24_Chromatography-page3

24_Chromatography-page3 - The average linear rate for the...

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Unformatted text preview: The average linear rate for the solute is: v = L / tR where L is the column length. And for the mobile phase it is: u = L /tR VR or tR where VR = tR x flowrate This is simply the time required for a noninteracting substance to pass through the column. v=uxf v =u f is the fraction of time that the solute spends in the mobile phase. =u Since both the mobile and stationary phases have known volumes (VM, VS), we can now determine K - our partition coefficient. 1 This shows the factors required to have a component elute and how two materials can be separated. Each material has its own K. As K increases, elution takes longer. Other terms affect the overall separation. ( =u f = n soluteM / n soluteS v=u( 1+KV /V ) S M CMVM CMVM +CMVS ( 1 1+ CSVS CMVM 1 1+ K VS VM ) ) Raising VS General increase in retention VM General decrease in retention u Increases speed of separation. VS and VM can be altered by changing column diameter and length for a specific column packing. u can be altered by changing the flowrate. All terms can be found by knowing how the column was prepared. ...
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