Well, not the type of beer you are thinking of. Have you ever woken up early ready for a fresh cup of coffee only to find that you failed to notice that you ran out?
Living in Florida has taught me to be prepared for many situations…
- Scorching sun? Stock up on sunscreen!
- Intense heat and humidity? Make friends with someone who has a pool!
- Hurricanes? Stock up on essentials that can be made with no electricity!
After standing at my kitchen counter staring at the empty coffee canister I remembered that I did indeed prepare for this day. Time to break out the instant coffee!
Now, we know there are many preparations for coffee (some being better than others). Instant coffee is probably one of the ways to make coffee that is on the ‘not so great (but give me the caffeine)’ side. Using just the instant grounds and hot water you can make coffee essentially anywhere!
We use solutions all the time as part of our everyday life. Different concentrations of a solute can yield different results. It’s important to know the concentration of the mixture that you are using. One way that you can test for concentration is using the Beer-Lambert Law. By measuring the absorbance of a solution you can find out the concentration.
Absorbance is related to the number of photons a sample absorbs. When an atom or molecule absorbs a single photon, an electron makes a transition to a higher orbital energy. As the number of atoms or molecules increases more photons can be absorbed. The number of photons a sample absorbs is directly related to the number of atoms or molecules that are present in the sample.
Absorbance (A) is defined as the ratio of the number of photons before and after the light beam passes through a sample : A=log(P0P) Where P0 = number of photons before and P = the number of photons after. This absorbance is directly proportional to the concentration.
So – how does this mix with coffee? I haven’t used instant coffee in quite awhile, so we are going to find the perfect mixture of water to instant coffee. Now, ideally I’d measure the concentration of caffeine but since I’m working from home I don’t have any of the tools required for this. Plus, we can measure caffeine content by UV absorbance (typically at 260nm). While I do have an SL5-CUV (UV-VIS light source) I only have plastic cuvettes. So, we will be creating the perfect cup of instant coffee based off of color instead of caffeine content.
I’ve prepared a few samples with known concentrations:
| Sample 0 | Sample 1 | Sample 2 | Sample 3 | Sample 4 | Sample 5 | |
| Coffee (g) | 0 | 1 | 1 | 1 | 1 | 1 |
| Water (mL) | 100 | 150 | 120 | 100 | 80 | 60 |
| Calculated Concentration (g/mL) | .00 | .0066 | .0083 | .0100 | .0125 | .0166 |
After preparing the samples, I optimized the conditions by changing the integration time and number of scans to average. Once I was happy with the SCOPE mode spectra I took a dark and light measurement. From here, I switched to absorbance mode and took measurements for each sample, including an unknown that I made by mixing an unknown amount of instant coffee to water.
Here are some spectra!
This is in SCOPE mode of all the measurements overlaid:
Here is absorbance mode with all the spectra overlaid:
So, my perfect mixture to the eye is somewhere between sample 4 and sample 2.
From here what I can do is export the data to excel and create a calibration curve. Or I can use the ChemWiz concentration Predictor to create a method.
You can use this tool to do concentration analysis on a single wavelength. When you are taking your measurements you can press the “Save Sample” key and view the results in the data log. You can create many different methods for different solutions to make your measurements quick and easy.
I chose to make a calibration curve in Excel:
The green data point is our unknown.
Now it’s time to drink all the samples!
Home Quarantine Article by Stephanie Boxel
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