Simultaneous Determination of Ni(II) and Co(II) in Aqueous Solution Using an Image-Based Do-It-Yourself Photometer

The principle of additivity of absorbances is a crucial method that can be used in the determination of two components individually from a mixture using a colorimeter/spectrophotometer. In this laboratory experiment, postgraduate students were introduced to the principle of additivity of absorbances and its application in the determination of nickel (Ni­(II)) and cobalt (Co­(II)) from unknown samples. The experiment provided students with a hands-on experience in the construction of a do-it-yourself (DIY) photometer containing three different light-emitting diode (LED) filters using low-cost, easily available materials. The students prepared the working standards of Ni­(II) and Co­(II) and captured their images in three different LED lights: red, green, and blue, which worked as filters. The images captured were then analyzed using ImageJ software, and RGB values from the images were extracted and converted to absorbances. The absorbances obtained from the images of different solutions of Ni­(II) and Co­(II) were plotted against their respective concentrations. Ni­(II) showed a good regression coefficient value for red component absorbance that was recorded in the red LED filter, and Co­(II) showed a good regression coefficient value for green component absorbance that was recorded in the green LED filter. The individual calibration curves of Ni­(II) and Co­(II) constructed in the presence of red and green LED filters were further used to determine individual concentrations of Ni­(II) and Co­(II). The calibration curves were constructed in Microsoft Excel, enhancing students’ data entry skills. This experiment provides an easy method for the construction of a DIY photometer based on a smartphone as a detector with LED light filters, making it useful for teaching the simultaneous analysis of analytes from a mixture by using the principle of additivity of absorbances.