Abstract:

One of the most important contents in the Analytical Chemistry syllabus is the different kind of calibration approaches that can be used. Among others, external calibration, standard addition and internal standard are the most commonly taught ones. Their interpretation is often misunderstood by a significant fraction of the students, who find difficulties in spotting the differences, either in the preparation, application or calculations. This results in the students not being able to prepare each kind of calibrate when needed in the lab.

In this contribution we propose a colour-based teaching procedure that can be easily carried out in class, without the need of sophisticated or extensive materials, or without having to go to the laboratory. To this end, different tubes are handed to the students, along with some coloured solutions using food dyes, a dropper, and water. Each one of these solutions represent an important component of the calibrations: either the sample, the blank, or the standard, and thus must be combined according to the calibration strategy that should be prepared. Additionally, a hand-out is shared with the students describing the protocol to follow for the preparation of each solution. In a qualitative way, students follow the instructions, obtaining three different kinds of calibrations, one per strategy: external, standard addition and internal standard.

Thanks to the visual component of the coloured solutions, the understanding of how to prepare each calibration, which components must be added, and what’s the final result is enhanced. In this way, the instructor is provided with an additional teaching tool which counteracts the fact that teaching a very practical aspect only by means of theoretical content usually falls short. Also, this proposal can be carried out in the lecture hall, either individually or in groups, according to the conditions of each group.

Keywords:

Analytical Chemistry, Color, Calibration.