CONCEPT OF EFFECTIVE-MASS AND HIDDEN MASS FOR CALCULATION OF MOBILITYOF ORGANIC-ANIONS AND PEPTIDES

The concept presented for the calculation of electrophoretic mobility is based on three assumptions: (1) the molecular mass M can be treated as composed of effective mass E and hidden mass H, M = E + H; (2) the mobility u is proportional to the charge Z and inversely proportional to the effective mass to the power 2/3; and (3) both E and H are addi tive functions of composition. Butyric acid was chosen as a standard f ulfilling the condition M = E, H = 0, resulting in the equation u = 66 8ZE(-2/3) . 10(-5) cm(2) a V-1. The suggested approach involves the su mmation of all special contributions to the hidden mass and calculatio n of the mobility from the effective mass E = M - Sigma H. The total h idden mass involves values dependent on hydrocarbon structure, H-alpha , dependent on functional groups, H-beta, and contributions of certain subunits such as amino acids in peptides, H-r. The H-alpha contributi ons for aliphatic compounds can be expressed as a function of the meth ylene (together with CH3 and CH but with the exception of CHOH chains) group content in the molecule. H-alpha for aromatic compounds depends on the nature of the aromatic ring. The special contributions were de rived from the mobilities of about 200 compounds. Mobilities calculate d by the suggested approach indicate an average relative error of +/-1 .5% for organic acids and +/-0.8% for peptides.