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HPLC HINTS & TIPS for Chromatographers

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.

 > Bill Letter, 01/01/2013

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