Comprehensive estimation of measurement uncertainty in determination of antioxidant activity in natural product by 2,2ʹ-diphenil-1-picrylhydrazyl (DPPH) radical scavenging assay

A comprehensive estimation of measurement uncertainty of antioxidant activity determination using 2,2′-diphenil-1-picrylhydrazyl (DPPH) radical scavenging assay is presented according to the EURACHEM Guide with Mengkudu (Morindra citrifolia L.) extract as model sample. The uncertainty sources contributing to the measurement uncertainty include: (1) experimental precision, (2) preparation of DPPH solution, (3) preparation of extract solution, (4) preparation of final mixture solution, (5) the use of micropipette and (6) volumetric pipette. Employing fishbone diagram to identify the relationship between sources, the combined and expanded uncertainty was determined for a practical example. Mengkudu extract has an average of 59.20 DPPH radical scavenging activity with total combined uncertainty of 1.01. However, considering the estimation of expanded uncertainty, the true value of antioxidant activity lies between 59.20 ± 2.02 for 95 confidence level. This estimation increases confidence in the validity of a measurement result when reporting quantitative analysis result for the purpose of making important decision as well as fulfilling legislative requirements if needed.