应用拉曼和中红外衰减全反射光谱测定溶液和土壤中的硝酸盐

为比较拉曼光谱和红外光谱在溶液和土壤中硝酸盐含量定量分析的适用性,采用两种光谱对溶液和土壤中的NO3–-N含量(0~200 mg/L)进行快速测定。结果表明,溶液中硝酸盐的拉曼特征峰在1 047 cm–1处,该特征峰强度与NO3–-N浓度成正比,对1 035~1 060 cm-1波段拉曼光谱峰面积和NO3–-N含量进行线性回归,决定系数R2为0.995 4;溶液中硝酸盐的中红外衰减全反射光谱特征吸收峰在1 350 cm–1,吸收峰与NO3–-N含量成正比,特征吸收区1 200~1 500 cm–1峰面积与NO3–-N含量的决定系数R2为0.991 1,表明两种光谱都可用于溶液中硝酸盐的测定。对于土壤样品,红外光谱在1 250~1 500 cm–1处有硝酸盐吸收峰,且吸收峰与NO3–-N含量成正比,峰面积与NO3–-N含量之间的决定系数R2为0.968 4;而对于拉曼光谱,硝酸盐的拉曼峰因受较强干扰导致吸收峰不明显,峰面积与NO3–-N含量之间的决定系数R2仅为0.000 9,表明中红外衰减全反射光谱可用于土壤中硝酸盐的测定,而拉曼光谱则很困难。因此,拉曼光谱和中红外衰减全反射光谱都可用于溶液中硝酸盐的测定,且前者灵敏度要高于后者;中红外衰减全反射光谱可用于土壤中硝酸盐的测定,而拉曼光谱难以用于土壤中硝酸盐定量分析,这为硝酸盐的快速测定提供理论依据和技术支持。

Rapid Determination of Nitrate in Solution and Soil Using Raman Spectroscopy and Mid-Infrared Attenuated Total Reflectance Spectroscopy

Raman spectroscopy and mid-infrared attenuated total reflection spectroscopy(ATR) were applied to determine nitrate-N content in solution and in soil. The results showed that the characteristic band of nitrate in solution in Raman spectrum was located 1047 cm_-1, and the intensity of the band increased with the nitrate nitrogen concentration. The linear correlation coefficient (R₂) between band area and nitrate-N content was 0.9954. The characteristic absorption band of nitrate in mid-infrared attenuated total reflection spectrum was in the range of 1200-1500 cm_-1, the absorption band is proportional to nitrate-N content, and the correlation coefficient R₂ between band area and nitrate-N content was 0.9911. For soil samples, the characteristic absorption band of nitrate by ATR was 1250-1500 cm_-1, the absorption band has a significant positive correlation with nitrate, and the correlation coefficient R₂between band area and nitrate-N content was 0.9684. However, the band of nitrate was not obvious by Raman spectroscopy. Therefore, both of two methods could determine nitrate in solution, but the sensitivity of Raman spectroscopy was better than ATR spectroscopy; for soil samples, ATR could be used to predict the nitrate but Raman spectroscopy could not.