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Let’s pretend you walk into a dimly lit room containing approximately a thousand objects. You use this room for both work and relaxation, but it’s so disorganized that you don’t know where your laptop is. Unfortunately, you would have to sort through all the objects in the room until finding what you’re looking for.
That’s chromatography in a nutshell. Since the 1900s, chemists have used chromatography to separate mixtures and identify their components. It’s the only way to get the purest form of a compound, and it’s an essential tool in chemistry.
What’s more, it’s definitely something you’ll need to know if you plan on working in a lab, Read on to find out how chromatography works.
Definition of Chromatography
Chromatography is a laboratory technique used to separate mixtures of compounds.
In its simplest form, chromatography involves the use of a solid support such as paper or silica gel. You’ll also need a liquid solvent such as water or methanol.
The solvent will push through the solid with the help of some external force. Afterward, the components of your mixture will be up for grabs.
Each component will have its own affinity for one material. Heavier molecules will get stuck on parts of the column that are more polar. Lighter molecules won’t interact with those parts much at all.
Components of a Chromatography System
Chromatography doesn’t use a single lab tool. It’s a family of techniques. Each of these techniques uses different components to accomplish the separation process.
A chromatography system consists of three basic parts:
- The column, which holds the sample
- The stationary phase (the material that is coated on a column)
- Mobile phase (the solvent in which you dissolve the sample)
Types of Chromatography
There are five basic types of chromatography, each with its own mechanism for separation. Let’s look at each of these types of chromatography, as well as their uses and applications.
Gas Chromatography
Gas chromatography (GC) is used to separate chemicals based on their volatility. Volatility is a measure of how easily a chemical evaporates. This is important for GC because thermal energy and pressure are used to drive the evaporation process.
You can use gas chromatography to identify unknown compounds. You may also find it helpful for identifying known compounds to determine purity and concentration.
High-Pressure Liquid Chromatography (HPLC)
In HPLC, you pack the stationary phase in HPLC columns. Then, the mobile phase is forced through it by applying high pressure. The pressure required depends on what kind of compound you want to measure and how many are present in your sample.
The mobile phase can be liquid or gas. However, it must be able to flow through the column at a decent speed.
Thin Layer Chromatography (TLC)
Thin layer chromatography (TLC) is a simple and inexpensive method for chemical analysis. You can use it to analyze almost anything, including:
- Steroids
- Carbs
- Nucleotides
- Glycosides
- Lipids
- Fatty acids
- Alkaloids
The thin layer of adsorbent material in TLC is usually foil. You must place this adsorbent material on a plate. Then, apply the sample to the top using drops.
The solvent (or mobile phase) will be in a closed chamber with the plate. The solvent will then move up through the plate. During this movement, the solvent will carry along compounds that have different affinities for different parts of the stationary.
Paper Chromatography (PC)
Paper chromatography is a separation of mixtures using paper. You’ll soak the paper in one liquid and use this as the stationary phase. Another liquid will flow through the paper to help with the separation process.
When dried, components of a mixture separate out to form spots on the paper’s surface.
You can do this with any type of paper, but most people use filter paper. If filter paper is your preferred medium, soak it in an organic solvent like methanol or ethanol.
Column Chromatography
Column chromatography is a type of liquid chromatography that uses a glass column. This tube is filled with a porous material as the stationary phase. A liquid solvent will be the mobile phase.
You can use column chromatography to separate molecules based on their size or charge. It’s similar to TLC, however, this process takes much longer. Still, it can give better results than TLC, depending on the substance.
The Advantages of Chromatography
You can use chromatography to separate mixtures of compounds that are too complex to analyze in any other way. You can also use it to determine the purity of a substance and its components. And, it’s useful in identifying the structure of unknown compounds.
Another benefit is that it’s an extremely precise method of separating compounds. It even works well on compounds with very similar physical properties. For example, you can use paper chromatography to separate the chemicals in different water color markers.
You can also use chromatography to determine the amounts of each compound present in a mixture. It helps you ensure that the solution is exactly what it says it is.
Finally, chromatography is one of those lab techniques that almost anyone can do. You don’t need a lot of fancy equipment or extensive training to run a simple paper chromatography experiment. All you need is some dye, water, and filter paper.
Expand Your Knowledge of Lab Techniques
Chromatography is an important tool in chemistry and biology, so understanding how it works can help you out in many situations. Use it to identify chemical compounds in your food, or even household items like pens. The more you know about how chromatography works, the better equipped you’ll be to use it in your classroom.
If chromatography has piqued your interest, check out some of the other lab techniques we’ve discussed in our science section. You’ll find a lot of great ideas for activities to do in your classroom or at home.