Once extracted, the coffees were quickly cooled on ice and diluted
with distilled water until a final volume of 150 mL. 100 mg of cysteine
was added to the coffee samples to avoid thiol binding to the coffee
matrix during sample work up. Definite amounts of isotope labelled
standards were spiked into thewater phase (Table 1) and the solutions
were stirred for 10 min (at room temperature). Subsequently, portions
of 7 mL were transferred to headspace vials