不同分辨率下气体样品傅里叶变换红外光谱的定量分析误差

通过分析牧场附近测量的大气FTIR光谱中NH3在4种分辨率(分别为1、2、4cm-1和8cm-1)下的浓度,系统研究了不同分辨率下气体样品FTIR光谱定量分析的误差。选择72个实测光谱作为研究对象,其中NH3的光程积分浓度(Path-integrated concentration,PIC)分布在40—1300(μmol/mol).m。分析了NH3的最大吸收峰和次大吸收峰的选取对定量的影响。结果表明:选用NH3的次大吸收峰的定量误差更小;在允许的误差范围内(本研究中设为5%),不需要制作校准曲线,通过选用多个浓度适当的参考光谱,直接应用Beer定律仍能实现气体样品的定量分析;并且分辨率越低,定量分析所需的参考光谱数目越多。本研究通过合理选用多个参考光谱,实现了不同分辨率下FTIR光谱的定量分析;既充分利用了Beer定律,又克服了吸光度-浓度在低分辨率下的非线性问题;为不同分辨率下气体样品FTIR光谱的定量分析提供了参考。

Errors in Quantitative Analysis for Fourier Transform Infrared Spectra of Gas Samples at Different Resolutions

Fourier transform infrared spectra of air around animal farms were measured.By analyzing the concentrations of NH3 at four resolutions,1,2,4cm-1 and 8cm-1,errors of quantitative analysis for FTIR spectra of gas samples at different resolutions were systematically investigated.The path-integrated concentration of NH3 was distributed in the range of 40—1300(μmol/mol)·m by selecting 72 actual measurement spectra as object of study.The effect of selecting maximum and second largest absorbance peak of NH3 on quantification was studied.The results showed that the quantitative error calculated with the second largest peak absorbance was smaller than that calculated with the largest peak absorbance.Choosing reference spectra of multiple concentrations,the quantitative analysis of gas samples can be achieved by directly applying Beer’s law without drawing calibration curve in the allowable error range(5%,in this paper),and the lower the resolution was,the more number of reference spectra needed by quantitative analysis were.The quantitative analysis of FTIR spetra in different resolution was realized by choosing multiple reference spectra,which adequately utilized Beer’s law and overcame the nolinear question of absorbance-concentration in low resolution.It offers the reference for quantitative analysis of FTIR spetra of gas samples in different resolution.