Development of a 3D-Printed Photometric Device for the Determination of Urea in Milk Samples

This work reports the development and application of a user-friendly, portable, and low-cost 3D-printed photometer for the detection of urea adulteration in milk. The method is based on a colorimetric reaction with p-dimethylaminocinnamaldehyde combined with a rapid (30 min), economical, and environmentally friendly sample preparation involving calcium chloride salting-out and acidification (pH 3.8), forming a chromophore with maximum absorption at 530 nm. The device demonstrated a linear range of 4.0-40 mg mL^-1, a limit of quantification of 4.0 mg mL^-1, recoveries of 97-105%, and intra- and interday precision between 1.43% and 3.39% in whole and skim milk. Results were statistically comparable (p > 0.05) to a benchtop spectrophotometer and HPLC-UV-vis. Released as open-source hardware under CC BY-SA 4.0, this analytical platform combines low-cost fabrication, modular electronics, and wireless capabilities to provide decentralized, accessible, and high-accuracy milk quality monitoring, thereby strengthening food safety while reducing analytical costs and environmental impact.