每年各地红外光谱的实验室制备和利用红外光谱仪分析成千上万个样品。 这些样品范围从商业产品像高聚物颗粒和液体表面活性剂，一直到高纯度有机化合物。为了从这些不同的材料中得到高质量的红外谱图，我们必须采用多种多样的制样技术。这篇文章的旨在与您交流红外制样技术。在这篇文章中，将对基于样品的物理特性进行的技术选择作讨论。

液样的制备是将少量样品涂于两片红外透明的窗片（KBr、NaCl等）之间。窗片的互相挤压形成一个样品薄层，样品的成分决定了选择哪种窗片。对于无水的样品，窗片材料是KBr。对于含水样品, KRS-5 较为适合。

固体样品对光谱学家提出挑战。样品的熔点为我们指出首先该考虑哪种技术。

对于熔点低于72^。C的样品，用适当的溶剂将样品溶解，成膜于KBr窗片上是最先考虑的。如果因为基线不好或是溶解性差而不成功，可以考虑在两片KBr窗片内熔化成膜。如果这也不行，样品可进行KBr压片。

对于熔点高于72^。C的样品，首选的技术是KBr压片。对于聚合物样品，成膜法是首选，接着是热熔法和压片法。

对于熔点未知的样品，结晶度的检测将会指明哪种技术将会成功。高结晶度的样品用KBr压片法较好，对于低结晶度的样品，成膜和热熔会得到更好的谱图。

 

分析液体样品的最常用方法就是将一滴液体夹在两片盐片中间，过程如下：将一滴样品滴于合适的盐片上，几秒钟后，将另外一块盐片合上，这样液体被夹在两块盐片之间，变成薄膜状。当然，选用的盐片要与分析的液体样品兼容。不含水的样品可采用KBr（32×5mm）盐片，含水样品则采用KRS-5盐片，这几种晶体材料的选用主要是根据它们在红外段的透光范围（优于4000－450cm-1）和稳定性。每次一个样品做好后，用带合适的溶剂的棉花清洗，然后在倒有甲醇的鹿皮或鸡皮上抛光。

KBr盐片需要经常进行抛光，以维持其表面的光洁。由于KRS-5晶体有毒，所有只有当其表面被划伤或污染时才需要抛光，而且要求专业人员来完成。

水平的单反射ATR主要是由一个ZnSe晶体的凹槽组成，尽管ZnSe晶体的截止频率为650－700CM-1，但它比其它宽频带的材料要更加耐用。

在样品分析好后，要用适当的溶剂将样品冲掉，再用棉花球擦洗干净，这种材料不需要经常抛光。

潜在问题：

但它最大的问题就是样品谱图的非线性，主要指峰位的位置和强度不满足Beer－Lambert法则：

A = abc 这里, A =吸收值

b = 光程

c =浓度

The Beer-Lambert Law is typically discussed in regards to quantitative analysis. Spectral searching is a type of quantitative analysis, since most searching algorithms use band intensity as a factor. Linearity due to sampling typically occurs in transmission analysis and not in ATR, due to the nature of the ATR technique.

Beer-Lambert定理主要是针对定量分析的，谱图检索是定量分析的一种类型，因为谱图检索是以吸收强度为基础的，非线性主要出现在透射中，在ATR中则没有，这主要是由于ATR的技术特点导致的。

The most common cause of non-linearity is inconsistent path length across the sampling area. For our instruments at 2 cm-1 resolution, the sampling area is 6 mm at focus. If there are any air bubbles or unevenness in the sampling area, the path length of the sample will vary across the sample area.

