▁ ▁Where ▁▁ ▁H ET P ▁= ▁ ▁a ▁measure ▁of ▁the ▁resol ving ▁power ▁of ▁the ▁column ▁[ m ] ▁ ▁A ▁= ▁Edd y - diff usion ▁parameter , ▁related ▁to ▁channel ing ▁through ▁a ▁non - ide al ▁pack ing ▁[ m ] ▁ ▁B ▁= ▁diffusion ▁coefficient ▁of ▁the ▁el uting ▁particles ▁in ▁the ▁longitud inal ▁direction , ▁resulting ▁in ▁disp ersion ▁[ m 2 ▁s − 1 ] ▁ ▁C ▁= ▁Res istance ▁to ▁mass ▁transfer ▁coefficient ▁of ▁the ▁analy te ▁between ▁mobile ▁and ▁station ary ▁phase ▁[ s ] ▁ ▁u ▁= ▁Linear ▁Vel ocity ▁[ m ▁s − 1 ] ▁ ▁In ▁open ▁tub ular ▁cap ill aries , ▁the ▁A ▁term ▁will ▁be ▁zero ▁as ▁the ▁lack ▁of ▁pack ing ▁means ▁channel ing ▁does ▁not ▁occur . ▁In ▁pack ed ▁columns , ▁however , ▁multiple ▁distinct ▁routes ▁(" ch annels ") ▁exist ▁through ▁the ▁column ▁pack ing , ▁which ▁results ▁in ▁band ▁spread ing . ▁In ▁the ▁latter ▁case , ▁A ▁will ▁not ▁be ▁zero . ▁ ▁The ▁form ▁of ▁the ▁Van ▁De em ter ▁equation ▁is ▁such ▁that ▁H ET P ▁ach ieves ▁a ▁minimum ▁value ▁at ▁a ▁particular ▁flow ▁velocity . ▁At ▁this ▁flow ▁rate , ▁the ▁resol ving ▁power ▁of ▁the ▁column ▁is ▁maxim ized , ▁although ▁in ▁practice , ▁the ▁el ution ▁time ▁is ▁likely ▁to ▁be ▁imp ract ical . ▁D iffer enti ating ▁the ▁van ▁De em ter ▁equation ▁with ▁respect ▁to ▁velocity , ▁setting ▁the ▁resulting ▁expression ▁equal