News > An Overview of How Gas Chromatography Processes are Validated and Optimised

An overview of how gas chromatography processes are validated and optimised.

Gas chromatography (GC) is undoubtedly one of the key analytical techniques used to separate and  interpret chemical components in a mixture.

A simple explanation of how gas chromatography works?

Gas chromatography is the process of separating compounds in a mixture by injecting a gaseous or liquid sample into a mobile phase. The sample is first injected into the inlet of the GC, where a steady flow of an inert “carrier gas” is used to move it through a packed column. As the sample passes through the column, the various components interact with the column material. Each component elutes at a different rate, depending on how strongly it interacts with the column. The outlet of the column feeds directly into a detector that characterizes the eluted compounds based on column retention time and signal strength. Eventually, the sample and carrier gas are vented out as waste.

Maintaining constant carrier gas flow

Most experts will agree that it is critical the GC outputs accurate, repeatable results to ensure differences between two sample injections are only due to differences in chemical composition.  Consequently, it is imperative to keep the flow rate of the carrier gas constant, as deviations disrupt the detection of chemical compounds.

It is easy to conclude that fast, precise, highly accurate mass flow controllers that can be used to deliver exacting inert gas flows to your GC column are needed. When these mass flow controllers are used, they provide valuable benefits to GC applications: Stable, low-flow control: Even in low flow conditions, mass flow controllers provide stable flow from zero to full scale within tens of milliseconds.

• Versatile gas compatibility: One controller can measure 98+ gasesand custom gas blends, including common inert gases like N₂, He, Ar, and CO₂.

• Easy to integrate & use: Most devices come standard with 6-button backlit displays for easy control, or you can connect via a variety of industrial communication protocols.

How to maintain stable pressure control with fixed orifices

Flow-control valves include simple orifices to sophisticated closed-loop electrohydraulic valves that automatically adjust to variations in pressure and temperature. Gas chromatographs with fixed orifice valves require stable pressure control. A common solution is the OEM pressure controller (EPC-Series), which provide numerous benefits to GC applications, including:

• Compact & easy to integrate: These compact controllers are easy to integrate into pre-existing setups, and can be customized to almost any flow rate, pressure condition, or speed required for GC applications.
• High quantity: These are a good option for high volume OEM applications, as they are sold in batches of 25 or more units.
• Fast, versatile control: An EPC can be configured with either single proportional valves, dual proportional valves, or to control back-pressure with control response times to 50 ms.

As we all know, in gas chromatography applications, a single valve EPC is ideal for regulating straightforward applications such as using a pressure regulator to knock down inlet pressure off a gas bottle, providing volumetric flow control against a calibrated orifice, or controlling stability in any desktop analyzer, lab in a box, reactor, or sample preparer.

Authenticating gas chromatograph operation in-house

A portable mass flow meter is an accurate and versatile device that can verify the performance of a GC, such as the flow rate of the carrier gas. This flow rate in the gas chromatograph is essential to the performance accuracy of the instrument.  It is often used to check mass flow, pressure, and volume measurement on the input and vent of the GC.

These meters offer numerous benefits including:

• Fast, accurate, & repeatable: NIST-traceable accuracy of ±0.5% of reading or ±0.1% of full scale with <10 ms response times and a repeatability of ±(0.1% of reading + 0.02% of full scale).
• Highly versatile measurement: One device can verify both pressure and flow of 98+ gases across a wide 10,000:1 operating range to cover both capillary and carrier gas flows.
• Easy integration into existing setups: RS-232 serial communications for data logging to any PC, PDA, or other device with serial terminal capability

In conclusion, successful GC evaluation and optimization requires versatile measurement, accuracy and repeatability, stable low-flow control and high-quality performance. Contact one of our team so they can walk you through the best options for your process.