Analysis of Food Extracts with Thin Layer Chromatography: A STEM Outreach Activity

Abstract

An outreach activity was developed and performed where familiar food items (e.g., beverages, leaves, vegetables, and citrus peels) were extracted with ethanol or ethyl acetate, and the extracts were analyzed through thin-layer chromatography (TLC). The purpose of this activity was to teach participants how chemistry can be used in the real world. Sixteen participants, who were in eighth-12th grade, were divided into four groups with two pairs of individuals. Each group was led by a university student researcher from the advisor's laboratory or by the advisor. The food extracts were analyzed by TLC using solvent systems composed of ethyl acetate and cyclohexane on glass-backed TLC plates with silica gel. After the TLC plates were developed in the solvent chamber, the separated components were visualized using a stain. The pairs of participants repeated the TLC experiment for a second time by choosing their own extracts from different groups to analyze. This outreach activity was deployed at Girls Inc. of San Antonio to show STEM participants how chemistry techniques (extraction and TLC analysis) can be used to separate different compounds from natural sources.

Keywords: Extraction; Outreach Activity; Scientific Method; Thin-Layer Chromatography (TLC).

Figure 1.

Worksheet provided to the participants to fill out during the activity. Two were provided for each participant to allow for performing the experiment a second time.

Figure 2.

Photographs of the different extracts and TLC results (solutions, developed TLC before stain, TLC plate after staining): (A) Group 1 (coffee, green tea, and black tea). (B) Group 2 (spinach, Texas mountain laurel tree leaves, and blueberries). (C) Group 3 (red cabbage, carrots, and tomatoes). (D) Group 4 (lemon, lime, and orange). Groups 1–3 items had 300 mg of material weighed out. Group 4 items had 500 mg of material (peels of citrus fruits). Carrots, tomatoes, spinach leaves, leaves from outside, and blueberries were dissolved in 1 mL of ethanol and 1 mL of ethyl acetate/cyclohexane (v/v). The other items (i.e., coffee, green tea, black tea, red cabbage, lemon peel, lime peel, and orange peel) were dissolved in 1 mL of ethanol. The spots were developed in a solvent system comprising 1:1 ethyl acetate/cyclohexane (v/v).

Figure 3.

(A) TLC plate of the “mix-and-match” experiment (second round of TLC analysis of comparing solutions from different groups) participants performed after the first TLC experiments before staining the plate to visualize the compounds. From left to right: orange, spinach, carrot, coffee, and co-spot. (B) TLC plate from part A after staining with the ceric ammonium molybdate stain. (C) Back of the stained plate from part B.

Figure 4.

(A) Prelab and (B) postlab assessments were handed out in the beginning and end of the activity.