不同傅里叶变换红外光谱法研究土壤光谱特征的比较与应用

为了将傅里叶变换红外光谱技术更好地应用于土壤中官能团的定量分析,通过比较3种不同傅里叶变换技术下土壤特征吸收峰的差异,来选取最佳的光谱技术应用于土壤的相关研究。采用透射(T-FTIR)、衰减全反射(ATR-FTIR)和漫反射(DR-FTIR)3种光谱技术分别对有机物(苯甲酸、硬脂酸)和土壤(辽东栎)进行了分析。并将辽东栎和草地土壤样品按不同比例混合,使用T-FTIR和DR-FTIR对混合土样进行光谱测定,用于定量分析研究。结果表明:(1)有机物样品在3种光谱技术中均出现特征吸收峰,苯甲酸在1 600～1 400 cm^-1出现苯环C=C骨架特征峰,硬脂酸在2 900～2 800 cm^-1显现甲基的特征峰。有机物中羧酸-COOH内羰基-C=O在1 720～1 680 cm^-1出现伸缩振动吸收峰,羟基-OH分别在1 430～1 410 cm^-1,940～930 cm^-1附近出现面内和面外弯曲振动吸收峰。有机物在T-FTIR技术中需要用溴化钾(KBr)对其稀释。(2)辽东栎土壤样品在T-FTIR和DR-FTIR技术测试中发现,其土壤谱图中有较多有效特征吸收峰,土壤样品在T-FTIR技术中也需要用KBr进行稀释并使样品均匀的分布在锭片中; 而ATR-FTIR技术测试中仅出现个别有效特征吸收峰,不利于对土壤谱图鉴别与进一步分析。(3)辽东栎和草地土壤样品按不同比例混合的测试结果表明:T-FTIR和DR-FTIR技术测试中质量分数与峰面积比呈正相关,线性拟合分别为R²=0.70和R²=0.88。土壤在3种不同红外技术中,DR-FTIR光谱具有较好的土壤特征吸收峰,对土壤样品可以不用KBr稀释。测试步骤简单易操作,可用于土壤样品定量分析研究。

Comparison and Application of Different Fourier Transform Infrared Spectroscopy to Soil Spectral Characteristics Analysis

In order to better apply Fourier transform infrared spectroscopy technology to the quantitative analysis of functional groups in soil, three differences of soil characteristic absorption peaks under three Fourier transform technologies were compared to select the optimal spectral technology to be applied to the related research of soil. Transmission(T-FTIR), Attenuated Total Reflectance(ATR-FTIR)and Diffuse Reflectance(DR-FTIR)were used to test and analyze organics(Benzoic Acid and Stearic Acid)and soil samples(Quercus Liaotungensis), and mixed Quercus Liaotungensis and grassland soil samples in different proportions. T-FTIR and DR-FTIR were used to determine the spectrums of mixed soil samples for quantitative analysis. The results show that:(1)characteristic absorption peaks of organics were found in all three spectral techniques. Benzoic acid showed characteristic peak of benzene ring C=C skeleton at 1 600～1 400 cm^-1, searic acid showed characteristic peak of methyl at 2 900～2 800 cm^-1; carbonyl-C=O in carboxylic acid-COOH in organic matter, the stretching vibration absorption peak appeared at 1 720～1 680 cm^-1, hydroxyl -OH had in-plane and out of plane bending vibration absorption peaks near 1 430～1 410 cm^-1 and 940～930 cm^-1, respectively; organics reagents needed to be diluted with potassium bromide(KBr)in the T-FTIR technique;(2)the soil samples of Quercetissima Liaotunica were tested by T-FTIR and DR-FTIR techniques, and there were many effective characteristic absorption peaks in the soil spectrums; the soil samples also needed to be diluted by KBr and distributed evenly in the ingot in T-FTIR technique; however, only a few effective characteristic absorption peaks appeared in ATR-FTIR test, which was not conducive to the identification and further analysis of soil spectrum;(3)the result that soil samples of Quercus Liaotungensis and grassland were mixed in different proportions showed that there was a positive correlation between mass fraction and peak area ratio in T-FTIR and DR-FTIR tests, and the vaulues of R² linear fitting were 0.70 and 0.88, respectively. Among the three different infrared technologies of soil, DR-FTIR spectrum has good characteristic absorption peak spectrum of soil, and soil samples can be diluted without KBr. The testing procedure is simple and easy to operate, which can be applied to quantitative analysis of soil samples.