Everything You Need To Know About Chromatography for the USABO, Part 2: Paper, Size Exclusion, Ion Exchange, and High-Performance Liquid Chromatography
Creds @ChessFun for suggesting paper chromatography lol
Last week’s article went over column and affinity chromatography. Let’s go over some other kinds of chromatography.
First, paper chromatography. In this case, the stationary phase is the paper, which is made of polar cellulose fibers that can conduct substances upwards via capillary action. Polar compounds will be slowed by their interactions with the polar cellulose, while nonpolar molecules will move through quickly and travel farther in a given time period. Polarity can be quantified using an Rf (retention factor) value, which is the ratio of the distance traveled by the compound over the distance traveled by the solvent. The higher the Rf value of a compound, the less polar it is.
Second, size exclusion chromatography (SEC). SEC separates molecules by size. Smaller molecules are trapped in a maze, and large molecules quickly and easily pass through. Larger molecules elute first, and smaller ones elute last. Each maze is in a single bead, and these beads put together create the gel as a whole. Below is an image showing this.
Third, ion exchange chromatography. This is basically the exact same thing as column chromatography, except the stationary phase and mobile phase are different charges instead of different polarities. Anion exchange chromatography isolates anionic substances from the sample, so the stationary phase is positively charged.
Elution occurs by one of two methods. The first option is straightforward: we can use a salt solution to introduce competitive cations. These cations will compete with the positively-charged stationary phase to bind the anions of interest, allowing them to fall freely into the collection tube. Another method for elution is to increase the pH of the solution flowed through to a value above the pI of the stationary phase. This will deprotonate it and the stationary phase will no longer be positively charged, so it wont have an affinity for the anions of interest anymore.
For cation exchange chromatography, the stationary phase is negative. We are trying to isolate cations of interest from the sample. Elution occurs via competitive anions or a low-pH solution.
High-performance liquid chromatography is basically an upgraded version of all the chromatography techniques discussed thus far that involve a column. High-pressure pumps are used to make things faster.
So yeah! That’s chromatography!! Also str3am 2093! WE #1 ON APPLE MUSIC BB!
thing: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5206469/
