Spray Reagents
Spray Reagents
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喷雾试剂
DOI：
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发表时间：
2003
期刊：
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通讯作者：
P. Wall
中科院分区：
文献类型：
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作者：
P. Wall
显色薄层板上色谱区的检测通常依赖于可见光或紫外光范围内电磁辐射的吸收或发射。有些化合物是可见的颜色，其他吸收紫外线或显示荧光时，由紫外线或可见光激发，但大多数需要可视化使用适当的喷雾或浸渍试剂。由于薄层色谱（TLC）层中常用的吸附剂的惰性性质，化学反应可以原位进行，而不会破坏吸附剂或粘合剂的特性。存在许多用于TLC的这样的检测试剂，并且在许多出版物中已经整理了制剂列表。与TLC程序的许多其他功能一样，这突出了薄层色谱与其他色谱技术相比的多功能性和独特性。通常，可以使用相当强的试剂如盐酸或硫酸来原位检测分离的分析物。这些试剂与碘蒸气或硝酸蒸气一起沿着作为通用试剂被包括，其可用于使各种不同类型的化合物可视化。其中一些可以称为破坏性试剂，特别是那些涉及炭化。有些试剂对醇类、醛类、酮类、酯类或酸类化合物具有更高的特异性。这些被称为基团特异性试剂。关于特异性，这是可能的极限，因为不存在真正的物质特异性试剂。当在色谱层上没有不可逆的化学反应用于检测时，可视化的形式被称为非破坏性的。非破坏性技术包括可见光和紫外光，有时使用碘或氨蒸气。包括后两种试剂，因为在许多情况下，“反应”是可逆的。通常，分离的化合物可以通过上述技术的组合来检测和可视化。可以首先使用非破坏性技术，然后使用通用试剂，然后使用基团特异性试剂以提高选择性和灵敏度。通常，对于特定的分析物，可能有几种可视化试剂可用，但它们之间的检测灵敏度通常存在明显差异。稳定性也可以在选择合适的检测试剂中起重要作用。有些试剂在数周内具有良好的稳定性，然而，有些试剂必须新鲜配制并几乎立即使用。可视化的色谱区的稳定性也可能不同。一些可能很快褪色，而另一些虽然保持稳定，但随着背景变暗或以其他方式受到试剂的影响而变得更加难以可视化。幸运的是，大多数试剂确实给出了可接受的稳定结果。有时，将色谱层暴露于酸性或碱性蒸汽中，可以使深色或彩色背景变亮。然而，所有这些影响都需要考虑在内，以便使用最有效的可视化程序。在可视化之后，除了除去一些或全部分离的色谱区用于通过红外（IR）、拉曼、核磁共振（NMR）、质谱（MS）或放射照相术的进一步分析之外，还可以通过在吸光度、荧光猝灭或荧光模式下的原位光谱密度扫描进行进一步分析。使用这些联用技术，可以获得更有用的分析数据。事实上，薄层的稳定性和检测到的发色团通常允许收集有用的数据，即使TLC板在几天或几周前已经显影。
The detection of chromatographic zones on a developed thin-layer plate usually relies on the absorption or emission of electromagnetic radiation in the visible or ultraviolet range. Some compounds are visibly coloured, others absorb UV light or exhibit Suorescence when excited by UV or visible light, but most require visualization using an appropriate spraying or dipping reagent. Due to the inert nature of the adsorbents commonly used in thin-layer chromatography (TLC) layers, chemical reactions can be carried out in situ without destroying the adsorbent or binder characteristics. Many such detection reagents exist for TLC, and lists of formulations have been collated in a number of publications. Like a number of other features of the TLC procedure, this highlights the versatility and uniqueness of thin-layer chromatography compared with other chromatographic techniques. Often, quite aggressive reagents such as hydrochloric acid or sulfuric acid can be used to detect separated analytes in situ. Such reagents are included along with iodine vapour or nitric acid vapour as universal reagents that can be used to visualize a wide range of compounds of different types. Some of these can be termed destructive reagents, particularly those involving charring. Some reagents are much more speciRc for groups of compounds such as alcohols, aldehydes, ketones, esters or acids. These are termed group-speciRc reagents. With regard to speciRcity, this is about the limit of what is possible as no genuine substance-speciRc reagents exist. When no irreversible chemical reaction is used for detection on the chromatographic layer, the form of visualization is termed non-destructive. Included in non-destructive techniques are visible and UV light, and sometimes the use of iodine or ammonia vapour. The latter two reagents are included as in many cases the ‘reaction’ is reversible. Often, separated compounds can be detected and visualized by a combination of the above techniques. A non-destructive technique may be used initially, followed by a universal reagent, and then Rnally a group-speciRc reagent to enhance selectivity and sensitivity. Often, for a particular analyte there may be several visualization reagents available, but usually there is a noticeable difference in sensitivity of detection between them. Also stability may play an important part in the selection of a suitable detection reagent. Some reagents have good stability over a number of weeks, however, there are those that must be made up fresh and used almost immediately. The visualized chromatographic zones may also differ in stability. Some may fade quite quickly, whilst others, although remaining stable, become more difRcult to visualize as the background darkens or is affected in some other way by the reagent. Fortunately, the majority of reagents do give acceptably stable results. Sometimes dark or coloured backgrounds can be lightened by exposure of the chromatographic layer to acidic or alkaline vapours. However, all these effects will need to be taken into consideration so that the most effective visualization procedure is used. After visualization, further analysis can be performed by in situ spectrodensitometric scanning in the absorbance, Suorescence quenching, or Suorescence modes, in addition to removing some or all of the separated chromatographic zone for further analysis by infrared (IR), Raman, nuclear magnetic resonance (NMR), mass spectrometry (MS) or radiography. Using these hyphenated techniques, more useful analytical data can be obtained. In fact, the stability of the layers and the detected chromophores often allow useful data to be collected even if the TLC plate had been developed some days or weeks previously.