Comparative Investigation of the Spectroscopic Behavior Based on High-Concentrated Solution in Nitrogen and Air Atmospheres

In order to accurately obtain photometric information of high concentration SO(4)(2−) and other substances in the process industry, the spectroscopy behavior of SO(4)(2−), S(2−), Ni(2+) and Cu(2+) in air and nitrogen atmosphere was compared based on the UV-visible spectrophotometer with a nitrogen replacing the oxygen. Different from Ni(2+) and Cu(2+), the accuracy of SO(4)(2−) and S(2−) in the ultraviolet region was effectively improved by using a nitrogen atmosphere (P detection results were regressed within the limited standard range, RE < 5%). The nitrogen atmosphere suppressed the additional light attenuation caused by its absorption of ultraviolet rays by isolating oxygen and was also reflected in the decrease in the degree of red shift of the characteristic wavelength for SO(4)(2−) with increasing concentration. Therefore, the detection results of SO(4)(2−) showed an effective improvement in sensitivity. Nevertheless, according to the complementary experimental results and theoretical calculations, in addition to oxygen absorption, the low detection accuracy of SO(4)(2−) high concentration is also attributed to the reduction of the energy required for electronic excitation per unit group caused by the interaction between SO(4)(2−) groups, resulting in a deviation of the C-A curve from linearity at high concentrations. The influence of this intermolecular force on the detection results is far more important than oxygen absorption. The research can provide reliable theoretical guidance and technical support for the pollution-free direct measurement of high-concentration solutions in the process industry and promote the sustainable development of the process industry.