Chromatography: Types And Principles Of Work
Introduction And Abstract
(# Chroma = Colour, # Graphy = Grafein (in Greek) = To write). Chromatography is a method used to separate components of a mixture and they undergo two phases, the stationary and mobile phase. The stationary phase is responsible for solids and the mobile phase is responsible for liquids and gases as the mobile phase flows through the stationary phase and carries the components of the mixture with it. In 1900, a Russian botanist invented the first chromatography technique while he was undergoing his chlorophyll research. Chromatography isn’t only used to separate organic and inorganic compounds, but is also used to examine the components of a mixture and their relation with one another. Also, chromatography completely isolates the components which will help when wanting to look for further information on a component. In addition, chromatography is often used in our daily lives like:
- Pharmaceutical companies: to determine the quantity of a chemical in new products
- Hospitals: to determine alcohol levels in a patient blood stream
- Law enforcement: to compare samples found in crime scenes
- Environmental agencies: determine the percentage of pollution in water or to purify chemicals
On the other hand, this technique has some disadvantages such as:
- Less accurate compared to other scientific techniques
- Laboratory tools are costly
- Consumes a lot of time
Jim Clark, J. 2007. Thin-layer chromatography. [Online]. [8 January 2020]. Available from: https://www.chemguide.co.uk/analysis/chromatography/thinlayer.html
Types of Chromatography
- Liquid chromatography – used to check pollution percentages by testing liqui samples
- Gas chromatography – used in forensics to analyze fibers found in crime scenes as well as in airports to detect bombs, alcohol, weapons, or drugs
- Thin-layer chromatography – used in forensics to analyze the dye composition in the fibers and to detect residue in food
- Paper chromatography – used to separate color substances and distinguish their solubility
How does Chromatography work?
All 4 types of chromatography have to go through the mobile phase and the stationary phase. The stationary phase is stable “doesn’t move” while the mobile phase moves through the stationary phase to start testing. The mobile phase stops moving when all the components are absorbed
Calculation:
To calculate chromatography, we need to calculate the retention factor (RF). The retention factor is the total distance the components have travelled in a solvent.
Chromatography. c2019. Chromatography. [Online]. [5 January 2020]. Available from: https://en.wikipedia.org/wiki/Chromatography
Experimental research
Many experiments are done using this technique but in this research, we will use an experiment which asks: “Which substance (iron or copper) is more soluble (dissolves faster) in the mobile phase” -PAPER CHROMATOGRAPHY- with a claim that says: Copper is more soluble in the mobile phase.
Materials
Gloves, facemasks, a beaker, filtered paper, Ammonia (NH3), Iron (Fe), Copper (Cu), droplets, ruler, scissors, pencil.
Procedure
- We drew two parallel lines on separate sides of the filtered paper then drew a horizontal line to represent the starting point.
- We marked two points on the starting line.
- We cut the paper from the parallel lines to obtain a rectangular shaped strip.
- Using the droplet, we dropped Cu (blue) on one of the two points on the starting line, then dropped Fe (brown) on the other point while holding the filtered paper vertically.
- With the help of our teacher, we dipped the filtered paper in NH3 for 5 seconds.
- Then we placed it vertically in an empty beaker and waited for a while to observe which element would move faster.
- After waiting, we used a ruler to measure the total distance (traveled by mobile) obtained from the starting line until the finish line (where the ammonia stops).
- Then we measured the distance (from start to circle-centre) travelled by each component separately. (each copper and iron circle)
- We measured retention time of each solute, which measures the speed at which a substance moves in a chromatographic system, by dividing the total distance moved by each solute separately over the total distance travelled by the solvent from the origin.
- We recorded our obtained data and cleaned up our work space.
