Matousek P, Parker A W
Central Laser Facility, CCLRC Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX, UK.
Appl Spectrosc. 2006 Dec;60(12):1353-7. doi: 10.1366/000370206779321463.
We compare and contrast two Raman collection geometries, backscattering and transmission, to identify their potential for monitoring the bulk chemical composition of turbid media. The experiments performed on pharmaceutical tablets confirm the expected strong bias of the backscattering Raman collection towards surface layers of the probed sample. However, this bias is largely absent with the transmission geometry, exhibiting gross insensitivity to the depth of impurities within the sample. The results are supported by Monte-Carlo simulations. The applicability of transmission geometry to tablets without any thinning is possible because of long migration times of Raman photons in non-absorbing powder media. The absolute measured intensity of the Raman signal was only 12 times lower in transmission geometry compared with backscattering geometry for a standard paracetamol tablet with a thickness of 3.9 mm. This makes detection relatively straightforward, and detectable Raman signals were observed even after propagation through three paracetamol tablets. Given its properties and instrumental simplicity, the transmission method is particularly well suited to the on-line analysis of bulk content of tablets in pharmaceutical applications.
我们比较并对比了两种拉曼采集几何结构，即背散射和透射，以确定它们在监测混浊介质整体化学成分方面的潜力。在药片片剂上进行的实验证实了背散射拉曼采集对被探测样品表层存在预期的强烈偏差。然而，透射几何结构在很大程度上不存在这种偏差，对样品中杂质的深度表现出总体不敏感性。结果得到了蒙特卡罗模拟的支持。由于拉曼光子在非吸收性粉末介质中的迁移时间较长，透射几何结构适用于无需任何减薄处理的片剂。对于厚度为3.9毫米的标准扑热息痛片剂，透射几何结构中拉曼信号的绝对测量强度仅比背散射几何结构低12倍。这使得检测相对简单，即使在通过三片扑热息痛片剂传播后仍能观察到可检测的拉曼信号。鉴于其特性和仪器的简易性，透射方法特别适合于制药应用中片剂整体含量的在线分析。
