地氯雷他定(DL)是一种治疗过敏性鼻炎和慢性荨麻疹的经典抗组胺药, 在采用光谱法研究其结构相关的N-H键时, 检测结果会受到不同预处理方式及测试方法的影响。 采用透射模式傅里叶变换红外法(TR-FTIR)对DL进行检测, 常规氯化钾压片法获得的光谱在3 325和3 304 cm^-1处出现2个较弱的峰高约为1:1的N-H伸缩特征吸收峰; 石蜡糊法没有明显信号; 样品先与石蜡混合成糊状再加入氯化钾压片, 则会在3 327和3 304 cm^-1处出现2个峰高约为1:2.3的特征吸收峰; 采用衰减全反射式傅里叶变换红外光谱法(ATR-FTIR)对DL进行检测, 无论是改变ATR晶体类型还是改变仪器的检测器, 此区间几乎检测不出特征峰; 采用漫反射式傅里叶变换红外光谱法(DRS-FTIR), 不需要对样品进行预处理, 能检测出3 327和3 304 cm^-1处2个峰高比约为1:5的特征吸收峰。 采用傅里叶变换拉曼方法(FT-Raman), 无需预处理, 信噪比高, 能检测出3 327和3 304 cm^-1处2个峰高比约为1:6的特征峰; 而分别采用激发波长为532、 633和785 nm的激光拉曼, 荧光信号很强, 1 700 cm^-1以上观察不到任何有用信号。 为了进一步研究预处理过程对DL的影响, 采用差示扫描量热法(DSC)对不同预处理后的样品进行了熔点测试, 结果显示: (1) DL原样熔点为156.4 ℃, DL进行研磨后的样品熔点为156.6 ℃, DL与氯化钾进行物理混合后的样品熔点为156.6 ℃, 说明研磨及物理混合对DL的晶型没有造成破坏; (2) DL与氯化钾一起混合研磨的样品, 熔点为153.0 ℃, 与石蜡混合后熔点为141.5 ℃, 先石蜡制糊再加入氯化钾研磨的试样, 熔点为145.0 ℃, 熔点均比原样明显偏低且熔程变宽, 说明这些预处理可能使原样的结构发生了变化。 为避免预处理过程引入的不确定性, 在对DL进行光谱检测时建议选用DRS-FTIR及FT-Raman方法。

Desloratadine (DL) is a classic antihistamine for treating allergic rhinitis and chronic urticaria. When the structure-related N-H bond is studied using spectroscopy, different pretreatment and testing methods significantly affectthe characteristic absorption peaks with the corresponding height ratio. With Fourier transform infrared transmission method (TR-FTIR), the spectra of DL show obvious differentiation at 3 325 and 3 304 cm^-1 two characteristic absorption peaks with peak height ratio of 1:1, no peak, at 3 327 and 3 304 cm^-1 two peaks with peak height ratio of 1:2.3 respectively corresponding to three different pretreatments of conventional potassium chloride tablet, nujol mull, potassium chloride tablet with nujol mull. Furthermore, the characteristic peaks assigned N-H stretching vibration can hardly be detected using attenuated total reflection FTIR (ATR- FTIR) accessory with neither the crystal type of ATR nor the detector of the instrument changed, indicating the sensitivity of detector also plays an important role. Subsequently, using the diffuse reflection spectrum FTIR method (DRS-FTIR), it is easy to find two characteristic absorption peaks at 3 327 and 3 304 cm^-1 with a peak height ratio of 1:5 without any pretreatment. For the Fourier transform Raman (FT-Raman), two absorption peaks at 3 327 and 3 304 cm^-1with a higher peak height ratio of 1:6 also can be achieved at a high signal-to-noise ratio without pretreatment. For the Laser Raman with the excitation wavelengths of 532, 633 and 785 nm, no useful signal can be observed above 1 700 cm^-1 because of the strong fluorescence. To analyze the effect of pretreatment on the IR N-H band of DL further, differential scanning calorimetry (DSC) is applied to detect the melting point change in the current study. The melting points of 156.4, 156.6 and 156.6 ℃ of the raw DL, the grinding DL and the mixture of DL and KCl indicate that the physical processes of grinding and mixture cannot destroy the crystalline from of DL. The melting points of 153.0, 141.5 and 145.0 ℃ for the ground samples of mixed DL and KCl, mixed with paraffin, and mixed with paraffin and KCl are lower than the raw DL with a broader distance of DSC peaks and indicate the structure change of DL during pretreatment. Therefore, DRS-FTIR and FT-Raman are the suggested methods forspectrum detection to avoid the uncertainty introduced by pretreatment of DL.