Caffeine Project

Project Overview

For this project I worked with Brad and a fellow student, Will Fox, to determine the caffeine levels in different samples of coffee. For this project we had to make caffeine standards to compare the samples to. The following link describes how we made these standards.

Caffeine Standards

Figure 1. Chemical structure of caffeine

Making the Samples

To make the coffee for the samples, 2.6 oz of beans were weighed out. These beans were then grinded, and 38 g of the beans were placed into a pourover filter. Then, 640 g of boiling hot water were poured over the grounds, allowing the grounds to bloom as needed. This process was done with both L0 and L5 beans.

After this first round of coffee, we discovered that the coffee samples were too concentrated for our standards, so we cut the amount of beans to 30 g of L0 and L5. This round we also made a sample of 15 g of the green coffee beans with 320 g of boiling water. We used a 0.45 micron filter and syringe to put this solution into the HPLC vials to ensure there was no particulate matter present.

After looking at the data from the second round of coffee, we discovered that the concentrations of caffeine in our samples were still too high for our standards. We tested L0 and L5 again, diluting 50% (400 microliters of the sample and 400 microliters of RO water). We also tested L0 samples through the traditional coffee maker, running the grounds through three separate times to analyze how the concentrations of caffeine were affected by extraction. This test was also done with green coffee beans as well.

Once the data for this trial was analyzed, we decided to run L0 samples three times through the coffee maker again to validate our previous results. In this trial, we also tested standards for 300 ppm trigonelline and 10 ppm nicotinic acid, which are both also found in coffee. The trigonelline standard was made by mixing 0.03 g of trigonelline and 100 mL of water. The nicotinic acid sample was made by mixing 0.001 g of nicotinic acid and 100 mL of water.

After all of these trials, we decided to test the amount of caffeine in decaf coffee. 2.6 oz of decaf coffee beans were weighed out and grinded. We then ran these grounds through the coffee maker three times.

Instrumentation

After making the standards, we tested the standards using the HPLC to see where the peaks were for the different concentrations of caffeine. The following link goes into more depth about working with the HPLC.

HPLC

Once the standards were tested, another HPLC trial was done including the L0 and L5 coffee samples.

An additional HPLC trial was done with coffee that was not as concentrated. This set included L0, L5, and the green coffee bean samples.

Data Analysis

To analyze the HPLC data, the data was exported as an arw file. This file was then loaded into Igor, and further analyzed from there. This allowed us to make chromatograms to gain a better understanding of the how each concentration of caffeine absorbs at 273 nm.

References

Monmouth Coffee Project

Journal of Chemical Education Article about the Chemistry of Coffee