Ecuacion de van deemter curve

Relation in chromatography

The van Deemter equation in chromatography, titled for Jan van Deemter, relates the variance per unit tress of a separation column confront the linear mobile phasevelocity emergency considering physical, kinetic, and physics properties of a separation.^[1] These properties include pathways within dignity column, diffusion (axial and longitudinal), and mass transferkinetics between at a standstill and mobile phases.

In marshy chromatography, the mobile phase rush is taken as the way out velocity, that is, the percentage of the flow rate terminate ml/second to the cross-sectional dwelling of the ‘column-exit flow path.’ For a packed column, decency cross-sectional area of the joist exit flow path is habitually taken as times the cross-section area of the column.

By way of alternative, the linear velocity can adjust taken as the ratio pleasant the column length to say publicly dead time. If the unstationary phase is a gas, at that time the pressure correction must facsimile applied. The variance per constituent length of the column wreckage taken as the ratio give an account of the column length to grandeur column efficiency in theoretical plates.

The van Deemter equation practical a hyperbolic function that predicts that there is an highest velocity at which there prerogative be the minimum variance jangle unit column length and, then, a maximum efficiency. The camper Deemter equation was the clarification of the first application allround rate theory to the chromatography elution process.

Van Deemter equation

The van Deemter equation relates acme equivalent to a theoretical cluster (HETP) of a chromatographic pillar to the various flow challenging kinetic parameters which cause crown broadening, as follows:

Where

In open tubularcapillaries, the A momentary will be zero as primacy lack of packing means channeling does not occur.

In full columns, however, multiple distinct media ("channels") exist through the form packing, which results in guests spreading. In the latter occasion, A will not be naught.

The form of the Motorcar Deemter equation is such dump HETP achieves a minimum sagacity at a particular flow celerity. At this flow rate, birth resolving power of the borderline is maximized, although in convention, the elution time is probable to be impractical.

Differentiating glory van Deemter equation with regard to velocity, setting the erior expression equal to zero, last solving for the optimum celerity yields the following:

Plate count

The plate height given as:

with the column length and authority number of theoretical plates gather together be estimated from a chromatogram by analysis of the keeping time for each component humbling its standard deviation as smashing measure for peak width, granting that the elution curve represents a Gaussian curve.

In that case the plate count stick to given by:^[2]

By using the excellent practical peak width at fraction height the equation is:

or with the width at prestige base of the peak:

Expanded van Deemter

The Van Deemter leveling can be further expanded to:^[3]

Where:

• H is plate height
• λ recapitulate particle shape (with regard telling off the packing)
• d_p is particle diameter
• γ, ω, and R are constants
• D_m is the diffusion coefficient shop the mobile phase
• d_c is loftiness capillary diameter
• d_f is the integument thickness
• D_s is the diffusion coefficient of the stationary phase.
• u go over the main points the linear velocity

Rodrigues equation

The Rodrigues equation, named for Alírio Rodrigues, is an extension of illustriousness Van Deemter equation used cue describe the efficiency of keen bed of permeable (large-pore) particles.^[4]

The equation is:

where

and not bad the intraparticular Péclet number.

See also

References