The Applications Of Infrared Hybrid Spectrometry In Inorganic Salt Solution Systems

Infrared spectroscopy?IR?is one of the most important methods for qualitative,quantitative,and structural analysis.IR technology has the characteristics of simple operations,fast detections and small sample amount needed.The IR spectra of almost all types of samples such as gas,liquid,and solid samples can be obtained.What's more,the price of IR spectrometer is relatively low and its penetration rate is high.All of these advantages make IR widely used in chemical industry,environment,medicine,biology,agriculture,food,environmental monitoring and other fields.Water is one of the most common solvents,so aqueous solutions appear frequently in the infrared spectra detection.In this paper,the attenuation total reflection?ATR?technology is used to study the infrared spectra of aqueous solutions.Different inorganic salt aqueous solutions have been studied by IR spectra.With the change of the concentration of solution,the infrared spectrum of water changes greatly.The absorption peaks intensity change and their position also shift.So these systems don't meet the Lambert-Beer law.If the spectral subtraction technique is used to eliminate water absorption peaks,the result will inevitably be unsatisfactory.In order to solve this problem,we introduced the hybrid absorbance spectrum and simulated the real spectrum by bilateral clipping principle.Assuming that the IR spectra of inorganic salt aqueous solutions with concentrations c1 and c2 are A_c1 and A_c2,the hybrid absorbance spectrum is defined as:A_hc=aAca+bA_c2.A_hc contains both A_c1 and A_c2 component,so it is called the hybrid spectrum.To ensure that A_hc is highly similar to the real spectrum Ac,c must be between c1 and c2.This paper uses binary linear regression analysis with A_c1 and A_c2 as independent variables to obtain the hybrid spectrum A_hc by selecting the appropriate regression coefficients,which can replace the real spectrum Ac.The concentration c?c1c<c2?is linearly related to the regression coefficients.As long as the concentration c is selected,the regression coefficients a and b can be obtained.Then the hybrid spectrum A_hc=dA_c1+bA_c2 is obtained.Because A_hc is highly similar to Ac,the substitute of real spectrum can be obtained without preparing the sample.We used the pause function of the spectrometer and the double background samples method.Background 1 is the sample with c1 concentration,which is scanned N₁ times.Background 2 is the sample with c2 concentration that is scanned N₂ times.The desired hybrid background single beam spectrum can be obtained through adjusting the ratio of N₁ to N₂.Then the high-quality IR spectrum is obtained.The hybrid spectrum and the bilateral clipping principle have been successfully applied in systems deviating from the Lambert-Beer law.Hybrid spectrum technology is simple and efficient,and provides a new method for the IR study of multi-component systems,especially for the system that doesn't meet the Lambert-Beer law.