Selection of Measuring Conditions for Ultraviolet-Visible Spectrophotometer

Release time：2019-03-19

Selection of Measuring Conditions for Ultraviolet-Visible Spectrophotometer

1. Selection of reference solutions and solvents

Ultraviolet-visible spectrophotometer actually measures the absorbance of the sample by using the light intensity of the reference cell as the human light intensity. First, adjust the instrument to make the absorbance of the solution through the reference cell zero, then let the same beam of light pass through the sample, so that the absorbance truly reflects the concentration of the substance to be measured, so the choice of the reference solution is very important.

Pure solvents or distilled water can be used as reference solutions if only the reaction products of the substance to be measured and the chromogenic agent are absorbed. If the chromogenic reagent has color and is absorbed at the determined wavelength, the chromogenic reagent solution is used as the reference solution. The amount of the human chromogenic reagent and other reagents added should be the same as the amount added in the sample.

If the color of other components in the sample itself interferes with the determination, and the color developer used is colorless, the sample solution without the color developer is used as the reference solution.

Correct selection of suitable solvents plays an important role in improving the accuracy of analysis. In order to reduce the influence of impurities in solvents, high purity solvents should be selected; solvents should not react with the substances to be measured; the substances to be measured should have a certain solubility in the solvent; in the range of measured wavelength, the solvent itself does not absorb, pay attention to the shortest available wavelength of commonly used solvents; when using volatile solvents, the absorption cell should be covered in the measurement process.




2. Selection of Test Wavelength

When the solution is determined by spectrophotometer, the appropriate measuring wavelength should be selected first. The selection is based on the absorption curve of the measured solution. In general, we always choose the maximum absorption wavelength as the measurement wavelength, which can improve the sensitivity. In some cases, the maximum absorption peak is very sharp, the absorption is too large or there is interference nearby, so we can not choose the maximum absorption wavelength, but we must choose other wavelength in the absorption curve to measure with a certain sensitivity. Corresponding wavelength to eliminate interference. Drawing absorption curve is an effective method to select wavelength correctly.