HPLC Assay Calculator: % Content and % Label Claim (External Standard)

Turn sample and standard peak areas into % content or % label claim.

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Sample peak area

Standard peak area (mean)

Standard weight mg

Standard volume mL

Standard further dilution ×

Standard purity (as is) %

Sample weight mg

Sample volume mL

Sample further dilution ×

Average unit weight (tablets) mg

Label claim per unit mg

Example: 125 mg of powdered 50 mg tablets (average weight 250 mg). Leave unit weight and label claim blank for a drug substance.

Standard conc.–

Sample conc.–

Content (w/w of sample)–

Label claim–

C_std = W_std·P/(V_std·DF_std) · Content % = (A_s/A_std)·C_std/C_s·100 · mg/unit = (A_s/A_std)·C_std·V_s·DF_s·(W̄/W_s)

How it works

External-standard assay compares the sample response with a reference standard of known purity prepared at a similar concentration. Both concentrations are expressed as the final concentration injected, after every dilution step, so dilution factors must be applied consistently.

Use the standard purity on the same basis as the result: as-is purity for an as-is result, or correct for water or loss on drying separately. For salts, include the free-base correction in the standard purity (purity × MW free base / MW salt) when the label claim is expressed as the free base.