Dr. Ram Speaks Gas Chromatography—From Injection to Detection: Part 1

October 19, 2017 Science Unfiltered

Guest Author: Ramkumar Dhandapani, Ph.D.

Hello everyone! I am Dr. Ramkumar Dhandapani, your Gas Chromatography (GC) Guide, taking you from injection to detection.

With a Ph.D. in Analytical Chemistry from Seton Hall University, 14 years of hands-on experience, and the GC Technical Manager at Phenomenex, it may come as no surprise that I am exceptionally passionate about GC separation. That is why I am excited to bring this new article series to life, “Dr. Ram Speaks GC, From Injection to Detection.” This series will help build a stronger understanding of GC as we explore various concepts and applications. You can expect to find answers and discussion on the following topics:

Understanding basic concepts in GC
Provide systematic ways to troubleshooting problems
Choosing the right GC column for your application
Understanding common GC myths
Explore proved tips and tricks

Let’s start the journey the best way possible—the basics. The main components of a GC system are shown in figure below, which include:

Carrier Gas
Gas traps
Autosampler
GC column
Oven
Detector

Breakdown of the GC Instrument:

Carrier Gas: The carrier gas serves as the mobile phase. It is important that the carrier gas is of high purity, very inert, and suitable for the detector. Helium, nitrogen, and hydrogen are the common carrier gas choices.
Gas Traps: Scrubbing system that traps even ppm level of hydrocarbons, moisture, and oxygen and can extend a GC column’s lifetime.
Autosampler: Injects samples sequentially into the GC system through the inlet.
Inlet: Introduces sample into the GC system. Cool on column, split, splitless, and PTV (programmed temperature vaporization) are some of the inlet systems.
GC column: This is considered the heart of GC, where the separation of analytes takes place. Shown below is a cross section of Zebron™ GC WCOT (wall coated open tubular) column, which has 3 distinct regions:

Polyimide
Fused Silica
Stationary Phase

All 3 layers are exceptionally important to develop a decent GC method. The outer polyimide coating gives flexibility to the column and extends its temperature limit. The purity of fused silica helps to attain symmetric peaks for active analytes, and the inner layer of stationary phase helps to separate analytes. In GC, separation is primarily based on boiling point (Van der Waals interaction) although other intermolecular interactions can have an influence on the selectivity.

Oven: This controls the temperature and helps to manipulate the retention of analytes. The oven can be operated in isothermal mode, temperature ramp, or a combination of both isothermal and ramp called programmed temperature GC.
Detector: Helps to detect the analytes that come out of the GC column. Flame ionization detector, thermal conductor, electron capture, and mass spec are some of the most common GC detectors.

Stay tuned for the next article in “Dr. Ram Speaks GC, From Injection to Detection”, where we talk about steps that need to be considered before buying a GC column.

Good Luck!