最常见的导致非线性的原因是透过样品的光程的不连续性。分辨率为2时，样品区红外光的聚焦点仅有6MM，如果此时样品区样品厚度薄厚不均或碰巧有气泡或，就会引起此处光程不同。

These variations will cause inaccuracies in the band intensities in the spectrum. In other words, the bands will be weaker or stronger than they should be. This condition will lead to reduced spectral search quality. Figure 1 is a plot of a spectrum of 3,4-dichlorotoluene analyzed as a neat with a consistent path length. The peak intensity of the band at 808 cm-1 is 0.39, while the peak intensity of the adjacent band at 870 cm-1 is 0.24 (A808 cm-1/A870 cm-1 = 1.6).

这些不同将导致谱图在各个波段的吸收强度与实际值产生差异，从而降低谱图检索的质量，图是纯3,4-dichlorotoluene的吸收图，在808 cm-1波段处的吸收度为0.39，邻近870 cm-1处是0.24 (A808 cm-1/A870 cm-1 = 1.6)

Figure 2 is the same sample analyzed with uneven coating of the sample on the crystals. As you can see, the band intensities are different. For this spectrum, the peak intensity of the band at 808 cm-1 is 0.76, while the peak intensity of the adjacent band at 870 cm-1 is 0.62 (A808 cm-1/A870 cm-1 = 1.2). This represents a change of 25% from the previous spectrum. This could lead to a poor spectral search match. We 870 cm-1check for unevenness by analyzing the sample using a 6 mm sampling area, followed by analysis with a 3 mm sampling area. The two spectra are subtracted from each other and the residual spectrum is examined.

图二是同一个样品但是通过在晶体上做成一层薄厚不均的膜而得到的谱图，它的吸收率与上图已经有差别了，808 cm-1处的吸收率是0.76而870 cm-1处却为0.62(A808 cm-1/A870 cm-1 = 1.2)，与图一相比，已有25％的差距，这必然会导致谱图检索结果正确率的下降，将样品聚焦斑为6mm时得到的的图与聚焦斑为3mm时得到的图相减，用差谱的结果来进行分析：

Non-linearities due to unevenness would show up as a large residual. We also minimize unevenness by frequent polishing of the crystals.

由薄厚不均导致的非线性将会使差谱的结果非常明显，我们可以通过定期对晶体进行抛光来降低这种误差。

The second cause of non-linearity in the spectrum of a liquid sample is sample thickness. A large percentage of spectra of liquid samples submitted to us for spectral search analysis have been run too thick. Most FT-IR spectrometers/detectors have a linear response up to approximately 1.2 absorbance units. Any band above 1.2 absorbance units is of questionable linearity. Non-linearitycan sometimes be seen as “choppiness” on the top of the band. We only accept spectra from our lab that have a maximum absorbance value of 1.2 absorbance units. Figure 3 is a plot of the spectrum of the same sample used previously. However, the sample thickness was much larger than the previous spectrum.

经常引起液体样品谱图的非线性的另一个原因是样品的厚度。液样太浓将会导致谱图的吸收太强，而多数红外仪器的检测器的线性响应范围是0到1.2个吸收单元，大于1.2时就会引起线性问题。有时非线性会使谱图中吸收峰的头部成平头状，在我们的实验室中只接受吸收单元1.2的谱图，图三也是上面提到的样品的谱图，但样品的厚度却远远大于前者。

The strongest band in the spectrum is over 30 absorbance units. For this spectrum, the peak intensity of the band at 808 cm-1 is 1.66, while the peak intensity of the adjacent band at 870 cm-1 is 0.94 (A808 cm-1/A870 cm-1 = 1.76).

This represents a change in relative intensity of 10%, compared to the normal spectrum in Figure 1. This change in relative band intensities will have a negative effect on search accuracy.

