title: Optimal mixing rate in linear solvent strength gradient liquid chromatography. Balanced mixing program.
abstract: The mixing rate (Rϕ) is the temporal rate of increase in the solvent strength in gradient LC. The optimal Rϕ(Rϕ,Opt) is the one at which a required peak capacity of gradient LC analysis is obtained in the shortest time. The balanced mixing program is a one where, for better separation of early eluting solutes, the mixing ramp is preceded by a balanced isocratic hold of the duration depending on Rϕ. The improvement in the separation of the earlier eluites due to the balanced programming has been evaluated. The value of Rϕ,Optdepends on the solvent composition range covered by the mixing ramp and on the column pressure conditions. The Rϕ,Optfor a column operating at maximum instrumental pressure is different from Rϕ,Optfor a column operating below the instrumental pressure limit. On the other hand, it has been shown that the difference in the Rϕ,Optvalues under different conditions is not very large so that a single default Rϕpreviously recommended for gradient analyses without the isocratic hold also yields a good approximation to the shortest analysis time for all conditions in the balanced analyses. With or without the initial balance isocratic hold, the recommended default Rϕis about 5%/t0(5% increase in the solvent strength per each t0-long increment in time) for small-molecule samples, and about an order of magnitude slower (0.5%/t0) for protein samples. A discussion illustrating the use of the optimization criteria employed here for the techniques other than LSS gradient LC is included.
authors.affiliation: Advachrom, P.O. Box 1243, Wilmington, DE, 19801, USA. Electronic address: leon@advachrom.com.
authors.forename: Leonid M
authors.initials: LM
authors.lastname: Blumberg
authors.affiliation: Department of Chemical Engineering, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Gert
authors.initials: G
authors.lastname: Desmet
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods*; D011312:Pressure; D012997:Solvents
chemical_list: D012997:Solvents
keywords: Balanced isocratic hold; Balanced mixing program; Dimensionless mixing rate; Mixing rate; Optimal mixing rate; Peak capacity; Separation capacity; Speed of analysis