Colorimeter out of Mobile

Colorimeter out of Mobile
  1. Take a printout on a paper of the particular color that you solution is going to absorb.
  2. Place that printout behind the solution.
  3. Make a stand as shown in the above video.
  4. Take the RGB reading for the medium with zero concentration of absorbing compound.
  5. Now take the RGB readings for at least three different molarities of the absorbing compound.
  6. The I values will be the sum of RGB values that change. Ignore minute fluctuations
  7. After that use the formula
    A=-log(I/I (with zero concentration))
    to get absorbance values.
  8. Plot the graph of Absorbance vs Concentration and find the best fit line.
  9. Get the equation for the line.
  10. Find the unknown concentration using the slope-intercept equation of that particular line.

If you are having problem taking RGB readings then refer to @jaikishan


At what time you all will come to CUBE lab. I can come if we can rap a demonstration before 3:00

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I recommend that the malaria detector be created as a maker project.

Please echo with Likes. If I get 3 or more, I’ll write it up.


Yeah sure …I’ll be there by 2.

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What’s this malaria detector? Please elaborate @vvcstemplay

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I was hoping if it can be earlier than that because my practical will start by 3 and if we factor in half an hour travel time considering that the buses arrive on time which they don’t we only will have half an hour in our hands.


What is phenolphthalein conjugated hydrogel formation?

It is explained in the paper quoted in the link. Even the molecule is shown.

I don’t have any idea about the pricing and availability of chemicals in India (or anywhere, for that matter). Since the MIT team may have worked with something they could easily access, it is possible that it is not the best for India. Further work is needed. But, for our purposes in STEMgames, the first step is to spell out how to build the detector, and how to test it with the help of a local hospital. The idea can then be pushed through either the state or with the help of NGOs into the field. So, whoever is reading this, please scroll up till you find my request for likes, and I’ll get down to writing it out as a Project

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@pratittodkar Can you try to prove that the application of colorimeter, really works and gives clear reliable results? you can start with different grades of a particular color, and see whether we can determine the absorbance as highlighted in the video you shared?

How are we sure that RGB value is actually the value related to light intensity transmitted from the sample?

Can we prove the device in our mobiles really works?

This would also be essential for building up malaria detector as proposed by @vvcstemplay

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I did a check for the app it didn’t give accurate colors sometimes the difference in measurement was as big as 17% which is very inaccurate. Though the app can serve our purpose since we can still get relative intensity pretty accurate if we keep white balance and exposure of the camera fix.

Hence its not good for getting accurate wavelengths and colors but we could get accurate absorbance and concentrations values.

What do you’ll think about it? Should we go forward with it?

@jaikishan @Sjuday2527


please give evidence… send some pictures of readings obtained in different shades of same color?

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Here is the RGB predicted and original color values.

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Plan of work:

I am going to check whether the app might work for calculating relative absorbance properly and concentration of solution properly.

I am taking a green soap solution and dilute it with water at various concentrations to find out the absorbance values and plot them and then I will try to predict the known concentration using the graph and see whether it matches.

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Did you measure the absorbance of green coloured soap solution?
How, what is the method?
How did you use mobile colorimeter app to measure it?
What were the readings?
How are we sure the readings are correct, how do we calibrate the app?

Ya I did.

For getting a known concentration of solution I mixed the following number of drops of water and soap in the following ratios respectively.

  • 100: 0 ( 0 concentration )
  • 99: 1 ( 0.01 concentration )
  • 95: 5 ( 0.05 concentration )

After which I took the readings for R using the colour picker app from play store Not the colorimetry app since change in exposure and white balance caused error.
Then I measured the absorbance using log calculation done using the formula below.

After that I plotted absorbance in the X axis and the concentration in the Y axis. Then I took got the equation in slope intercept form and predicted the concentration of a known solution and matched with the known value to check it’s accuracy.

Since the soap was in green colour I made the use of red chair as a source of light with the complimentary colour. Then I measured the values of Red in RGB since it was the only colour whose absorbance we were concerned with. Then I did the log calculation for every R value of it’s respective solution.

The readings weren’t accurate but they were close by. And due to making of concentration using drops I think there might have been a error of a drop or so which might have caused the inaccurate readings. The predicted concentration for 0.01 concentration was 0.028. if this is not due to my error then this accuracy could be increased by taking more number of known concentration absorbance values to plot and then finding the best fit line. I used only two values for the graph. The absorbance of 0.00 and 0.05 concentrations.

There is no require for any kind of calibration unless you are interested in the colour as well as concentration.

What is the source of sample colour?
If it is a monitor, have you calibrated the monitor first?


IS the display calibrated?

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@jtd The thing is here there isn’t a need for calibration.

Take this as an example: Suppose if your eyes are seeing a green instead of red and you have learnt to call it red your whole life. It doesn’t matter what colour you are seeing I can still communicate with you and talk to you about the red I see even if your’s is different without we even noticing that we both are seeing different colours.

Something similar is happening here, instead of a need for specific colour we are only discussing relative colour. We are only looking for change in absorbance of the colour we don’t care whether the shade of colour in the camera and reality match. We just want it to be different for each sample in the manner it would theoretically be if it were the actual colour.

I think this is also of relevance in putting this kind of mechanism to use in performing a fast and cheap test for malaria. The colour itself is not as relevant as the absorbance.

Since the original video showed a spreadsheet being used for the actual calculation, can we create a flow chart that can be used to program a yes/no result for the test? This can be disseminated as an app, together with instructions on how to prepare the test blood sample. The main purpose for this test is to enable people in malaria prone areas to start falciparum medication quickly, not to wait for the lengthy standard blood tests results, which takes 5 days.