谱图中最强的吸收单元已经超过了30个吸收单元，808 cm-1处的吸收度为1.66，870 cm-1处为0.94(A808 cm-1/A870 cm-1 = 1.76)，相比而言，产生了10％的误差，这种不同波段的吸收值的相对性的差异将会给谱图检索带来负面影响

 

 

 

在 Sadtler的实验室，涂膜技术是用在熔点低于72^。C的样品和低结晶度的样品，比如象高聚物，涂膜法也可在其他方法失败后试用。

先将样品溶于适当的溶剂中。然后将数滴溶液滴于惰性的基质上，溶液挥发后在基质上留下一层薄膜。如果惰性基质是红外透明的，可直接检测或将薄膜剥下检测。

选择溶液最主要的标准是容易去除（除了最明显的一点，可溶解样品）。这意味着必须要有低的沸点。蒸发溶剂所需的热量越少，样品所受的影响就越小。另外，溶剂越容易去除，越少的溶剂将会留下。在我们的实验室，以下列出的溶剂将首先考虑：氯仿(BP. 61.2° C)，丙酮(BP. 56.2° C)，三氯乙醇(BP. 151° C)，邻二氯苯(BP. 180.5° C)和水(BP. 100° C)。在选择成膜技术时这五种溶剂适用于85％的样品。

纯溶液的光谱也应准备着作为参照。将溶剂的谱图与成膜样品的谱图作比较是判断是否有溶剂残留的一个好方法。每取用一次溶剂便将其参比谱图更新一下也是一个好习惯

在 Sadtler的实验室，没有试图将薄膜从基质上取下，基质和薄膜是一起放入光谱仪的。所以需要对红外透明的基质。除了溶剂是水采用KRS-5晶体外，一般最常用的基质是KBr晶体。如果决定将薄膜取下，玻璃将是不错的选择。

经验告诉我们最好使用少量的稀溶液（3－5滴），在基质上形成几层薄膜，这将比用浓溶液形成的厚膜和大量的溶液一次成膜要好的多.这将使薄膜中的溶剂残留最少。有时，当你成膜的是晶体样品，谱图上会显示非常严重的散射和基线倾斜。这在单层成膜时经常发生，在多层成膜时也会出现。我们认为这是因为最先沉淀的晶体成为了形成大晶体的晶核，正是这些大晶体造成光的散射，使基线倾斜。在我们实验室为了防止这种问题的发生，我们经常在晶体的两面都涂上一层薄膜，有时在两块晶体的两面都涂上一层薄膜，一共形成四层膜。这个能解决绝大部分的散射问题。

在蒸发溶剂时，使晶体上的溶液保持流动。这将帮助您得到厚度均匀的膜。我们经常将晶体放在一小片可反复使用的纸卡上（大约2”×3”），后不停的敲击纸卡的背面，使溶液保持流动，或者用移液管末端不停的搅拌搅拌如果去除溶剂需要加热，而晶体又是水溶性物质，比如KBr，那你应该先加热卡片，去除其中含有的水汽。如果你不这样作，晶体的底部会吸水雾化，这将使你的谱图的基线倾斜。在我们的实验室，我们使用加热灯来慢慢清除水汽，如果是在一个较为的环境中，因该一直用灯加热以去除环境中水汽的影响。注意任何必须预防的情况，尤其是在使用易燃溶剂时。

在成膜技术中最严重的两个问题是薄膜厚度不均匀和溶剂残留。薄膜的厚度不均将导致谱图的非线性。而在薄膜技术中应该时刻注意溶剂残留的问题。总是将结果谱图与溶剂谱图的主峰作比较。如果结果显示有溶剂残留，有时可通过继续加热来去除溶剂。

如果你不能确定某个特征峰是溶剂还是样品产生，那样品必须用另一种方法检测或使用另一种不会产生该特征峰的溶剂。

另一个可能产生的问题是，某些样品在加热和有氧气的情况下易发生氧化。这将导致在1740 cm-1上有一个C=O 的小峰。

有几种方法可以防止或最小化这种氧化。在惰性气氛中蒸发溶剂，比如在氮气中，这样可以减少氧气的存在。或是减少加热量来化小这个问题。可能的话，你可以使用更低沸点的溶剂，或用真空泵来抽取溶剂。

In Sadtler's laboratories, the film technique is used for samples with melting points below 72°C and for samples with low crystallinity, such as polymers. The film technique is also attempted when other methods fail to produce a good spectrum.

