How It Works
This calculator works in 3 steps.
Enter the theoretical mass
Type the mass for 100% pure material, or compute it from M, V, and MW.
Enter the assay purity
Type the percent from the certificate of analysis, such as 98.5%.
Read the corrected mass
The calculator divides by the purity fraction and shows the extra mass.
Record the lot
Note the lot number and purity for traceability.
The Formula
The formula divides the theoretical mass by the purity fraction.
m_corrected = m_theoretical × 100 / PΔm = m_corrected − m_theoreticalC_actual = C_target × P / 100- m_theoretical:
- Mass for 100% pure reagent
- P:
- Assay purity (%)
- m_corrected:
- Mass to weigh
A solution needs 10 g of pure KOH. With 85% KOH pellets, weigh 10 × 100 / 85 = 11.76 g.
Conversion Table
The conversion table shows corrected and extra masses for 6 purity levels.
| Theoretical mass | Assay purity | Mass to weigh | Extra mass |
|---|---|---|---|
| 10 g | 99% | 10.1 g | 0.101 g |
| 10 g | 98% | 10.2 g | 0.2041 g |
| 10 g | 95% | 10.53 g | 0.5263 g |
| 10 g | 90% | 11.11 g | 1.111 g |
| 5.844 g | 99.5% | 5.873 g | 0.02937 g |
| 100 g | 85% | 117.6 g | 17.65 g |
What Is the Reagent Purity Correction Calculator?
The Reagent Purity Correction Calculator is a tool that increases the weighed mass of a reagent to account for its stated assay purity, so the solution holds the intended amount of active substance. The corrected mass equals the theoretical mass divided by the purity fraction.
Reagent grades carry assay purities from about 85% to 99.99%. Potassium hydroxide pellets are often 85% KOH, the remainder being water and carbonate. Weighing the uncorrected mass of an 85% reagent gives a solution 15% weaker than planned. The calculator reads the purity from the certificate of analysis and returns the corrected mass.
Common Uses
There are 5 main uses of this calculator.
Technical-grade reagents
Users correct for 85% to 95% purity in bulk chemicals.
Primary standards
Analysts correct for 99.95% assay values on certificates.
Drug substances
Pharmacy and QC staff correct potency for active pharmaceutical ingredients (APIs).
Lot changes
Labs recompute masses when a new lot has a different assay.
Regulated methods
GMP labs document purity corrections in batch records.