The sampling method developed comprised 30 minutes of sample thermal equilibration at 50°C, followed by a 15-minute analysis over a mass range of 30 to 300 Da. The first three minutes of the analysis served as a blank, during which nitrogen flowed directly from the nitrogen source to the APCI inlet (see 'Blank Route,' Figure ). At the three-minute mark, the six-way valve changed position to immediately swap to the 'Sample Route.' This included an acetone-d6 permeation source (see vial 1 in Figure ) to be used as internal standard, and the whisky sample (see vial 2 in Figure ). After 11 minutes of whisky sampling, at the 14-minute mark, the six-way valve changed position again to the blank route to clear out any volatiles, and to be in the correct position for the subsequent run. source as an internal standard (vial 1), and the whisky sample (vial 2). Both the sample and the permeation source are thermally equilibrated prior to analysis. The permeation source consists of a sealed vial of acetone-d6, pierced with a capillary such that a small but constant quantity of the internal standard is released into the gas stream.