Difference between HPLC and GC Technique

HPLC (high-performance liquid chromatography) and GC (gas chromatography) are widely used separation techniques in pharmaceutical industries, industrial laboratories, and academia. High-performance liquid chromatography has applications in the field of pharmaceuticals, polymers; life sciences, etc. Gas chromatography has applications in pharmaceuticals, petroleum, petrochemical industry, etc.

HPLC and GC operate on the same principle but with different results. In general, chromatography is the process of separating parts of a mixture by passing it through a gaseous column or liquid solution and generating data for the scientist to analyze.

HPLC and GC are used in analytical chemistry to analyze samples and determine what the sample contains, its techniques are effective for the separation of analytes and it is a multipurpose and very well-accepted chromatographic technique utilized for the separation of complex mixtures. HPLC and GC are chromatography techniques based on the physical state of the mobile phase. HPLC uses liquid as the carrier and GC uses gas as the carrier.

HPLC and GC techniques are used for identification and quantification purposes but for different intents as their functions and applications are different further HPLC and GC are based on the principle where the compound is subjected to the surface or within a solid or liquid stationary phase by isolating it with the help of the mobile phase. The selection of instruments is purely based on the nature of the sample and the requirement of the sample.

The following table summarizes the differences between HPLC and GC techniques:

	HPLC	GC
Principal	Separation of the sample is accomplished by the solid stationary phase and liquid mobile phase.	Separation of the sample is accomplished by liquid or solid stationary phase and gaseous mobile phase.
Temperature Control	Temp. the control approach is not necessary or required. Generally ambient temp. is required.	Temp. control is much more important as the column is placed inside the oven with a control temperature program. Generally, higher temperatures are required for analysis.
Sample State	Separation of the liquid state of any soluble samples usually with higher molecular weight.	Separation of volatile and thermally stable samples with low molecular weight.
Column	Columns are generally shorter and broader in diameter.	Columns are long, normally 10 to 60 meters in length, and narrow in diameter.
Column Types	Octadecylsilane, Octyl silane, Hexyl, Trimethyl Silyl, Amino, Cyano, TMS, Silica, Hillic, Diol, Ion exchange, Chiral, Phenyl, Gel permeation & Size exclusion chromatography	WCOT, SCOT, PLOT, Carbowax, Polyethylene glycol, Dimethylpolysiloxane, Phenyl methyl polysiloxane, High molecular mass esters, Amides, Hydrocarbons, Polyaromatic compound, Cyanopropyl polysiloxane
Separation	Separation is based on the interaction of samples with mobile and stationary phases.	Separation is based on the boiling point of the sample.
Resolution Issues	Samples with identical polarity	Samples with a similar molecular weight
Mobile Phase	Liquids, e.g. Polar solvents like water, acetonitrile, methanol, etc. Nonpolar solvents like Hexane, Heptane, isopropyl alcohol, dichloromethane, etc.	Gases, e.g. Nitrogen, Helium, Argon, Hydrogen, Oxygen
Speed	Analysis speed is slow.	Analysis speed is fast
Peak shape	Generally, detect bigger or wider peaks that affect lower resolution.	Relatively sharp peaks were observed with good resolution.
Detectors	UV-Visible detector, Photodiode-array detection, Refractive index detector, light scattering detector, Charged aerosol detector, Conductivity detector, Fluorescence detector, Chemiluminescence detector, Optical rotation detector, Mass spectrometric, IR Detector, etc.	GC detectors are sensitive and selective, e.g. Flame ionization detector (FID), Thermal conductivity detector (TCD), Electrochemical detector, Electron capture detector, Nitrogen phosphorous detector, Flame photometric detector, Electrolytic conductivity detector, Mass spectrometric, Photo Ionization detector, Reduction gas detector, Catalytic combustion detector, Helium ionization detector, etc.
Cost	Less costly	High cost

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FAQ’s

References:

1. Blumberg LM. Theory of Gas Chromatography. In: Poole CF, editor. Gas Chromatography, First Edition. Elsevier,
2. Laird CK. Chemical Analysis: Gas Analysis. In: Walt Boyes, editor. Instrumentation Reference Book. Butterworth-Heinemann,
3. “High-Performance Liquid Chromatography.” Wikipedia, Wikimedia Foundation, “Gas Chromatography.” Wikipedia, Wikimedia Foundation.
4. Ahuja S (1976) Derivatization in gas chromatography. J Pharm Science,
5. Hartmann CH (1971) Gas chromatography detectors. Analytical Chemistry,
6. La Course WR (2002) Column liquid chromatography: equipment and instrumentation, Analytical Chemistry.