To evaluate the uncertainty for the determination of melamine residue in milk powder by gas chromatography-mass spectrometry (GC-MS).

Following the Guidance on quantifying uncertainty in chemical analysis (CNAS-GL006: 2019), a mathematical model was established to analyze and evaluate the sources of uncertainty in the determination of melamine residue in milk powder by GC-MS according to the Chinese National Standard Determination of melamine in raw milk and dairy products (GB/T 22238-2008). The combined standard uncertainty was calculated from the uncertainty components.

The melamine content of the milk powder sample was determined to be 2.090 mg/kg with an extended uncertainty of 0.182 mg/kg (k = 2).

The uncertainty mainly came from sample volume adjustment, sample recovery, standard solution preparation and curve fitting.