, convenient use, a wide range of use, and high accuracy and precision. The sensitivity is related to the characteristics of the instrument – the luminous intensity of the light source lamp, the resolution of the monochromator, and the spectral sensitivity of the photoelectric conversion element. The wavelength is corrected, but after long-distance fishing and back-and-forth during use, the shape and movement of the speaker and other factors will cause the speaker to produce wavelength differences of different sizes. For this reason, the manufacturer is equipped with a wrong filter or interference filter to correct the wavelength in the elbow of the instrument so that the user can adjust the calibration regularly. Under normal circumstances, the newly purchased instrument needs to be calibrated once and then calibrated once for each pain-specified limit according to the usage. However, this common sense is ignored by most operators and even discards the anchor filter and never performs wavelength calibration on the instrument. In this way, for instruments with a large wavelength difference, the improvement of the sensitivity and accuracy of the star measurement will inevitably be affected, and the reliability of the star measurement results will be reduced.

There are many methods for correcting the wavelength. The praseodymium neodymium filter method and the standard reagent method are introduced as follows:

Correction and principle with praseodymium neodymium filter

The praseodymium neodymium filter in the instrument box is a kind of glass material that contains rare metals. The absorption spectrum of rare metals is generated by the transition of inner electrons, the peak-shaped symmetrical half-width is narrow and the maximum absorption is obvious due to the shielding effect of the outer electrons. In order to reduce the reading error, the manufacturer Yiyi recommends using the absorption peak of 52 nm as the calibration standard among its several absorption peaks. Therefore, the user can put the anchor filter on the filter holder in the property and put it in the colorimetric chamber to measure it every 2m, measure it every t1m at the maximum absorption and attack peak, and record the measurement at the corresponding wavelength. Finally, take the wavelength as the abscissa and the absorbance as the ordinate, and draw the absorption spectrum curve (as shown in the figure).

The absorption spectrum curve

It can be seen from the figure that there is an absorption peak with suitable absorbance at 528mm. If the absorption peak deviates from 521nm, it indicates that the instrument has a wavelength difference, and the allowable clock wavelength difference is ±3m. If it exceeds this value, it should be corrected. For ATO-CM-NR110 or ATO-CM-SC-10, it can be corrected by moving the wavelength disc. If the absorption peak is less than 52nm, the wavelength correction can be adjusted clockwise. When the burst wire is greater than 521m, the wavelength adjustment screw can be turned counterclockwise. To play, you only need to move the gauge each time, and then test it again until you reach the point of the shot.

The standard reagent method

In the absence of praseodymium and neodymium filters, the wavelength can be corrected according to the following standard solutions. which is:

Calibrate the wavelength

The maximum absorption wavelength of the absorption spectrum of these substances is unchanged, only the absorbance is different, especially the chlorides of some rare earth elements. Not only is the maximum absorption wavelength is fixed, but also the absorption peak is narrow, which is more conducive to the wavelength correction, the correction method is the same as before.

The measurement result is that, if it is not corrected, it will inevitably affect the measurement accuracy of the photometer, especially the measurement of the narrow-band absorption of the measured sample. The wavelength is selected according to the data provided in the technical data, not only deviating from the maximum absorption wavelength but even the selected possible wavelength. is the minimum absorption wavelength, then the accuracy of the measurement results is very unreliable, and even erroneous conclusions can be drawn.

In the process of using the colorimeter, due to mechanical vibration, temperature change, deformation of the filament, loose lamp holder, or replacement of the bulb, the reason often causes the error between the reading of the wavelength on the dial and the wavelength actually passed through the solution, which reduces the sensitivity of the instrument and affects the scale result. accuracy, and even draw erroneous conclusions. Therefore, each operator should strengthen the maintenance of the instrument, understand the characteristics of the instrument, master the calibration method of the instrument, calibrate the instrument regularly, and use the instrument reasonably to make the measurement results more accurate.

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