GC/MS Analysis Deconstructed

A scientist conducting GC/MS analysis at Innovatech LabsWhat is GC/MS analysis?

GC/MS analysis is an analytical testing method that combines features of gas chromatography and mass spectrometry to identify different substances within a liquid or volatile sample. GC/MS is commonly used to identify unknown samples, contaminants, or residual solvents. GC/MS analysis is an extremely versatile testing method that can also be used for environmental analysis.

In this blog post, we’ll deconstruct and explore the different testing techniques that can be used as part of GC/MS analysis.

What is Gas Chromatography?

Gas chromatography is the first step of GC/MS analysis. Gas chromatography can also be conducted as a stand-alone test in order to determine the purity of a substance, or to separate different components of a mixture.

In order to conduct gas chromatography, scientists first inject the analyte, a liquid or gaseous sample, into a gas chromatograph (pictured). The gas chromatograph separates the various compounds within the sample by channeling the sample through a narrow tube called a column. The sample is pushed through the column by what’s called a “mobile phase.” The mobile phase is usually an inert gas such as helium or nitrogen. The walls of the column are coated with a “stationary phase.” The stationary phase is a microscopic layer of a polymer. Different compounds within the sample are separated by interacting with the stationary phase and eluting at different times. Scientists can identify each compound within the sample based on its elution time and how it interacts with the stationary phase.

What is Mass Spectrometry?

After undergoing gas chromatography, a GC/MS analysis sample is subjected to mass spectrometry. Mass spectrometry can also be conducted as a stand-alone technique to measure mass-to-charge ratios.

When undergoing mass spectrometry, the sample is injected into a mass spectrometer and bombarded with electrons. The electrons cause some of the sample’s molecules to break into charged fragments, which can be further separated by accelerating them and subjecting them to an electric or magnetic field. The fragmented ions can then be separated according to their mass-to-charge ratio. Scientists can then identify the ions and molecules in the sample by their mass-to-charge ratio and characteristic fragmentation pattern.

Let’s Talk About Headspace Analysis

While GC/MS analysis works well for most samples, additional steps must be taken to analyze the materials outgassed from a sample. Outgassing is the release of a gas that was dissolved, trapped, frozen or absorbed in a sample material.

Headspace analysis is useful for analyzing odors, flavors, residual solvents in pharmaceutical products, and compounds that are given off from a sample during heating. There are two types of headspace analysis which we will explore below.

What is Static Headspace Analysis?

In static headspace analysis, a liquid or solid sample is placed in a vial, sealed and heated to a specific temperature so that the volatile components escape into the headspace above the sample. The headspace gas then undergoes GC/MS analysis in order to identify the components of the off gassed materials. Static headspace analysis is ideal for analyzing volatile compounds such as residual solvents or low molecular weight additives.

What is Dynamic Headspace Analysis?

Similar to static headspace analysis, dynamic headspace analysis begins by heating a sample in order to release volatile components into the headspace of the sample container. In order to increase the volume of the outgassed material, the sample is repeatedly purged and the gasses are flushed out of the sample vessel through a trap for a predetermined amount of time. The trapped headspace gases are then heated and flushed into the gas chromatograph for analysis.

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