Recently, I have been using a machine called a HPLC quite a lot in my research. This has lead to quite a lot of questions like, “What is an HPLC? What does it actually do?” mostly asked by my grandma.
So, HPLC stands for High-Performance Liquid Chromatography, which is a mouthful. One will also hear it referred to by an older term, High Pressure Liquid Chromatography. You can see why most scientists are lazy and just refer to it as HPLC.
What a HPLC actually does is force a liquid mixture, which you want separated, through a tube of packed beads (called a column) at high pressure. In this liquid mixture there is some component that you want to separate from the rest of the mixture, whether it is a protein you need purified after synthesis or a drug from a urine sample. This is how doctors monitor that you are getting the right dosage of a drug and one of the ways that cocaine and other illicit drugs are tested for1.
As the sample passes through the column certain components in the sample will be attracted to the packed beads. Those components will take longer to get through the column because they keep getting stuck to the beads as they go through the column. This means that some components in the mixture will fly through the column, while others will take much longer to get through the column because those components keep sticking to the beads and then unsticking. This process is how the HPLC separates the mixture into the different parts. The sample can be separated using size, polarity, or several other chemical properties.
A detector is attached at the end of the column to identify what is coming off the column when. The detector can use many different types of detection, from ultra violet/visible light to mass spectroscopy, to figure out what component of the mixture is coming off of the column at what time.
Overall, the HPLC helps scientist separate and identify, and sometimes even quantify, parts of a liquid mixture.
1) Heit et al. Urine drug testing in pain medicine. Journal of Pain and Symptom Management March 2004. Pages 260–267
For a more thorough walk through and some awesome diagrams of HPLC see:
Harris, Daniel C.. Exploring Chemical Analysis. 4th ed. New York: W. H. Freeman and Company, 2009. Print.
Erin Gallagher is a second year PhD student in Peter Searson’s Materials Science and Engineering lab.