Determination of Cr (VI) released by leather samples using smartphone-based colorimetry for on-site determination and miniaturization as greener preparation strategy

• A miniaturized method for detecting Cr (VI) released by leather samples. • Smartphone-based analyses achieve LOD = 0.0202 µg mL -1 and LOQ = 0.0612 µg mL -1 . • Reduced environmental impacts compared to the reference method. In this work a lab-on-a-smartphone platform for on-site and rapid assessment of Cr (VI) released by leather samples has been proposed. In comparison with the reference method (BS EN ISO 17,075–1:2017) the newly developed one permits to reduce the amount of extractant solution up to 10 mL (100 mL for the reference method) through a miniaturization step. The released Cr (VI) was determined after the reaction with 1,5-diphenylcarbazide using a smartphone equipped with Photometrix®. This approach achieves LOD = 0.0202 µg mL -1 and LOQ = 0.0612 µg mL -1 very closed to the reference method which allows the adoption of this miniaturized method for analysis of real samples. The analyses were carried out on Cr-tanned leather samples with encouraging results favouring the on-site determination which will be further explored as quality control test in the leather industry. The developed method permits to reduce environmental impacts, determined by using both AGREE and AGREEprep, related to Cr (VI) determination in terms of produced waste and energy consumption allowing the process of an higher number of samples as a function of time.