question on isocratic elution

[rick1112]

hi

well this question came to me when i was reading a post on IEC...
in isocratic elution condition... the sample/analyte are in contionus motion and seperation happen due to the difference in solubilit in mobile phase and stationary phase of different substance in the sample...
having said that does the size/shape of sample/analyte have any influence in elution and seperation...??

(P.S. plz correct me if i got something wrong.. i have work less on isocratic elution method...still a child in the field of chromatography )

[tom jupille]

You have answered your own question. Chromatography is based on equilibrium of the analyte molecules between the stationary phase and the mobile phase. This equilibrium is controlled by relative affinity for the stationary phase and affinity for the mobile phase. Analyte size and shape will affect both, so they will affect chromatographic retention.

[rick1112]

hi

what i would really like to know is that, the effect of shape and size of analyte only has effect in isocratic elution condition or does this also have effect on gradient elution??? (if so, is the effects same in both situation)

thanks

[tom jupille]

Effects are the same in both gradient and isocratic. You can think of gradient elution as a series of isocratic steps.