衰减的总反射率（ATR） - 一种多功能的FT-IR抽样工具

FT-IR Spectroscopy is an acknowledged tool for identification and characterization of materials on the basis of presence of functional groups present. The technique has been abundantly used for analysis of solids, liquids and gaseous samples. However, in most cases some sample treatment becomes necessary to get meaningful results.

传统上，已经使用传输分析模式分析了液体和固体。可以将液体直接倒入具有可调节垫片的细胞中，并用碱卤化物（kbr粉）均质固体均匀地均匀地反射。总反射率提供了更方便的直接检查此类样品的方法。

什么是ATR？

减弱的总反射率是基于通过晶体样品界面的多种内部反射来测量内部反射的IR光束。光束被引向与样品（液体或固体粉末）紧密接触的晶体的基础板。在每次反射上，光束进入样品的几微米厚度（0.5-5.0μ），并从每个反射中的evaneascent波回到入射光束中。梁在样品吸收IR能量的波长处减弱或减小。当样品与晶体接触时，光谱的质量将是好的，并且晶体材料的折射率显着高于样品的折射率。

ATR技术提供的好处

Before going into the benefits of ATR it is necessary to go into the problems encountered in analysis of liquids and solids by conventional methods.

液体

液体are sampled in specially designed cells that provide a thin film for transmission studies or after preparing a mull with a mineral oil (nujol).

显然，这似乎很简单，但是通常会遇到一些实际问题。

• 密封的细胞具有固定的液膜厚度。在可降低的细胞中，膜厚度不可调节。
• 密封的电池不容易清洁，很难将粘在内壁上的任何气泡移开。
• The film thickness is adjustable in demountable cells but requires insertion of fixed width inert Teflon spacers.

Solids

可以在薄膜支架上支撑薄膜，以安装在样品舱内进行传输研究。然而，优质粉末与kbr粉密切地磨碎，并使用液压压力机进行传输模式的研究制成透明的颗粒。

• KBR本质上是吸湿性的，因此需要仔细的储存和安装在颗粒架内。
• Making the KBr pellet is a skilled operation. The sample and KBr powder should be mixed in correct proportions. Proper grinding is followed by making use of the hydraulic press to transform the mixture to a transparent pellet.
• KBr pellets require careful handling as they are fragile and absorb moisture which can result in cloudiness even before scanning.
• 橡胶，弹性体，纤维等样品不适合用KBR研磨，需要替代样品处理程序。
• 样品与Kbr粉化学反应的可能性。

The problems encountered can be easily overcome by making use of different ATR accessories depending on the nature of sample to be analyzed. The common configurations are HATR or Horizontal ATR which is useful for analysis of common liquids, oils and greases, slurries, pastes, fine powders, thin films and rubber sheets. Diamond tipped accessories are useful for ATR studies on small size or thin samples such as fibers, polymers, biological specimens, etc.

因此，ATR无需样品准备就可以直接分析。另一个关键好处是

• Saving of time due to no need for sample preparation
• Range of crystal materials available with different refractive indices and hardness properties provide suitable options for analysis of different categories of samples.
• 水在MID-IR区域中吸收强烈，因此在水溶液上不可能进行传播研究，但是随着IR吸收样品的吸收在ATR中最小化，它提供了一种可行的方法来分析此类样品。

ATR技术的主要缺点是需要车eful handling of delicate accessories and thorough cleaning before next use so that remnants of samples of earlier analysis do not result in generation of unreliable results.