在萨特勒实验室，制膜技术主要应用于熔点小于72°C而且是低结晶率的样品，例如聚合物，有时当一个样品用其它方法都作不出好图时，也会采用制膜法。

The sample is first dissolved in a suitable solvent. Several drops of the solution are then placed on an inert substrate and the solvent is evaporated off leaving behind a thin film of the sample on the substrate. The film is then either peeled off and placed in the spectrometer; or, if the substrate is transparent in the infrared, the substrate with the sample can be placed into the spectrometer.

首先将样品溶到溶剂中 ，滴几滴溶液放到惰性基底上，将溶剂蒸发，然后在基底上留下一层薄膜，再将薄膜揭下来放到仪器中作图。如果惰性基底能透红外光，可将它们一块放到仪器中测量。

The main criterion for a solvent (besides the obvious one, dissolving the sample) is that it should be easy to remove. This implies a low boiling solvent. The less heat applied to evaporate the solvent, the less the sample will be affected. In addition, the easier it is to remove the solvent, the less solvent will be left behind.

对溶液而言，最关键的是要便于分离，即溶的沸点低，稍微加热即可将溶剂挥发而溶质几乎不受影响，而且溶液越容易分离，溶剂挥发的就越干净。

In our laboratories, the following list of solvents are attempted first: chloroform (BP. 61.2° C), acetone (BP. 56.2° C), trichloroethanol (BP. 151° C), o-dichlorobenzene (BP. 180.5° C), and water (BP. 100° C). These five solvents are suitable for about 85% of the samples for which the film technique is attempted. The spectra of the pure solvents should also be kept on hand as a reference.

在我们实验室，常用下列溶剂：chloroform (BP. 61.2° C), acetone (BP. 56.2° C), trichloroethanol (BP. 151° C), o-dichlorobenzene (BP. 180.5° C), 和 water (BP. 100° C). 对准备采用制膜测量的样品，85％的样品可运用上述的五种溶剂，纯溶剂还可用来测参考谱图。

Comparison of the solvent’s spectrum to the cast film is considered mandatory to determine if any solvent was left behind. It is also a good practice to generate a new reference spectrum each time a solvent is reordered.

对照纯溶剂的谱图，可检验是否有溶剂遗留在样品中，同时样品的谱图又可作为经过重新处理的样品的谱图的参照图。

In Sadtler's laboratories, no attempt is made to peel the film off the substrate. The substrate is placed with the film into the spectrometer. Therefore a sub-strate which is transparent in the infrared is needed. The most common choice is a KBr crystal unless the solvent is water, in which case a KRS-5 crystal is used. If the decision is made to peel off the film, then glass is generally a good choice.

在萨特勒实验室，从不直接从基底上撕膜，而是直接将基底带膜一块放到仪器中，这就需要一个对红外 光完全不吸收的基底，只有溶剂不是水，大多数我们都采用KBr晶体，如果是水则用KRS-5，如要揭膜下来，完全可以采用玻璃作基底。

It is our experience that it is best to use a small amount of a dilute solution (3-5 drops) and cast several thin films on top of each other, rather than to produce one thick film from a concentrated solution or from using a large amount of the solution. This minimizes the possibility of trapping any solvent within the film.

我们在实验中，经常只采用3－5滴经过稀释的溶液，重复的浇多次薄膜，而不是用浓溶液作一张厚膜或是用大量的溶液，这都是为了尽可能减少遗留在薄膜中的溶剂。

Sometimes, when casting films of crystalline materials, a spectrum may show a significant amount of scattering and give a poor sloping baseline. This problem is more common when trying to cast a single thick film, but also occurs when casting several thin films on top of each other. It is our belief that this is a result of the first crystals precipitating out and acting as ”seed” crystals to produce larger crystals. It is these large crystals which cause the light to be scattered, hence a poor baseline. To avoid this problem in our laboratories, we will often cast a thin film on both surfaces of the crystal, and occasionally on both surfaces of two crystals, resulting in a total of four thin films. This technique corrects most scattering problems.

