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Generalized NLC Models

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 kd 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 kd 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

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

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