If the sample you test contains different types of substances, its maximum ultraviolet absorption wavelength must be different. The significance of setting dual wavelengths is to ensure that both substances you need to detect and observe can be detected at their maximum absorption wavelength, so that the detection sensitivity will be the highest and the results will be more reliable.

Let me give you an example. For example, the signal-to-noise ratio (S/N) of a certain concentration of substance A at the wavelength of 220nm just meets the quantitative limit. If it is detected at its non-maximum absorption wavelength, its signal-to-noise ratio (S/N) will be less than 10, which will not meet the quantitative requirements, so it will cause quantitative difficulties for the detection of some trace substances and increase various costs brought by pretreatment.

Therefore, the significance of dual-wavelength setting is to ensure that every substance can be detected at its maximum absorption wavelength and every substance can be detected under its most sensitive detection conditions.

My knowledge is limited and I can only answer so much. I hope to answer my doubts and look forward to the expert's answer. Let's discuss it together!