- Other formulas, not included, for calculating Plate numbers include: Half Width, Variance Method, Area / Height & Exponential Modified Gaussian (EMG).
Saturday, June 2, 2018
Number of theoretical plates (N), Calculation Formulas
Number of theoretical plates (N):
Often used to quantify the efficiency (performance) of a column (HPLC or GC). "Plates" are expressed per meter of column length and should be calculated based on a retained peak with ideal peak shape or symmetry.
N = Plates; tr = Retention Time of Peak; w = Peak width; w0.5 = Peak width measured at half height.
Two popular formulas are:
Tangent: USP (United States Pharmacopeia / ASTM)
Best for Gaussian peaks. Peak width is often determined at 13.4% of the peak height (w). Inaccurate for peaks which are non-Gaussian, poorly resolved or tail.
N = 16 (tr / w)2
Half Peak Height: (European Pharmacopeia)
For peaks which are less Gaussian in appearance, using a slightly different formula with the peak width measurement made at the half-height (W0.5). Less accurate for peaks which are poorly resolved or tail.
N = 5.54 (tr / w0.5)2