From: nestgrp@earthlink.net
Message-Id: <2.2.32.19970107170324.006a2124@earthlink.net>
Date: Tue, 07 Jan 1997 12:03:24 -0500
Subject: Re: Resolution in Chromatography
To: Recipients of ABRF List <abrf@aecom.yu.edu>
At 02:48 PM 1/7/97 +0100, you wrote:
>I have a theoretical question for all the chromatography specialists among
>the list members.
>During the preparation of a lecture on chromatography I have found two
>different expressions for the calculation of the resolution:
>
>1. R = 0.25 (alpha-1) (square root of N) (k/k+1)
>
>2. R = 0.25 (alpha-1/alpha) (square root of N) (k/k+1)
>
>In both cases the definition of alpha is the same (k2/k1). Can anybody
>explain me if and how these two equations are correlated to each other?
>Which is the "right" one?
>
Peter:
Equation number 2 is the correct equation. Number 1 is either an error or
an over-simplification which does one little good. alpha-1/alpha determines
the selectivity of a separation and is a ratio of the partition coefficients
for any two compounds. Using alpha-1 would not cause too many problems if
you have a low alpha (ie 1.1) since one would get 0.1 and 0.09 respectively.
However, since an alpha of 1.0 is co-elution, one should strive for an alpha
between 1.2 and 1.4 to get baseline separation (trying for an alpha greater
than 1.4 usually gives you diminishing returns). The difference in the
equations is magnified (0.4 and 0.29) for an alpha of 1.4.
Best regards,
John (one of those lurkers)
***********************************
John K. Troyer, Ph.D.
The Nest Group, Inc.
URL: http://world.std.com/~nestgrp
e-mail: nestgrp@earthlink.net
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