Unlike other methods, the mobile phase in GC does not interact with chemicals and only serves to carry them. It moves through the column at a constant flow rate and exits at the detector outlet. The carrier gas is introduced from a gas cylinder into the gas chromatograph. The stationary phase is assembled as a compacted material (packed column) or as a wall-coating film (capillary column). This can be a number of different materials with varying polarities, either solid or liquid that interact with the chemicals passing through. Inside of the tube is the stationary phase. The column is a coiled tube made of metal or glass material that can withstand high temperatures and vary in length or diameter. This is where all the action (a.k.a separation of compounds) takes place. It is also possible to analyze gas samples (air, breath) and injection is usually through a gas valve. It may be a single substance or a mixture, liquid or solid that is dissolved in solvent and only a tiny amount (few microliters) is injected via syringe. Typically, GC samples consist of non-polar, low molecular weight, thermally stable, and vaporizable chemical material. The type of sample can vary greatly depending on the study. GC Components: A Closer Look Sample Injection It is because of this principle that GC has its usefulness. To put into context, you can imagine that a compound that is “held up” by the stationary phase will have a longer tR than another that is traveling freely with the mobile phase. Therefore, it is expected that a sample containing multiple substances will result in different retention times (each substance with its own tR). The time that a compound spends interacting with the stationary phase will depend on the compound’s unique composition. This happens because a compound can be either moving along with the carrier gas or spend some time attached to the stationary phase. If you inject a mixture, the components will separate as they travel at different speeds. The gaseous molecules are then mixed with the mobile phase, which is also known as the carrier gas, because it does exactly that: it carries the sample through the column. How GC Worksīecause the injector port is contained in an oven (see Figure 1), once you inject your sample it will be immediately vaporized (poof!). Figure 1 shows the basic components that make up a GC system.įigure 1. This measure of time is called retention time (tR) and is determined by the detector when a compound exits the column. The nature of this partitioning will dictate how much time a specific compound spends in the column until it eventually reaches the detector. After this, your material of interest will take a steamy journey through a column, where it is partitioned between a mobile phase and a stationary phase. Instead, the gas chromatograph will vaporize it for you. This doesn’t mean that your sample has to be a gas (although it could). When it comes to GC, the compounds that are analyzed are in, not surprisingly, the gas phase. If you are familiar with other chromatography methods, such as HPLC or GPC, then you already know more than you think! You may already know that chromatography covers a wide range of analytical techniques that are used to separate, identify, and quantify compounds. If you are hesitant because you know little about GC, then this article will help you with that. Maybe you found a paper in which they used gas chromatography (GC) to analyze a sample that is similar to yours and now you are wondering if you should try it too.