Pharmaceutical Calculation Suite
Reports drug content as percent of label claim — with the standard concentration corrected to its assigned potency and the dilution chain counted exactly once.
A general assay reports the drug content of a preparation as a percentage of label claim, by comparing sample response to a reference-standard response. Two details decide whether the number is right: the standard concentration must be corrected to the standard's assigned potency, and the sample's nominal concentration must be built once from weights and dilutions — so no dilution factor is ever applied twice.
Where this is used:
P = assigned potency/purity of the reference standard, on its stated basis (as-is, or anhydrous with a water correction).
Cnom = the sample's nominal concentration, computed once from sample weight, label claim and the TOTAL dilution chain. Because Cnom already contains the full dilution, a separate ×DF multiplier double-counts it — a 1:50 dilution entered both ways reads 50× high.
Why the potency correction matters: USP reference standards carry an assigned value (routinely 98–100%). Using Cstd uncorrected biases every result high by the same factor — material against a 98.0–102.0% window. Calculator modes: single-point (one standard level, replicate injections), multi-point (calibration line across levels, with its own standard purity), and bracketing (standards re-injected through the run against a drift criterion, typically ±1.5–2.0%).
| Symbol | Variable | Units | Description |
|---|---|---|---|
| Asample / Astd | Peak areas | area units | Integrated responses of sample and reference-standard injections under passing system suitability (USP <621>). |
| Cstd,as-prepared | Standard concentration as weighed and diluted | mg/mL | Before potency correction. |
| P | Assigned potency / purity of the standard | % | From the certificate, on its stated basis (as-is vs anhydrous — apply a water correction on the anhydrous basis). USP primary standards are typically ≥ 98%. |
| Cnom | Nominal sample concentration | mg/mL | Built once from sample weight, label claim and the total dilution chain. The dilution appears here and nowhere else. The calculator computes it from the documented prep chain (label claim, units per preparation, stock volume, dilution factor) when left blank; a typed value overrides, and a warning flags a >2% disagreement with the computed chain. |
| %LC | Percent of label claim (result) | % | Reported per replicate and as the mean; the monograph window governs (98.0–102.0% typical). |
| RSD% | Replicate precision (result) | % | Firm criterion, ≤ 2.0% typical for assay. |
Scenario: paracetamol tablets, label 500 mg. Standard: 0.100 mg/mL as prepared, assigned potency 99.8% (as-is), standard area 125,000. Sample prep: one tablet (500 mg API nominal) to 500 mL → 1.000 mg/mL stock; 5.0 mL → 50.0 mL (1:10) → Cnom = 0.100 mg/mL. The 1:10 dilution lives inside Cnom and appears nowhere else. Entered in the calculator as label claim 500 mg, 1 unit per prep, stock volume 500 mL, dilution factor 10 — it computes Cnom = 0.100 mg/mL from that chain.
PharmaCalc returns your %label claim with potency-corrected standards — single-point, multi-point or bracketed. It is computed server-side against the published method and written into a GMP PDF report with the inputs, formula chain, references, document control and signature pages — traceable to the software release that produced it.
Open the General Assay calculator — free demo