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Separations

Separations. Column chromatography. Multiple extraction event q n = (V 1 /((V 1 +KV 2 ) n K = partition coefficient = [S 2 ]/[S 1 ] Column Chromatography K = [S] s /[S] m n is analogous to N – the number of theoretical plates

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Separations

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  1. Separations

  2. 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)

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

  4. 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

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

  6. 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)

  7. 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

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