What Are the Advantages of HPLC Over GC?

••• PhotoObjects.net/PhotoObjects.net/Getty Images

Chromatographic techniques are performed in scientific laboratories to separate chemical compounds from an unknown sample. The sample is dissolved in a solvent and flows through a column, in which it is separated by the attraction of the compound against the material of the column. This polar and non-polar attraction to the column material is the active force that causes the compounds to separate over time. The two types of chromatography used today are gas chromatography (GC) and high performance liquid chromatography (HPLC).

Mobile Carrier Phase

Gas chromatography vaporizes the sample and it is carried along the system by an inert gas such as helium. Using hydrogen produces better separation and efficiency, but many laboratories prohibit the use of this gas due to its flammable nature. When using liquid chromatography, the sample remains in its liquid state and is pushed through the column under high pressures by various solvents such as water, methanol or acetonitrile. Different concentrations of each solvent will affect the chromatography of each compound differently. Having the sample remain in its liquid state increases the stability of the compound.

Column Types

Gas chromatography columns have a very small internal diameter and their length can range from 10 to 45 meters. These silica-based columns are coiled along a circular metal frame and heated to a temperature of 250 degrees Fahrenheit. Liquid chromatography columns are also silica-based but have a thick metal casing to withstand high amounts of internal pressure. These columns operate under room temperature and range from 50 to 250 centimeters in length.

Compound Stability

In gas chromatography, the sample injected into the system is vaporized at about 400 degrees Fahrenheit before it is carried through the column. Thus, the compound must be able to withstand heat at high temperatures without breaking down or degrading into another molecule. Liquid chromatographic systems allow the scientist to analyze larger and less stable compounds because the sample is not subjected to heat.

Related Articles

The Differences Between HPLC & GC
How to Read a Gas Chromatograph
Basic Components of an HPLC
What Is the Fractional Distillation of Air?
How to Calculate HPLC Resolutions
Steam Distillation vs. Simple Distillation
How to Build a Fractional Distillation Column
What Are the Disadvantages of HPLC?
What Is Vacuum Pump Oil?
How to Explain Simple Vs. Fractional Distillation
How to Separate Oxygen From Liquid Air
Volume Vs. Mass Density
Disadvantages & Advantages of an HPLC
How to Improve Fractional Distillation
How to Calculate Kovats Index
How to Calculate RRT
The Types of Electrophoresis
What Does the Latent Heat of Vaporization Measure?