Separations

Column chromatography Multiple extraction event qn = (V1/((V1+KV2)n K = partition coefficient = [S2]/[S1] Column Chromatography K = [S]s/[S]m n is analogous to N – the number of theoretical plates N depends on separation efficiency (H) and length of the column (L)

Characterizing the Retention Parameters for a given Application Retention coefficient or capacity factor k’ = (tr-tm)/tm

Selectivity factor Selectivity factor for A and B– a ..a = k’B/k’A = [(tr)B-tm] / [(tr)A-tm] Depends on properties of A and B and experimental conditions Independent of flow rate Good way to evaluate performance of column

Parameters of Column Plate Height – H = s2/L = L/N For Gaussian peak = LW / 4tr H = LW2 / 16t2r N = 16(tr/W)2

Separation of two components Resolution R = [(tr)B – (tr)A] / Wave R = N1/2/4 [(a-1)/a] [k’B/(1+k’B)] Can adjust resolution by changing N, a, and k’B. Adjusting a and k’B Mobile phases, temperature, stationary phases, additives Adjusting N Changing column (length or diameter)

Column Efficiency - H Van Deempter Equation H = A + B/v + Cv There is a optimal linear flow rate for a given column GC is generally more efficient than HPLC due to practicality of longer columns