Here, students determine aspirin (acetylsalicylic acid) mass in pharmaceutical tablets using a colorimetric method. Aspirin, salicylate, and salicylic acid do not absorb visible light. Thus, in alkaline medium, acetylsalicylic acid was hydrolyzed to salicylate; then, it was reacted with an acidic Fe(III) solution, and a violet complex was formed. Quantitative analysis was carried out using absorbance measured at 535 nm (standard method) and digital images obtained with a flatbed scanner (proposed method). Results obtained with both methods were compared using an F-test and a t-test; both methods had shown equivalent accuracy and precision at the 95% confidence level. In addition, one-way ANOVA showed that aspirin masses found by five student groups using both methods are equivalent at the 95% confidence level. In the proposed method, samples were placed in a 96 microwell plate, and RGB values were extracted automatically from all wells in less than 5 min using ImageJ's plugin "ReadPlate"; data obtained were organized using a spreadsheet to determine aspirin mass in pharmaceutical tablets, recovery, and percent error. Our goal was to design a portable, cost-effective, and user-friendly platform and to develop an experimental methodology that can easily be applied to any research and education laboratory using just a flatbed scanner.

In this research, it was presented a laboratory class where titrimetric and colorimetric methods were used to determine vitamin C levels in supplement pills. In the first part, vitamin C levels were measured in supplement pills using three titrimetric methods, back titration with sodium thiosulphate (Na2S2O3), direct titrations with potassium iodate (KIO3) and iodide (I2). Results obtained with trimetric methods were equivalent at 95 % confidence interval, methods were compared using one-way ANOVA). In the second part, a quick and low-cost colorimetric method was carried out. It was successfully used to measure vitamin C levels in supplement pills. It consists in reduction of the complex Fe 3+ and 1,10phenanthroline by vitamin C to form a reddish-orange colored complex that was measured at 510 nm. The colorimetric method was also carried out using digital images obtained with a flatbed scanner. RGB values were extracted from digital images using ImageJ's plugin ReadPlate in a simple and easy manner. The t paired test had shown that both methods were equivalent at 95 % confidence interval.