Effective collision cross section mixtures

Numerous ambient direct ionization methods have been introduced for use with mass spectrometry over the last several years.< - °) A major advantage of these methods is speed of analysis, which is achieved not only by the fast insertion and ionization of the sample, but by the elimination of most sample preparation and chromatographic separations. However, this presents a problem in materials analysis and for mixtures in general because of the complexity of the mass spectra that result from direct analysis of complex mixtures. The atmospheric solids analysis probe (ASAP)< > mass spectrometry (MS) method offers some separation related to volatility by control of the heated gas used to effect vaporization, but this is not sufficient for many mixtures. Ion mobility spectrometry (IMS) offers rapid gas-phase separation of ions based on differences in charge state and collision cross section (CCS) (size/shape). Here we explore the utility of a commercial IMS/MS instrument with ASAP sample introduction for analysis of complex mixtures. 

The effective cross section 6(p0j/ 9) exactly the same as the cross section (pOst) introduced in Section 4.2 for a pure gas. All of the other cross sections introduced depend upon the binary interaction of two molecular species alone, as is made clear by the definition of the Wang Chang-Uhlenbeck or Boltzmann collision operators. From the point of view of the present volume this is a very important result because it means that if the collision cross sections can be determined for each binary interaction, then it becomes possible to evaluate the contribution of that interaction to the transport properties of a multicomponent mixture immediately. If repeated for all possible binary interactions in the mixture then the prediction of the transport properties of any multicomponent mixture containing them is possible. Furthermore, if the effective cross sections for the pure components of a binary mixture are known then those characteristic of the single, unlike binary interaction may be deduced from the properties of a mixture. It is worthy of note that this result remains valid even if higher orders of kinetic theory approximation are invoked. 

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