Tip # 119: Common HPLC Calculations
Capacity Factor / Retention Factor:
k1
k1 =
T(R) - T(0) / T(0)
where T(R)
equals the retention time of the peak in minutes and T(0) is the retention time of
an unretained peak.
Tailing Factor: USP, 't'
t =
W(5.0)/tw/2
where tw
equals the distance between peak front and T(R) at 5% of peak height units. W(5.0) equals
width at 5% in minutes.
Theoretical Plates: USP and ASTM, 'N'
N = 5.54 x
(T(R)/W(50))2
Assumes
width at half height (50)
Resolution: USP and ASTM, 'R'
R =
(T(R)(b)-T(R)(a)) x 2.35/(W(50)(b) + W(50)(a))/2
Assumes
width at half height (50) with peaks (a) and (b).
Note: The correct
version of each chromatography formula and/or calculation will often be determined based
on the specific areas pharmaceutical guidelines (Pharmacopoeia). Many different versions
of the above formulas and calculations exist and we are only presenting examples of them.
Please consult the appropriate guideline for your country.
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Bill Letter, 01/01/2013
