When we wash things down the sink or flush them down the toilet, we don't really think about what happens to all those chemicals and substances. But did you know that they can actually harm our rivers and lakes? That's where chromatography comes in. It's a fancy word for a technique that helps us separate all the different parts of a mixture.

By using chromatography, we can figure out how much of each chemical is in the water, and make sure it's not too much. This is really important because we want to keep our waterways clean and healthy. So, what exactly is chromatography? It's basically a way of separating all the different parts of a mixture so we can see what's in it. We'll go into more detail later on, but basically it works by using different materials to attract different parts of the mixture. Chromatography has been around for a long time, and there are lots of different types. We'll talk about some of them in a bit, but first let's look at how it all started. Overall, chromatography is a really useful tool that helps us keep our waterways clean and safe. It's all about separating mixtures and figuring out what's in them, and we'll explore more about it in the rest of this article.

What is chromatography?

Chromatography is a biophysical technique that separates, identifies, and purifies the components of a mixture for quantitative and qualitative analysis. It can be used to separate a mixture, such as the deep purple ink mentioned in the query, into its individual components, such as blues, reds, yellow, and green pigments. Chromatography can also be used to analyse mixtures, such as identifying active ingredients in a drug or determining the products of a reaction. In the petroleum industry, chromatography is employed to analyze complex mixtures of hydrocarbons. Chromatography is also widely used in biochemical research for the separation and identification of chemical compounds of biological origin.

The method of chromatography

Chromatography is a complex process with a few different types, each with its own unique methods. The process of chromatography involves several steps:

1. Taking a soluble mixture, called the solute.
2. Adding a small amount of the mixture to a stationary phase, which can be a solid, liquid, or gas.
3. Adding a solvent, also known as the mobile phase, to dissolve the mixture and carry it through the stationary phase.
4. Different components of the mixture will travel through the stationary phase at different speeds, causing them to separate into distinct spots or bands that can be viewed on a chromatogram.

One of the simplest forms of chromatography is paper chromatography, which you may have carried out at school. The process involves placing a small amount of the mixture onto a piece of filter paper, which acts as the stationary phase. The paper is then placed in a container with a small amount of solvent, and as the solvent rises up the paper, it carries the mixture with it. Different components of the mixture will travel at different speeds, causing them to separate into distinct spots or bands on the paper.

‍

Chromatography was first invented in 1900 by Mikhail Tsvet, an Italian-Russian botanist who was interested in separating pigments from plant extracts. Tsvet's invention of chromatography was a major breakthrough in the field of analytical chemistry. The word "chromatography" is derived from the Greek words "chroma" meaning "colour" and "graphein" meaning "to write". It is interesting to note that Tsvet's surname means "colour" in Russian, which is quite fitting given his contribution to the field.

Chromatography achieved many of its major breakthroughs in the 1940s and 1950s, thanks to the work of Archer Martin and Richard Synge. They invented a particular type of chromatography known as partition chromatography. This technique involved separating the components of a mixture based on their partitioning between a stationary liquid phase and a mobile liquid phase. This was a significant improvement over earlier chromatography methods, which were often slow and cumbersome.

In recognition of their groundbreaking work, Martin and Synge were awarded the Nobel Prize in Chemistry in 1952. Their invention of partition chromatography was a major milestone in the history of chromatography, and it paved the way for many new applications of the technique in fields such as biochemistry, pharmaceuticals, and environmental science.

Principles of chromatography

We introduced you to some key words up above, in particular stationary phase, mobile phase, and chromatogram. These are some of the basic principles of chromatography. Let's now explore exactly what they mean.

Stationary phase

The stationary phase is a static solid, liquid, or gel. The solvent carries the soluble mixture up the stationary phase. The stationary phase is - as the name suggests - well, stationary. It doesn't move. Examples include paper and silica powder.

Mobile phase

The mobile phase is the solvent used to carry the mixture analysed through the stationary phase. In contrast to the stationary phase, the mobile phase moves. It is a solvent that dissolves the solute you want to analyse or separate, and carries it through the stationary phase.

Chromatograms

Once the chromatography has finished, you'll be left with some evidence of the process. The mixture will have separated out on the stationary phase into different spots or bands. The leftover stationary phase, complete with all of its spots, is called the chromatogram.

A chromatogram is a column or strip of material containing components separated from a mixture by chromatography. It is essentially the output of a chromatography experiment. For example, in paper chromatography, the stationary phase is a sheet of paper. Once you've finished the experiment, the chromatogram is the paper with its final arrangement of different spots.

