Use Your Smartphone as an "Absorption Spectrophotometer"

Smartphone spectrophotometer

A smartphone can be used in a remarkably simple and inexpensive way to teach your students about absorption spectroscopy and Beer’s Law. In short, light reflected off of colored construction paper is passed through a sample and detected by an RGB application on a smartphone. The materials and setup are so simple that students can easily construct several “spectrophotometers” that can be used in a variety of experiments in your classroom. When using the system students learn some basic ideas about the processes involved in a working absorption spectrometer. Excellent results can be achieved; my students routinely obtain absorbance vs. concentration data sets with linear fits of R2 = 0.98 or better.

The video below describes how to set up an iPhone for use as a “spectrophotometer”. Below the video you can find further helpful tips (not covered in the video) on how to set up your own “smartphone spectrophotometer”. For example, the further tips describe how to use an Android instead of an iPhone in the experiment.

Let me know if you use this experiment in your classes. I’d love to hear about any experiments you conduct in your classroom using this set up.

Further tips:

1. This blog post and the video above describe some aspects of the following publication in the Journal of Chemical Education: http://pubs.acs.org/doi/abs/10.1021/acs.jchemed.5b00844. Several other details, as well as a student worksheet, can be found by accessing the publication link.

2. Any application that can detect average R, G, and B values in real time will work. As stated in the video, the application “Colorometer” works well on the iPhone. Further information regarding this app can be found at the following link:  https://itunes.apple.com/us/app/colorometer/id509865412?mt=8.

Two applications that work well on an Android are:

a. “Colorimeter”, (comes with a nominal cost). See: https://play.google.com/store/apps/details?id=com.colorimeter

b. “Colormeter Free”. See: https://play.google.com/store/apps/details?id=com.vistechprojects.colormeterfree&hl=en

3. Because the light detector is an RGB analyzer, it is pedagogically most straightforward to limit the color of background construction paper to be red, green or blue. A color wheel (see below) can be used to help determine the background color of construction paper to be used. To do so, choose the color on the color wheel that is opposite the color of the solution to be analyzed. This “opposite color” is called the “complimentary color”. Since red is the compliment of green, if a green colored solution is to be analyzed, then red construction paper should be used as the background. It may be that the appropriate complimentary color is not red, green or blue. In this case, simply choose a color that closely matches the complementary color. For example, even though orange is the compliment of blue, we have successfully used a red background to analyze blue samples, because red closely matches orange.

4.  As an alternative to colored construction paper, light from a computer screen can be used as a light source. To do so, access the following link on the computer:

http://academo.org/demos/wavelength-to-colour-relationship/ .

a. For blue light, set the wavelength to 440 nm.

b. For green light, set the wavelength to 510 nm.

c. For red light, set the wavelength to 680 nm.

5. It is useful to use drinks that can be bought at the grocery store for stock solutions from which the standard solutions can be made. As seen in the video, we have used Fruit Punch PowerAde Zero as a stock solution of 95±5 x 10-6 M Red Dye #40. We have also used Blueberry Pommegranate Gatorade as a stock solution of 12±1 x 10-6 M Blue Dye #1. Using these solutions as “stock”, we often find the concentration of Blue Dye #1 in Mountain Berry Blast PowerAde to be 4.3±0.5 x 10-6 M and Red Dye #40 in Strawberry PowerAde Zero to be 4.5±0.5 x 10-6 M. 

Join the conversation.

Comments 14

Lowell Thomson's picture
Lowell Thomson | Thu, 03/31/2016 - 16:30

Hi Tom,

Thanks for sharing this. I've been wanting to try this idea for quite some time, and will finally give it a go in May when I have a few extra hours of time once my IB seniors are done. I'll give you an update at that time.

 

Tom Kuntzleman's picture
Tom Kuntzleman | Fri, 04/01/2016 - 20:04

I look forward to hearing about how it goes. Please be sure to send along any suggestions for improvement. Also let me know anything new you learn!

Tom

John Bennett | Fri, 04/01/2016 - 12:11

Hi Tom,

I just got the app on my phone, and I am going to have my senior students not taking the AP exam figure this out once we finish our last unit.  I'll let you know how it goes.

