Acrylamide determination was performed according to the method of. In brief, acrylamide was extracted by 10 mL of water and the extract purified by a single SPE column consisting of 0.5 g of a mixture of C18, strong cation (SCX) and anion exchange (SAX) sorbents in the ratio 2/1.5/1.5 (w/w/w). The quantitation was carried out by liquid chromatography-tandem mass spectrometry using d3-acrylamide as internal standard. The relative response factor of acrylamide with respect to d3-acrylamide was calculated daily as the average of the response factors obtained by analysing a standard solution a minimum of three times.