Derivatization of Difficult Analytes to Improve GC Elution Behavior

2 Derivatization of Difficult Analytes to Improve GC Elution Behavior 

One way to deal with the recalcitrant compounds described in the preceding paragraph is to modify the troublemaking functional groupfs) to a more tractable form. Their reactivity and polarity are the cause of their bad behavior. We can use this reactivity to add a substituent that converts 

Such agents function less instantaneously than diazomethane. They react faster at quite high temperatures. One way to achieve those has been to mix them with the injection solution. Upon flash vaporization in the hot injection port or the start of the column, the derivatization reaction is nearly instantaneous and complete. This procedure is known as on-column derivatization. Such a mode of introduction of this reagent also achieves the purpose of reacting with and deactivating the free -Si-OH, active site groups in the column, as described at the very end of Section 11.5. This treatment is called silanization. 

The heavy -C4F7 group nevertheless is so much less polar than the -OH it replaced (think Teflon ) that the derivative will elute more easily than the parent compound. An additional advantage is that all those electronegative F atoms yield a derivative with BCD sensitivity, making our analyte 

To summarize, derivatization for GC can confer greater thermal stability to an analyte. It can convert the analyte to a form that is more volatile, less polar, and with less tendency to produce tailing peaks by interaction with column active sites. It can introduce elements into it that make it detectable by more sensitive or selective detectors (remember, in real-world analyses, selectivity often confers more effective sensitivity to an assay). The scope of derivatization for GC is far greater than the several examples listed here. See the bibliography (Grob, Jennings, Scott) or product literature from specialty derivatization agent vendors (Appendix 12.A) for more examples. 

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