Ultraviolet-visible spectrophotometer is a optical spectrum instrument widely used in laboratories. According to the optical structure, the UV-Vis spectrophotometer can be divided into two types: single beam and double beam. In comparison, the double beam UV-Vis spectrophotometer can eliminate the error between the reference and the sample cuvette and remove the influence of factors such as the unstable light source and the sensitivity change of the receiver, which is especially suitable for sample structure analysis.
When choosing a UV-Vis spectrophotometer, it is mainly considered from six aspects: photometric accuracy, stray light, spectral bandwidth, stability, noise, wavelength accuracy and repeatability.
I. Photometric accuracy
Photometric accuracy refers to the difference between the actual measured photometric reading value and the true value. It can directly reflect the accuracy of the test data of the instrument, and is the direct requirement of the user on the instrument.
II. Stray light
Stray light refers to incident light of other wavelengths far away from the absorbed light. In other words, there should be light where there should not be light. It determines the concentration range of the sample analyzed by the instrument, especially the upper limit of the concentration. When the stray light of an ultraviolet-visible spectrophotometer is constant, the greater the concentration of the sample being analyzed, the greater the analysis error. It can bend the established standard curve and is the main source of error in the spectrum measurement. Of course, the smaller the value, the better.
III. Spectral bandwidth
Spectral bandwidth refers to the band width at 1/2 height of the intensity profile of the monochromatic spectral line emitted from the monochromator. According to Beer's law, the spectral bandwidth should be as small as possible. However, if the light source energy of the instrument is weak and the sensitivity of the optical sensor is low, the spectral bandwidth is small, then ideal measurement results cannot be obtained. Therefore, please pay attention to this when choosing and using the instrument.
Stability is one of the most important indicators for users. The purpose of the instrument is to be stable and reliable, if it is unstable, let alone reliable.
Noise is also one of the important indicators of the instrument. It mainly affects or limits the lower limit of the concentration of the tested samples.
VI. Wavelength accuracy and repeatability
Each value of the instrument is measured at a certain wavelength. If the indicated wavelength sharply deviates from the actual wavelength, then the agreement between the measured value and the true value will not be guaranteed. This shows the importance of this indicator.