Lab Report Gas Chromatography

Gas chromatography (GC) is a chromatography technique where the separation of individual components (called analytes) from a sample relies on their differing distribution between the mobile phase and a stationary phase. The mobile phase is what carries the analyte (components being analysed) through the stationary phase and in GC, it is an inert gas, (usually helium or nitrogen). The gas must be inert so it will not react with the samples to give a false reading. The stationary phase is the substance that is fixed in place during chromatography to which the sample adsorbs. GC can have two types of columns, capillary or stacked. In capillary columns, the stationary phase is a thin layer of non-volatile liquid or polymer with a high boiling point …show more content…
This is due to the intermolecular forces that exists between the molecules, the molecular weight of the molecule, the geometry of the molecule, and the polar/non polar nature of the molecule. The three forces that exist between molecules (intermolecular forces) are dispersion forces, dipole-dipole forces, and hydrogen bonds. Dispersion forces arise from the random motions of electrons within a molecule. The fluctuations in electron density causes a temporary partial negative charge (dipole) and can repel electrons from a nearby molecule, inducing a partial positive charge. These two temporary dipoles are electrostatically attracted to each other but these dipoles are only temporary and are the weakest of the the intermolecular forces. These forces occur in every atom and molecule because of the random motions of electrons. Dipole-dipole forces is when a molecule has a permanent partial charge on its poles because of an atom covalently bonding to another atom with a different electronegativity, causing electrons to spend more time in one area than the atom with the lower electronegativity. These are stronger than dispersion forces because of the permanent dipoles. There is also asymmetry in the molecule that makes the molecule polar. Hydrogen bonding is an extreme form of dipole-dipole forces where hydrogen covalently bonds to a highly electronegative atom (nitrogen, oxygen, or fluorine). This causes an uneven sharing of electrons and creates a higher partial charge than in dipole-dipole forces. Usually, a molecule with a higher molecular weight will also have more electrons, giving it stronger dispersion forces (compared to molecules with less electrons). Two isoelectric (molecules with the same number of electrons) molecules can have intermolecular forces of different strengths. A