Bheem, B. 2019. Paper chromatography. [Online]. [8 January 2020]. Available from: https://owlcation.com/stem/What-is-Paper-Chromatography-
Results
Data obtained
- Distance to solvent front
- 3.5cm
- Distance to center of ring front Fe3+
- 0.5cm
- Rf of Fe3+
- 0.14cm
- Distance to center of ring front Cu2+
- 2.8cm
- Rf of Cu2+
- 0.8cm
- Distance to solvent front
- 3.5cm
- Mobile Phase
- Stationary Phase
- Fe – insoluble
- Fe – soluble
- Cu – soluble
- Cu- insoluble
The stationary phase is the water trapped between the cellulose fiber of paper while mobile phase is a developing solution that travels up the stationary phase carrying samples with it.
John matsen, J. 1965. Chemical Reactions in Chromatographic Columns. [Online]. [8 January 2020]. Available from: https://doi.org/10.1021/j100886a027
Conclusion / Discussion
Overall, the experiment succeeded in showing that our hypothesis or claim regarding Copper (Cu) being more soluble in the mobile phase. Evidence that support our claim include the calculations of the retention factor (Rf) which is the ratio between the distance travelled by a substance through the stationary phase relative to the distance travelled by the mobile phase at the same time and under certain conditions. As shown in our obtained data, we calculated the (Rf) of Fe which was: 0.14, then we calculated the (Rf) of Cu which was: 0.8. Thus, we concluded that Cu traveled at a faster rate than Fe did. The reasoning behind it is that copper is indeed more soluble in the mobile phase than the stationary phase as the analyte is the substance which is to be purified or isolated during chromatography, in this case it was Cu and Fe. The mobile phase is the solvent which carries the analyte and travels through the stationary phase, which is the substance which is fixed in place for the chromatography procedure and is the phase to which solvent and the analyte travels through or binds to it. Iron and Copper were subjected to flow by mobile liquid onto or through the stable stationary phase. The stationary phase doesn’t move while the mobile phase does move through the stationary phase and carries the components of the mixture. The components (Cu and Fe) have different rates of migration which provides the separation of the components. The stationary phase retards the movement of the components in the mixture, thus if the adsorption is very strong then the rate of movement is very low. In other words, If the Solubility increases in the mobile phase, then the Solubility or Adsorption decreases to the stationary phase. In Adsorption the chemical components attach (stick) to the outer surface of the particle, while in Absorption the chemical components incorporate (enter) into the particle’s structure. Because Copper had a high rate of movement (Rf), it’s more soluble in the mobile phase and less soluble or weakly absorbed in the stationary phase. Another reasoning shows that in normal-phase chromatography, the stationary phase is polar, and the mobile phase is nonpolar. Non-polar molecules will travel farther than polar molecules because they have little attraction and so will spend most of their time dissolved in the moving solvent. Copper is a single element, so it is nonpolar which means it’ll travel farther (2.8 cm) than polar molecules (Fe) which travelled only 0.5cm because polar molecules spend more time dissolved in the stationary phase and less time in the mobile phase, they aren’t going to travel very fast up the paper.
- Calvin Giddings and Roy Keller, J.A.N.D.R. 2016. chromatography. [Online]. [8 January 2020]. Available from: https://www.britannica.com/science/chromatography
- Chromatography. c2019. Chromatography. [Online]. [5 January 2020]. Available from: https://en.wikipedia.org/wiki/Chromatography
- Quora, T. 2018. What are the disadvantages of chromatography Quora? [Online]. [5 January 2020]. Available from: https://www.quora.com/What-are-the-disadvantages-of-chromatography
- John Madsen, J. 1965. Chemical Reactions in Chromatographic Columns. [Online]. [8 January 2020]. Available from: https://doi.org/10.1021/j100886a027
- Jim Clark, J. 2007. Thin-layer chromatography. [Online]. [8 January 2020]. Available from: https://www.chemguide.co.uk/analysis/chromatography/thinlayer.html Go back and edit info
- Calvin Giddings and Roy Keller, J.A.N.D.R. 2016. chromatography. [Online]. [8 January 2020]. Available from: https://www.britannica.com/science/chromatography
- Bheem, B. 2019. Paper chromatography. [Online]. [8 January 2020]. Available from: https://owlcation.com/stem/What-is-Paper-Chromatography-Principle-Uses-experiment-video
