How to Understand the Difference Between HPLC and GC?

Table of contents

• Introduction and Background
• HPLC & GC
• Applications of HPLC
• Applications of GC
• Difference between HPLC and GC
• Case studies
• Conclusion

Introduction and Background

High-pressure liquid chromatography (HPLC) and Gas chromatography are highly used instruments in the Pharmaceutical industries. Now the question is what is the difference between HPLC and GC? Most of the chemists have a lot of confusion related to their use which is why I decided to share my skill-based knowledge on this topic. This article will clear all your doubts related to the difference between HPLC and GC and you can easily select the suitable instrument during the method development. Having read this article you will be able to answer several questions related to this topic; such as:

• What is HPLC?
• What is GC?
• For which type of molecules GC should be used?
• For which type of molecules HPLC should be used?
• What is the differance between HPLC and GC?
• What are the limitations of GC and HPLC?
• What are the different components of HPLC?
• What are the different components of GC?
• Can HPLC be used in place of GC?
• Can GC be used in place of HPLC?

HPLC & GC

HPLC

High-pressure liquid chromatography is a separation technique based on solid stationary phase and liquid mobile phase and separations are achieved by partition, adsorption or ion exchange processes depending upon the type of stationary phase used. The following are the different components of HPLC:

• Mobile phase
• Degasser
• Pump
• Mixing valve
• Guard column
• Sample injection port
• Injector
• Column
• Column temperature controller
• Detector waste collector
• Data processor &
• Chromatogram

Applications of HPLC

HPLC is Quantitative and Qualitative analysis

• Pharmaceuticals
• Testing laboratory
• Research centres
• Biotech industries
• Pesticide industries

GC

GC (Gas chromatography) is a chromatographic technique for the separation of volatile components. In GC components to be separated are distributed between two phases, one of them is stationary phase and the other is mobile phase is gas which moves percolating through the stationary phase. The chromatographic process occurs as a result of repeated sorption-desorption acts during the movement of the sample components along the stationary phase and the separation is due to differences in the distribution coefficient of the sample components. The following are the different components of GC:

• Carrier gas ( Generally Helium and Nitrogen are used)
• Flow control valve
• Sample injection port
• GC column (Now a days only capillary columns are used)
• Column oven temperature controller
• Detector
• Outlet
• Data processor &
• Chromatogram

Applications of GC

Qualitative and Quantitative analysis of volatile molecules in:

• Pharmaceuticals
• Air pollution
• Foods
• Pesticides residues
• Petroleum industries
• Essential oils
• Testing laboratory

Differences between HPLC and GC

Case studies

Analysis of para chloro nitro benzene, Toluene and cyclohexane

1-chloro-4-nitrobenzene

It has very good UV absorption and hence it can be analysed by HPLC. Due to high V.P, it can not be analysed by GC

Toluene

It has UV absorption and it is a volatile molecule with oxidisable carbon atoms. Hence it can be analysed on GC using an FID detector as well as HPLC using a UV detector.

Cyclohexane

It has no UV absorption and hence it can not analysed on HPLC using a UV detector. It is a volatile molecule with an oxidisable carbon atom and hence it can be analysed on GC using an FID detector.

Conclusion

Both HPLC and GC are important instruments for any pharmaceutical industry. Now I can hope that all your doubts related to the selection of instruments have been cleared. For any question related to this blog write in the comment section and I will answer on a priority basis.

References

• IP
• USP

Abbreviations

• FID: Flame ionisation detector
• GC: Gas chromatography
• HPLC: High – pressure liquid chromatography
• ELSD: Evaporation light scattering detector
• FD: Flurorance detector
• ECD: Electrochemical detector
• ECD: Electron capture detector
• BP: Boiling point