Where 𝑡a is the measured arrival time, t0 is the time spent outside the drift tube and is deduced from the intercept, 𝐿 length of the mobility cell (L = 78.1 cm), 𝜇 is the reduced mass of the analyte/gas couple, 𝑘B the Boltzmann constant, 𝑇 the temperature (T = 296.5 ± 1 K), p the pressure in the drift tube (p = 3.89 ± 0.01 Torr), 𝑁0 = 2.687 x 10 25 𝑚 -3 , p0 = 760 𝑇𝑜𝑟𝑟 and 𝑇0 = 273.15 𝐾.