Figure 1 : Schematic illustrating key steps involved in colorimetric measurements using a smartphone [1].

Computers are an indispensable part of laboratories. However, arrival of powerful mobile devices in the last few years and ever expanding ecosystem of scientific apps is all set to change that and usher in "there's an app for that" culture in laboratory workflows. 

Chemists have just begun to realize the usefulness of mobile devices in their research work. There are mobile apps for reading journal articles and ebooks, accessing databases and reference material, drawing structures, and much more. Adding to this trend, researcher B.-Y. Chang proposes a method to carry out colorimetric measurements using mobile devices in his paper titled "Smartphone-based Chemistry Instrumentation: Digitization of Colorimetric Measurements" [1].

Colorimetric measurements are routinely done in physical and analytical chemistry laboratories to find the concentration of a coloured chemical in a solution. Colorimeters like spectrophotometers are used to measure light absorbance of the solution, and then Beer-Lambert Law is applied to find concentration of the chemical.

The paper demonstrates the concept of using the camera of a mobile device to find the proton concentration of a solution. Key steps of this method are (Figure 1) :

1. Take a single picture of a pH paper with colours of reference pH and samples' pH.

2. Generate a calibration curve from the reference colours.

3. Find the colour positions of the samples on the calibrated curve.

Since digital cameras have RGB filters [2], it was difficult to distinguish between colours in a picture and determine the correct concentration. To overcome this problem, RGB values were transformed to HSV color space [3] using Matlab and then H values were used, instead of wave length of light, on the Y-axis of the calibration curve to discriminate between all the colours and determine samples' pH (Figure 1).

Once an easy to use mobile app for carrying out colorimetric measurements is ready, smartphone users would have access to a less expensive, less time consuming and a very "handy" alternative to bulky spectrophotometers. Another advantage of this method over traditional colorimetric measurements is that it doesn't require background signal correction as colour types are identified in HSV space and is independent of light intensity of colours. 

Growing number of mobile apps for chemists augur well for "lab-on-a-mobile-device" concept going mainstream. From here on one can expect more innovative use of inbuilt sensors in mobile devices [4] as a substitute for laboratory instruments.

Read the full research article here.


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