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Generalized NLC Models

The Wade-Thomas NLC Parameters

See the NLC topic for detailed references of the NLC model.

Assuming the time scale has been properly transformed, the a₁ “center” parameter is the true thermodynamic capacity factor k’, the retention time at infinite dilution. With highly tailed peaks, k’ will occur well after the peak maximum. The time transformation can be carried out as follows: X=X/t₀ -1, where t is the dead time of the column.

The a₂ width parameter is exactly analogous the Giddings equation. It has physical significance in that its inverse is actually a dimensionless time constant:

where k_d is the solute desorption constant, and t₀ is the dead time of the column.

The a₃ distortion parameter can be used to derive the equilibrium constant, and thus the adsorption rate constant as well (since k_d is known from a₂). Note that the GenNLC's a₃, in order to share an identical a₃ distortion parameter as that of the GenHVL and HVL models, is twice that of the NLC:

Generalized HVL and Generalized NLC Equivalence

The Generalized NLC models in PeakLab are constructed using the shape equivalence of the GenHVL and GenNLC models with a common assumed density.

This approach allows any Generalized HVL model to be converted into an equivalent Generalized NLC, but specifically assumes the simple first-order Giddings kinetics for the a₂ time constant parameter.

Parameter Description

In general, the following applies:

a₀ = the area or zero moment parameter

a₁ = parameter related to first moment, the center value (this will be model specific)

a₂ = kinetic parameter related to the peak width or the square root of the second moment (this will be model specific)

a₃ = the NLC/HVL chromatographic distortion parameter (fronted for a₃<0, tailed for a₃>0) (identical across all GenNLC and GenHVL models)

a₄ = for 5 parameter models, the parameter relating to the skew or third moment; for 6 parameter models, the parameter relating to the kurtosis or fourth moment

a₅ = for 6 parameter models, the parameter relating to the skew or third moment

The Generalized NLC Models

NLC (Full Range)

GenNLC - Generalized Normal ZDD

Gen2NLC - Generalized Error Model ZDD

GenNLC[Z] - [Z] Generalized Normal ZDD

GenNLC[Y] - [Y] Generalized Error Model ZDD

GenNLC[T] - [T] Generalized Student's t (Asymmetric)

GenNLC[V] - [V] Generalized Student's t (Asymmetric)