the headspace vial is 1 mL.When working in internal standard mode, 120 µL of n-propanol is also added to give a concentration of 0.1 g/dL into the headspace vial. To analyze real samples, transfer 1 mL of a biological specimen into a 20 mL headspace vial, add 120 µL (0.1 g/dL) of the n-propanol internal standard, apply the vial cap, and mix.