Digital Image Colorimetry Smartphone Determination of Acetaminophen

Acetaminophen can be determined colorimetrically via its reduction of ferricyanide to give ferrocyanide. The ferrocyanide formed can then be converted to the highly colored compound, Prussian Blue, via the addition of iron(III). Quantification is commonly obtained by measurement of the absorbance of Prussian Blue at 700 nm using a commercial spectrophotometry instrument. In this present investigation we show the possibility of using the camera of a smartphone to record the blue color developed and, via subsequent use of a downloadable free App, undertake the analysis of the red, green, and blue (RGB) color components to quantitatively determine the concentration of acetaminophen present. A number of free Apps can be downloaded and used to measure the RGB balance of the color of the solution formed. Based on these values a calibration curve to determine the concentration of acetaminophen present can be constructed. This can be undertaken in a number of ways, as demonstrated here, from the red value, expressed as a percentage of the total RGB recorded (%R). From this simple mathematical normalization, it was found possible to obtain a linear relationship with (R2 = 0.994) over the concentration range 5–40 μM of acetaminophen. An associated limit of detection (LOD) of 3.3 μM was recorded. This was found to compare well with that obtained by UV–vis absorbance spectroscopy at 700 nm (R2 = 0.996; LOD 2.7 μM).