Page 9 - Fundamental Guide to GCMS
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Chapter 1  Basics of GC




            Introduction






                Chromatography is a technique that separates complex   Principles and Applications
            mixtures into its individual components for identification   GC is also known as gas-solid or gas-liquid partition
            and quantification. It was first developed in the early 1900s   chromatography due to the distribution of compounds between
            by Russian botanist, Mikhail S. Tswett. He demonstrated   the solid/liquid stationary phase in a column and the gaseous
            the separation of colored plant pigments and termed this   mobile phase.  Figure 1 illustrates the separation of compounds
            technique “chromatography”. It was not until several decades   in a GC. The sample mixture is injected, vaporized, and flows
            later, around 1930s, where this technique sparked off further   into the thermally-controlled column by an inert gas. The
            developments.                                      sample compounds can interact with the stationary phase
                Scientist Archer J. P. Martin, who worked on paper   through various intermolecular forces such as Van der Waals
            partition chromatography, went on to develop Gas   forces and dipole-dipole interactions. Some compounds tend to
            Chromatography (GC) with fellow scientist Anthony T. James.   interact more strongly due to their polarity, thereby resulting
            Their invention on GC was awarded the Nobel Prize in Chemistry   in a higher concentration in the stationary phase compared to
            in 1952 and it set the stage for many other developments such   the mobile phase (i.e. higher partition coefficient, Equation
            as Liquid Chromatography (LC) and Gas Chromatography Mass   1). As a result, these compounds are strongly retained in the
            Spectrometry (GCMS).                               column and have longer retention time (RT) compared to
              Figure 2: Principles of GC                       compounds of weaker interactions with the stationary phase.
                GC is a technique that vaporizes the sample mixture into
            gaseous compounds and separates them based on the boiling   As time passes, with continual flow of inert gas and a thermally-
              2019/11/27 ver.
            point of the compounds and their differential adsorption on   controlled column, the variations in the partition coefficients
            a porous solid or liquid support. It is commonly used for the   of the compounds (Equation 1) result in the separation of
            analysis of low molecular weight and volatile compounds and is   the compounds in a mixture. The separated compounds
            widely applicable in many industries such as in forensic science,   subsequently elute from the column and gets detected.
            food, environmental testing, pharmaceuticals, petrochemical,
            pesticides and fragrances. The following sections in this chapter
            details the separation principle and basic instrumentation of GC.  At the early forefront of GC development, Shimadzu
                                                                 embarked on this technology and developed the first GC
                                                                 in Japan in 1956. Subsequently, we developed newer and
                                                                 improved versions of GC and GCMS and achieved several
                                                                 key milestones. Click to learn more.  Click here




                                     Liquid or Solid Stationary   Separated Compounds of
                                        Phase in Column          Sample Mixture






              Inert Gas Flow  He Carrier Gas                 He Carrier Gas
              (Mobile Phase)                                                                  B    A


                                                                                       0        Time
                                       Immediately after injection  After several minutes  Resulting chromatogram

                            Sample Mixture

            Figure 1. GC separation principle. The compound in red have a stronger interaction with the stationary phase and gets retained longer in the column. This results in the
            separation of the mixture where the red compound has a longer retention time than the blue compound (RTred > RTblue).



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