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Spring SAVY 2017, Day 4- Chromatography 101

Posted by on Monday, February 20, 2017 in Grade 5, Grade 6, SAVY blog.

At the conclusion of last week’s class, I had asked the students to describe some of the challenges of performing column chromatography. Answers included that it took a long time to elute the desired compounds from the column and that holding the tubes for collecting the samples was rather tiresome. The students also mentioned that if the plant pigments had not been colored, it would have been difficult to determine when they were coming off of the column. Thus this week I presented a technique that seeks to address many of these concerns: High-Pressure Liquid Chromatography (HPLC).

HPLC is a chromatographic technique in which mobile phases (often more than one) are pumped (via an automatic pump) over a very thin column (the stationary phase). As one might imagine, this generates quite a bit of pressure (a large amount of liquid being pumped quickly through a small opening), hence the naming of the technique “high-pressure” liquid chromatography. The method of detection in HPLC varies but is often a UV detector. The entire system is associated with a computer to provide a real-time readout of the results as different compounds elute from the column. We visited my lab to see a few different types of these HPLC systems in action.

When we returned, we used our knowledge of HPLC to solve a type of problem encountered by environmental engineers. The students were tasked with determining which polycyclic aromatic hydrocarbons (PAHs) were present in water samples and at what levels. PAHs often end up in urban/suburban water sources through road run-off near industrial manufacturing facilities and can pose a significant human health risk since many have been identified as carcinogens. The retention times of each compound are unique (the amount of time they remain on the column) and there is a linear relationship between the concentration of PAHs and their UV absorbance. I encourage you to ask your student to explain how they developed a standard curve to determine contaminant concentrations and to ask them if the levels of compounds met or exceeded EPA regulatory standards. I also encourage you to read this short article about PAHs in wastewater with your child, if they are interested (https://wrri.ncsu.edu/docs/partnerships/bmc/PAHFactSheet.pdf). This particular lab experiment was more challenging than previous ones, so we will wrap up our discussion of this lab next week.

See you then!

–Michelle

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