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The science
What is modelled
Three compounds are injected as a narrow plug. In the column each molecule is either carried along by the gas or adsorbed on the stationary phase. The ratio of time spent in the stationary phase to time in the gas is the retention factor k, which falls as the oven gets hotter. The detector counts molecules reaching the outlet.
Equations
Retention time t_R = L(1 + k)/u. Temperature dependence k(T) = k_ref·φ·exp[(ΔH/R)(1/T − 1/T_ref)]. Each molecule is a two-state random walker: mobile with drift u and diffusion D, or stationary; switching probabilities per step are 1 − exp(−4.4·k/(1+k)·Δt) (adsorb) and 1 − exp(−4.4/(1+k)·Δt) (desorb), which gives the equilibrium ratio k.
Honest simplifications
A stochastic transport model with three illustrative compounds and one switching rate, not a full van Deemter or mass-transfer model; the ramp is linear, the column is isothermal along its length, and the detector has no response time. 480 molecules per compound make the peaks noisy on purpose.
Built-in checks
Mass balance of injected and detected molecules, mean retention time of an isothermal test run against L(1 + k)/u, and the van t Hoff slope of ln k against 1/T.