红外(IR)光谱是进行物质结构分析常用的工具, 广泛应用于各种固态、 液态、 气态材料的分析检测。 由于测试方法和制样过程直接影响IR测试结果的准确性, 研究了比较常用的衰减全反射(ATR)法与透射(TR)法在固体物质的IR光谱测试中的优劣。 选取3种常见高分子、 3种无机物以及3种有机小分子化合物作为研究对象, 分别用ATR法和TR法测试其IR光谱。 结合制样过程及谱图解析, 对谱图中异常现象进行了深入剖析。 TR法制样复杂、 干扰因素多: 样品与KBr混合研磨过程易吸收空气中水分, 对含N—H和O—H基团的样品分析会造成干扰; 样品太浓或太厚谱图会出现平头峰, 导致谱图无法解析; 样品颜色太深重时, 样片透光性差, 吸收峰强度整体减弱。 与TR法相比, ATR法无需制样, 省时省力且减少了吸水的可能性。 ATR法吸收峰的整体强度小于TR法, 因方法原理不同造成的。 尽管ATR法吸收峰的波数小于TR法几到几十cm-1, 但出峰位置在合理范围内, 定性分析不受影响。 由于ATR法测试时光进入样品的深度很浅(仅2~15 μm), 故谱图不会出现平头峰。 由于短波长的光不能穿透样品那么深, 故ATR法谱图中吸收峰的强度随波长的减小而减弱, 导致官能团区峰强度显著减小、 指纹区峰强度大大增强, 此问题可通过测试软件的“ATR校正”功能修正, 也可在定量分析中加以利用: 以测试的原始谱图对指纹区吸收峰定量, 以校正后谱图对官能团区吸收峰定量。 相比之下, ATR法不受样品颜色、 形状、 厚度限制, 测试简便、 快速、 准确、 无损、 样品可回收, 在高分子、 颜色深重以及易吸湿物质的IR测试上有明显优势。 故推荐广泛使用ATR法进行固体IR光谱检测。

Infrared (IR) spectroscopy is a common tool for material structure analysis, which is widely used in the detection of various solid, liquid and gaseous materials. Since the testing methods and sample preparation process directly affect the accuracy of IR spectra, the comparative study on the attenuated total reflection (ATR) and transmission (TR) methods used in measuring the IR spectroscopy of solid substances was carried out in this paper. Three kinds of common polymers, 3 kinds of inorganic substances, and 3 kinds of organic small-molecule compounds were selected as the research objects, and their IR spectra were measured by both ATR and TR methods, respectively. Various abnormal phenomena in the IR spectra were deeply analyzed combining sample preparation process and spectrum analysis. The TR method is complicated in the sample preparation process and has many interfering factors: the sample is easy to absorb moisture from the air during mixing and grinding process with KBr, which will disturb the analysis of samples having N—H and O—H groups; the spectrum will appear flat-headed peaks and can’t be analyzed as the sample is too thick, and the absorption intensity of the whole spectrum will decrease as the sample is dark colored. Compared with the TR method, the ATR method requires no sample preparation, which saves both time and labor and reduces the possibility of water absorption. Because the method principle is different, the overall absorption intensity of the ATR method is less than that of the TR method. Although the peak wavenumber of the ATR method is generally smaller than that of the TR method among several to dozens of cm-1, the peak position is in a reasonable range, and the qualitative analysis is unaffected. Because the depth of light enters the sample is limited in the ATR method, only 2~15 μm, no flat-headed peaks appear in the ATR-IR spectrum. Due to the short wavelength light cannot penetrate the sample too deep, thus, the absorption intensity in ATR-IR spectrum will weaken along with the decrease of wavelength, which leads to the peak intensity in functional group region decrease and in fingerprint region greatly increases, while this problem can be revised by the “ATR correction” function of software, and also can be used in the quantitative analysis: the original spectra for analyzing the peaks in the fingerprint region, and the revised spectra for analyzing the peaks in functional group region. In comparison, the ATR method is not limited by the color, shape and thickness of the sample, i.e., the measurement is easier, fast, accurate, non-destructive, and recyclable. It has obvious advantages in the IR spectra detection of polymer, dark colored and hygroscopic substances. Thus, it is recommended to widely use the ATR method for detecting IR spectra of solid substances.