A method of determining characteristics of predetermined molecules using a processor, the method comprising: the use of a combined ion mobility-mass spectrometry (IM-MS) technique for experimentally determining a range Z of molecular structures; estimating the cross sectional area of molecules comprising the steps of: A) Predicting the geometric structure of the molecule of interest; B) Assigning an ellipsoidal boundary containing the whole of said molecule; C) Randomly selecting an orientation of the assigned ellipsoidal boundary together with its contained molecule; D) Calculating a value for the area contained by the elliptical boundary formed by the projection of the ellipsoid onto a plane at said randomly selected orientation; E) Randomly selecting a position within the elliptical boundary; F) Identifying whether the position within the elliptical boundary also falls within the cross sectional area of an atom within the molecule of interest; G) If said F) criterion is met, setting said cross sectional area of the molecule at said orientation to the cross sectional area contained by the elliptical boundary calculated in D, if said F criteria is not met, setting said cross sectional area of the molecule to 0; H) Calculating an averaged cross sectional area over all said randomly selected orientations; I) Iterating steps C) to H) for at least N iterations and/or until M independent calculations of the averaged cross sectional area agree within a predetermined range R for X iterations; and comparing values of said range Z with those estimated, wherein the method further correlates the differences in the molecular structures with differences in selected predetermined activity of those molecules. the use of a combined ion mobility-mass spectrometry (IM-MS) technique for experimentally determining a range Z of molecular structures; estimating the cross sectional area of molecules comprising the steps of: A) Predicting the geometric structure of the molecule of interest; B) Assigning an ellipsoidal boundary containing the whole of said molecule; C) Randomly selecting an orientation of the assigned ellipsoidal boundary together with its contained molecule; D) Calculating a value for the area contained by the elliptical boundary formed by the projection of the ellipsoid onto a plane at said randomly selected orientation; E) Randomly selecting a position within the elliptical boundary; F) Identifying whether the position within the elliptical boundary also falls within the cross sectional area of an atom within the molecule of interest; G) If said F) criterion is met, setting said cross sectional area of the molecule at said orientation to the cross sectional area contained by the elliptical boundary calculated in D, if said F criteria is not met, setting said cross sectional area of the molecule to 0; H) Calculating an averaged cross sectional area over all said randomly selected orientations; I) Iterating steps C) to H) for at least N iterations and/or until M independent calculations of the averaged cross sectional area agree within a predetermined range R for X iterations; and comparing values of said range Z with those estimated, wherein the method further correlates the differences in the molecular structures with differences in selected predetermined activity of those molecules. A) Predicting the geometric structure of the molecule of interest; B) Assigning an ellipsoidal boundary containing the whole of said molecule; C) Randomly selecting an orientation of the assigned ellipsoidal boundary together with its contained molecule; D) Calculating a value for the area contained by the elliptical boundary formed by the projection of the ellipsoid onto a plane at said randomly selected orientation; E) Randomly selecting a position within the elliptical boundary; F) Identifying whether the position within the elliptical boundary also falls within the cross sectional area of an atom within the molecule of interest; G) If said F) criterion is met, setting said cross sectional area of the molecule at said orientation to the cross sectional area contained by the elliptical boundary calculated in D, if said F criteria is not met, setting said cross sectional area of the molecule to 0; H) Calculating an averaged cross sectional area over all said randomly selected orientations; I) Iterating steps C) to H) for at least N iterations and/or until M independent calculations of the averaged cross sectional area agree within a predetermined range R for X iterations; and