‍

We'll briefly explore paper chromatography in a bit. However, if you can't wait, check out Paper Chromatography for a more detailed look. Let's focus on two new terms: relative affinity, and retention factor.

Relative affinity

Components within the solute mixture move at different speeds through the stationary phase due to their relative affinities to the two phases. Relative affinity in chromatography refers to how well a component is attracted to either the stationary or mobile phase, which determines how quickly it moves through the stationary phase.

Components that have a stronger affinity to the stationary phase experience a stronger attraction to the static medium and are less soluble in the solvent. This means that they move more slowly through the stationary phase. Conversely, components that have a stronger affinity to the mobile phase are more soluble in the solvent and less attracted to the static medium, so they travel more quickly through the stationary phase.

The differing relative affinities are caused by the attraction to the two phases. For instance, if the stationary phase consists of a polar molecule, it experiences permanent dipole-dipole forces between itself and other polar components in the starting mixture. A nonpolar solvent is typically used as the mobile phase, which means that there are only weak van der Waal forces between the solvent and the components. This results in polar components experiencing a much stronger attraction to the stationary phase than the mobile phase, making them less soluble in the solvent and more attracted to the stationary phase. Therefore, they have a greater affinity to the stationary phase.

Retention factors

As we know, different components travel at different speeds through the stationary phase due to their relative affinities to the two stages, resulting in clear, distinct spots. The distance that each spot travels during a given time period is different, which allows us to calculate retention factors or Rf values.

Rf values are important because they help us to identify components in a mixture. A specific component always produces the same Rf value under the same set of conditions, such as temperature, mobile phase, and stationary phase. If we calculate the Rf value for a particular component, we can compare it to values in a database to determine the identity of the unknown substance.

To calculate the Rf value, we divide the distance travelled by each component by the total distance travelled by the solvent. This provides us with a ratio that we can use to identify components in the mixture.

‍

‍

Correct, components with a greater affinity to the stationary phase move more slowly through the medium, thus traveling less distance in a given time period and having a lower retention factor. Conversely, components with a greater affinity to the mobile phase move more quickly through the medium, traveling further in a given time period and having a higher retention factor. Therefore, the Rf values of different components vary based on their relative affinities to the stationary and mobile phases.

Types of chromatography

It's great to see that you have provided a table comparing different types of chromatography. As you mentioned, there are various types of chromatography, including Thin-Layer Chromatography (TLC), Paper Chromatography, Gas Chromatography, Column Chromatography, Partition Chromatography, and High-Performance Liquid Chromatography (HPLC). Each type of chromatography uses a different stationary and mobile phase, and they have different methods to separate and identify components. However, all these chromatography types operate on the same principles.

TLC uses a plate covered in a thin layer of silica gel as the stationary phase and a liquid solvent as the mobile phase. It is accurate and uses small sample sizes. Paper chromatography, on the other hand, uses a strip of paper as the stationary phase and a liquid solvent as the mobile phase. It is relatively cheap but also uses small sample sizes.

Gas chromatography uses a tube filled with silica powder as the stationary phase and a gaseous solvent as the mobile phase. It requires heating and is highly sensitive. Column chromatography involves a column filled with silica powder as the stationary phase and a liquid solvent as the mobile phase. It is mostly used for separation.

Partition chromatography involves a column filled with a liquid held in place on a solid support as the stationary phase and a liquid solvent as the mobile phase. Separation occurs due to differing solubilities in the two liquids. Finally, HPLC uses a column filled with silica powder as the stationary phase and a liquid solvent as the mobile phase, and it employs pressure to speed up the process.

If you want to learn more about these types of chromatography, you can check out our articles on Thin-Layer Chromatography, Column Chromatography, Gas Chromatography, Paper Chromatography, and Ion Exchange Chromatography.

‍

Chromatography

What is chromatography?

Chromatography is a separation and analytical technique used to split a soluble mixture into its component parts.

What is chromatography used for?

Chromatography has a variety of uses. These include analysing waste water, separating mixtures, purifying compounds and extracting active ingredients from drugs.

How does chromatography work? 

Chromatography has a few basic principles. In chromatography, a solvent, known as the mobile phase, carries a soluble mixture up a static medium, known as the stationary phase. Different components within the mixture have different relative affinities to each of the phases. This causes them to travel through the stationary phase at different speeds and separate out into distinct spots or layers.

What is the basic principle of chromatography? 

In chromatography, different components within the mixture have different affinities to the mobile and stationary phases. This means that some components move faster through the stationary phase than others and causes the components to separate out into distinct spots or layers.

What are the types of chromatography?

There are multiple different types of chromatography. These include TLC, paper chromatography, ion exchange chromatography and column chromatography.

‍