有时，当我们铸成膜后，在谱图中会由于散射而导致基线倾斜，多数情况是出现在一次性浇铸成的厚膜上，有时经多次浇铸的薄膜也会出现这种情况。首先我们要相信这是晶体沉淀的结果，即就象晶体‘种子“逐渐生成大晶体一样。大晶体容易引起散射从而出现基线倾斜，为了避免这种情况，我们实验室经常在晶体的两面同时铸膜，偶尔也会在两块晶体的两面进行，总共生成四层膜，以解决散射问题。

When evaporating off the solvent, keep the solution moving over the crystal. This will help you get a film of even thickness. We usually place the crystal on a small disposable cardboard card (about 2” x 3”) and either rock the card back and forth to keep the solution moving, or use the end of the pipet to smear the solution over the crystal. If heat is required to remove the solvent and the crystal is a hydroscopic material such as KBr, then you should first heat the card to drive off any residual moisture in the card. If you do not do this, the bottom surface of the crystal will absorb this moisture and cause it to become cloudy, which can cause a sloping baseline in your spectrum.

在溶剂蒸发过程中，尽量使溶液在基底上不停流动，这将有助于得到一张薄厚均匀的膜。具体方法是将浇有溶液的晶体放在一块小板子（2” x 3”）上，然后前后晃动板子，使溶液不停运动，或者可以用吸耳秋不停的对着溶液吹，如果需要加热，而基底又类似KBr之类，那您需要先对基底加热出湿，如果不这样，基底将会吸湿潮解，从而引起谱图的基线不准。

In our laboratories, we use a heat lamp to gently evaporate off the solvent. This should always be done in a fume hood to remove the vapors from the lab environment. Observe all necessary precautions, especially when working with flammable solvents.

在我们实验室中，常常使用红外照灯，除去环境中的湿汽，切记不可用于可燃性溶液。

The two most serious problems that can occur with the film technique are an uneven film or residual solvent in the spectrum. The problem with an uneven film is spectral non-linearity. The problem of a residual solvent must be vigilantly searched for whenever the film technique is used. Always check the resulting spectrum for the major bands of the solvent. If it appears that some solvent remains in the spectrum, it is sometimes possible to drive off the last of the solvent by applying more heat.

制膜过程中，薄厚不均和溶剂分离不干净是常出现的问题，前者容易引起谱图非线性，而后者则会影响谱图检索，当应用制膜技术时，要注意观察溶质谱图的特征峰，以判断是否有溶剂遗留，如果有继续加热。

If you are still unsure whether the sample or the solvent caused a particular band, then the sample must be re-run using a different technique or a different solvent which does not contain that band.

如果你不能确定样品或溶质谱图的特征峰，则需要再采用其它技术或者用不同的溶剂，多的几张图。在加以比较。

Another possible problem is that some samples may oxidize easily in the presence of heat and oxygen. This often results in a small band in the C=O region around 1740 cm-1.

其它可能的出现的问题是在加热过程中，容易使样品氧化，主要会在1740 cm-1处产生变化。

There are several ways to prevent or minimize this oxidation. Evaporating off the solvent in an inert atmosphere such as nitrogen, reduces the availability of oxygen. Applying less heat will also minimize the problem. You can use less heat by changing to a lower boiling solvent if possible, or by removing the solvent in a vacuum oven.

避免或降低氧化的措施就是将溶剂蒸发过程放惰性气体氛围中进行，如氮气，尽可能减少氧的含量，或者少加些热，尤其在溶剂的沸点很低时。要么将分离过程放真空中进行。