Tom Kuntzleman's picture
Tom Kuntzleman | Mon, 04/04/2016 - 19:29

John:

Good to hear from you! I hope all is well. Let me know how it works out for your students. Let me know if you guys run into any snags or if you have any questions.

Tom

John Bennett | Tue, 04/05/2016 - 08:20

Tom,

All is well.  Tell your family I said hello.

Question: Did you use pure, powdered dyes to determine the concentrations of the fruit punch and blueberry stock solutions used as the standards? Or another method?

Tom Kuntzleman's picture
Tom Kuntzleman | Wed, 04/06/2016 - 15:20

I did not use pure powdered dyes. I used the known molar absorptivity of Red Dye #40 and Blue Dye #1 found in the reference listed here. I then used our Hitachi U-2900 absorption spectrometer to measure the absorbance of the Fruit Punch PowerAde Zero and Blueberry Pommegranate Gatorade. The concentrations of Red Dye #40 in the PowerAde and Blue Dye #1 found in the Gatorade were then found using A = ebc (A is absorbance, e is molar absorptitivity, b is pathlength of cuvette, c is concentration). The results for the concentrations I found using this method were similar - to within the error I cited in the blog -  to what was found at the reference found here. If you do some experimenting and find that my cited concentrations are off, please do let me know so that I can list better values.

Pascual Lahuerta's picture
Pascual Lahuerta | Sun, 04/03/2016 - 11:01

It a great experiment. Students will love it.

Thanks

Pascual Lahuerta

Valencia-Spain

Tom Kuntzleman's picture
Tom Kuntzleman | Mon, 04/04/2016 - 19:30

Thank you so much for commenting, Pascual! Let me know what your students think.

Cheers, 

Tom

John Muench | Mon, 04/04/2016 - 16:39

Tom - I plan to use this next fall for my online chemistry students in some way, shape, or form.  I can't wait to try this myself very soon.  Have you tried manipulating the ambient light in the room at all?  That is, a darkened room with a single lamp on the colored paper?  Thanks for sharing all of your work and any plans to show this at the BCCE this summer?

Tom Kuntzleman's picture
Tom Kuntzleman | Mon, 04/04/2016 - 19:38

Hi John:

Thank you so much for commenting! 

When I was first working out this experiment, I attempted to block ambient light from the sample much as one would do with a real spectrophotometer. When doing this, I was using light from a computer screen as the light source. To use a computer screen as a light source, you can use the following link. I found it worked best if I just allowed the ambient light to fall on the sample and sample box as indicated in the video. I next tried using colored construction paper and found it to work without blocking out ambient light. So no, I haven't tried the set up you describe. I would LOVE for you to try this and report back! Let me know if you get this experiment to work in the manner you describe. In my experience, you don't want too much light, nor do you want too little ambient light. Maybe you can improve upon this experiment. Wouldn't it be cool if we could figure out a way to measure the spectrum- of sorts - of a sample using this simple method?

I think Deanna Cullen will be presenting on this at BCCE this summer, at least that's the plan for now. I've got something else in the works...

Pascual Lahuerta's picture
Pascual Lahuerta | Thu, 04/07/2016 - 02:29

Tom, I regret that I am not teaching anymore. I retired last year. However I follow interesting projects as yours. I passed the information to some teachers so they can benefit from it.

Regards

Pascual

ALFREDO TIFI's picture
ALFREDO TIFI | Fri, 04/08/2016 - 11:41

Hi Tom,

your idea is a very smart and live way to introduce concepts as transmittance and absorbance, and relationships with concentration.

I have found soon an app for Android: ColorMeter Free color picker that is similar to I-phone's.

Did you try to check stability of G% by changing diffuse lighting?

Alfredo

 

Tom Kuntzleman's picture
Tom Kuntzleman | Sun, 04/10/2016 - 15:42

Thank you for your comments, Alfredo. This is a neat way to introduce transmittance, absorbance, Beer's Law, etc. Thank you for the information on the app for Android! We have not checked into how the lighting affects results. Basically, we find you don't want too much nor too little ambient light in the room.