Mobility calculation formulas

Apparent mobility of analyte A, m_app,A is calculated according to equation (1):

L_eff - effective capillary length (from injection end to the detector position)

L_tot - total capillary length

U_sep - applied separation voltage

t_mig,A - migration time of the analyte A (in Gaussian peaks = migration time of peak apex).

 

Effective electrophoretic mobility, m_eff,A, is defined by eq. (2):

m_EOF is mobility of electroosmotic flow (EOF) calculated according to eq. (3):

t_mig,EOF - migration time of the electroneutral compound (marker of EOF)

 

Substitution of equations (1) and (3) into equation (2) gives the following equation for effective electrophoretic mobility of analyte A, m_eff,A:

 

Alternatively, mobility of EOF, m_eof, can be determined from the apparent and effective mobilities of a reference analyte R, m_app,R and m_eff,R, respectively.

m_app,R is calculated according to eq. (1), where t_mig,A is replaced for migration time of reference analyte R, t_mig,R:

 

Substitution of equations (6) into equation (5) gives the following equation for the electroosmotic flow mobility, m_EOF:

 

Effective mobility of reference compound R, m_eff,R, has to be known from the previous measurement in the same background electrolyte and at the same temperature, at which the apparent mobility of analyte A is measured.

Effective electrophoretic mobility, m_eff,A, is then calculated according to eq. (2), where m_app,A is obtained from eq. (1) and the electroosmotic flow mobility, m_EOF from eq. (7).

For the special case, when reference analyte R is electroneutral compound (EOF marker), i.e. m_eff,R = 0 and t_mig,R = t_mig,EOF, the eq. (7) becomes identical to eq. (3) and effective mobility of analyte A can be calculated according to eq. (4).