Mass stereoselectivity factor

Besides the conventional factors causing peak broadening in LC. another source for lower efficiency in LC with chiral stationary phases may be the existence of at least two different adsorption sites (the stereoselective and non-stereoselective ones) that may considerably differ in their adsorption kinetics (heterogeneous mass transfer kinetics) and thus cause peak broadening and tailing. These factors have been investigated and modelled by Fomstedt et al.. e.g. for protein type CSPs [75,91-9.3] and their contribution was determined for different analytes and different type of CSPs (bovine serum albumin, cellobiohydrolase 1, tris(4-methylbenzoyl) cellulose) [94j. In a recent study, these authors reported on the adsorption isotherms as well as selective and nonselective contributions of propranolol enantiomers on a cellobiohydrolase 1 CSP in dependence of the mobile phase pH [95[. 

The above example provides some hints as to when mass transfer could be a complicating factor in stereoselective hydrogenations. If the reaction half-time is of the order of minutes, and the product distribution depends on H2 pressure, then mass transfer might affect the observations. In either case, the effects of mixing rate and catalyst concentration (i.e. variation of the overall rate) should be investigated. 

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