.derivatization procedure for GC-MS (Part I)

Since the introduction of gas chromatographic methods in the earliest sixties allowed a qualitative advance in the potentiality for detection of many organic compounds. Volatility and Stabilization are two things that must be required by organic compounds to have a qualified result of GC and GC-MS analysis.

Figure 1. Example of GC-MS Analysis, Methyl Oleate

Based on those aims, Derivatization is mandatory for polar, thermolabile, or high-mass-compounds to make them amenable to chromatographic analysis.

The preparation of a derivative may also be performed when the mass spectrum of underivatized molecule shows poor diagnostic ions. The chemical structure of the substance is changed after derivatization and, in consequence, the fragmentation pattern can be radically altered. Mass spectra with ions of higher m/z ratios and higher abundance can be obtained. For this identification purposes, the monitoring of at least three ions and their abundance ratios is usually required.

In GC-MS, derivatization can also be used to enhance the detectability of a compound by introducing groups with high electron affinity, such as halogen atoms, that can produce an increase in the ionization efficiency under Negative Chemical Ionization (NCI).

Side effects can occur on derivatization reactions.  Multiple derivatives can be formed with polyfunctional compounds as a consequence of incomplete derivatization reactions. Uncontrolled formation of unexpected minor derivatives can be produced if the reaction conditions are not well established. Side products of the derivatization reaction can affect the stability of the derivatives formed.

>> The main requirements for a successful derivatization reactions are:

1. a single derivative should be formed for each compound,
2. the derivatization reaction should be simple and rapid, and should occur under mild conditions,
3. the derivative should be formed with a high and reproducible yield and should be stable in reaction medium,
4. in quantitative analysis, the calibration curve should be linier.

>>Main Derivatization Methods

1. Silylation
2. Acylation
3. Alkylation
4. Formation of Cyclic Derivatives
5. Chiral Derivatization

For further explanation of each method of derivatization procedure, I’ll continue to the next post to make it simple to be read ^^